2 ''' $RCSfile: perl.man,v $$Revision: 4.0.1.3 $$Date: 91/06/10 01:26:02 $
5 ''' Revision 4.0.1.3 91/06/10 01:26:02 lwall
6 ''' patch10: documented some newer features in addenda
8 ''' Revision 4.0.1.2 91/06/07 11:41:23 lwall
9 ''' patch4: added global modifier for pattern matches
10 ''' patch4: default top-of-form format is now FILEHANDLE_TOP
11 ''' patch4: added $^P variable to control calling of perldb routines
12 ''' patch4: added $^F variable to specify maximum system fd, default 2
13 ''' patch4: changed old $^P to $^X
15 ''' Revision 4.0.1.1 91/04/11 17:50:44 lwall
16 ''' patch1: fixed some typos
18 ''' Revision 4.0 91/03/20 01:38:08 lwall
35 .ie \\n(.$>=3 .ne \\$3
40 ''' Set up \*(-- to give an unbreakable dash;
41 ''' string Tr holds user defined translation string.
42 ''' Bell System Logo is used as a dummy character.
47 .if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
48 .if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
65 perl \- Practical Extraction and Report Language
68 [options] filename args
71 is an interpreted language optimized for scanning arbitrary text files,
72 extracting information from those text files, and printing reports based
74 It's also a good language for many system management tasks.
75 The language is intended to be practical (easy to use, efficient, complete)
76 rather than beautiful (tiny, elegant, minimal).
77 It combines (in the author's opinion, anyway) some of the best features of C,
78 \fIsed\fR, \fIawk\fR, and \fIsh\fR,
79 so people familiar with those languages should have little difficulty with it.
80 (Language historians will also note some vestiges of \fIcsh\fR, Pascal, and
82 Expression syntax corresponds quite closely to C expression syntax.
83 Unlike most Unix utilities,
85 does not arbitrarily limit the size of your data\*(--if you've got
88 can slurp in your whole file as a single string.
89 Recursion is of unlimited depth.
90 And the hash tables used by associative arrays grow as necessary to prevent
93 uses sophisticated pattern matching techniques to scan large amounts of
95 Although optimized for scanning text,
97 can also deal with binary data, and can make dbm files look like associative
98 arrays (where dbm is available).
101 scripts are safer than C programs
102 through a dataflow tracing mechanism which prevents many stupid security holes.
103 If you have a problem that would ordinarily use \fIsed\fR
104 or \fIawk\fR or \fIsh\fR, but it
105 exceeds their capabilities or must run a little faster,
106 and you don't want to write the silly thing in C, then
109 There are also translators to turn your
120 looks for your script in one of the following places:
122 Specified line by line via
124 switches on the command line.
126 Contained in the file specified by the first filename on the command line.
127 (Note that systems supporting the #! notation invoke interpreters this way.)
129 Passed in implicitly via standard input.
130 This only works if there are no filename arguments\*(--to pass
133 script you must explicitly specify a \- for the script name.
135 After locating your script,
137 compiles it to an internal form.
138 If the script is syntactically correct, it is executed.
140 Note: on first reading this section may not make much sense to you. It's here
141 at the front for easy reference.
143 A single-character option may be combined with the following option, if any.
144 This is particularly useful when invoking a script using the #! construct which
145 only allows one argument. Example:
149 #!/usr/bin/perl \-spi.bak # same as \-s \-p \-i.bak
156 specifies the record separator ($/) as an octal number.
157 If there are no digits, the null character is the separator.
158 Other switches may precede or follow the digits.
159 For example, if you have a version of
161 which can print filenames terminated by the null character, you can say this:
164 find . \-name '*.bak' \-print0 | perl \-n0e unlink
167 The special value 00 will cause Perl to slurp files in paragraph mode.
168 The value 0777 will cause Perl to slurp files whole since there is no
169 legal character with that value.
172 turns on autosplit mode when used with a
176 An implicit split command to the @F array
177 is done as the first thing inside the implicit while loop produced by
184 perl \-ane \'print pop(@F), "\en";\'
190 print pop(@F), "\en";
198 to check the syntax of the script and then exit without executing it.
201 runs the script under the perl debugger.
202 See the section on Debugging.
205 sets debugging flags.
206 To watch how it executes your script, use
208 (This only works if debugging is compiled into your
210 Another nice value is \-D1024, which lists your compiled syntax tree.
211 And \-D512 displays compiled regular expressions.
213 .BI \-e " commandline"
214 may be used to enter one line of script.
217 commands may be given to build up a multi-line script.
222 will not look for a script filename in the argument list.
225 specifies that files processed by the <> construct are to be edited
227 It does this by renaming the input file, opening the output file by the
228 same name, and selecting that output file as the default for print statements.
229 The extension, if supplied, is added to the name of the
230 old file to make a backup copy.
231 If no extension is supplied, no backup is made.
232 Saying \*(L"perl \-p \-i.bak \-e "s/foo/bar/;" .\|.\|. \*(R" is the same as using
237 #!/usr/bin/perl \-pi.bak
240 which is equivalent to
245 if ($ARGV ne $oldargv) {
246 rename($ARGV, $ARGV . \'.bak\');
247 open(ARGVOUT, ">$ARGV");
254 print; # this prints to original filename
261 form doesn't need to compare $ARGV to $oldargv to know when
262 the filename has changed.
263 It does, however, use ARGVOUT for the selected filehandle.
266 is restored as the default output filehandle after the loop.
268 You can use eof to locate the end of each input file, in case you want
269 to append to each file, or reset line numbering (see example under eof).
272 may be used in conjunction with
274 to tell the C preprocessor where to look for include files.
275 By default /usr/include and /usr/lib/perl are searched.
278 enables automatic line-ending processing. It has two effects:
279 first, it automatically chops the line terminator when used with
283 and second, it assigns $\e to have the value of
285 so that any print statements will have that line terminator added back on. If
287 is omitted, sets $\e to the current value of $/.
288 For instance, to trim lines to 80 columns:
291 perl -lpe \'substr($_, 80) = ""\'
294 Note that the assignment $\e = $/ is done when the switch is processed,
295 so the input record separator can be different than the output record
298 switch is followed by a
303 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
306 This sets $\e to newline and then sets $/ to the null character.
311 to assume the following loop around your script, which makes it iterate
312 over filename arguments somewhat like \*(L"sed \-n\*(R" or \fIawk\fR:
317 .\|.\|. # your script goes here
321 Note that the lines are not printed by default.
324 to have lines printed.
325 Here is an efficient way to delete all files older than a week:
328 find . \-mtime +7 \-print | perl \-nle \'unlink;\'
331 This is faster than using the \-exec switch of find because you don't have to
332 start a process on every filename found.
337 to assume the following loop around your script, which makes it iterate
338 over filename arguments somewhat like \fIsed\fR:
343 .\|.\|. # your script goes here
349 Note that the lines are printed automatically.
350 To suppress printing use the
360 causes your script to be run through the C preprocessor before
363 (Since both comments and cpp directives begin with the # character,
364 you should avoid starting comments with any words recognized
365 by the C preprocessor such as \*(L"if\*(R", \*(L"else\*(R" or \*(L"define\*(R".)
368 enables some rudimentary switch parsing for switches on the command line
369 after the script name but before any filename arguments (or before a \-\|\-).
370 Any switch found there is removed from @ARGV and sets the corresponding variable in the
373 The following script prints \*(L"true\*(R" if and only if the script is
374 invoked with a \-xyz switch.
379 if ($xyz) { print "true\en"; }
386 use the PATH environment variable to search for the script
387 (unless the name of the script starts with a slash).
388 Typically this is used to emulate #! startup on machines that don't
389 support #!, in the following manner:
393 eval "exec /usr/bin/perl \-S $0 $*"
394 if $running_under_some_shell;
397 The system ignores the first line and feeds the script to /bin/sh,
398 which proceeds to try to execute the
400 script as a shell script.
401 The shell executes the second line as a normal shell command, and thus
405 On some systems $0 doesn't always contain the full pathname,
410 to search for the script if necessary.
413 locates the script, it parses the lines and ignores them because
414 the variable $running_under_some_shell is never true.
415 A better construct than $* would be ${1+"$@"}, which handles embedded spaces
416 and such in the filenames, but doesn't work if the script is being interpreted
418 In order to start up sh rather than csh, some systems may have to replace the
419 #! line with a line containing just
420 a colon, which will be politely ignored by perl.
421 Other systems can't control that, and need a totally devious construct that
422 will work under any of csh, sh or perl, such as the following:
426 eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
427 & eval 'exec /usr/bin/perl -S $0 $argv:q'
435 to dump core after compiling your script.
436 You can then take this core dump and turn it into an executable file
437 by using the undump program (not supplied).
438 This speeds startup at the expense of some disk space (which you can
439 minimize by stripping the executable).
440 (Still, a "hello world" executable comes out to about 200K on my machine.)
441 If you are going to run your executable as a set-id program then you
442 should probably compile it using taintperl rather than normal perl.
443 If you want to execute a portion of your script before dumping, use the
444 dump operator instead.
445 Note: availability of undump is platform specific and may not be available
446 for a specific port of perl.
451 to do unsafe operations.
452 Currently the only \*(L"unsafe\*(R" operation is the unlinking of directories while
453 running as superuser.
456 prints the version and patchlevel of your
461 prints warnings about identifiers that are mentioned only once, and scalar
462 variables that are used before being set.
463 Also warns about redefined subroutines, and references to undefined
464 filehandles or filehandles opened readonly that you are attempting to
466 Also warns you if you use == on values that don't look like numbers, and if
467 your subroutines recurse more than 100 deep.
472 that the script is embedded in a message.
473 Leading garbage will be discarded until the first line that starts
474 with #! and contains the string "perl".
475 Any meaningful switches on that line will be applied (but only one
476 group of switches, as with normal #! processing).
477 If a directory name is specified, Perl will switch to that directory
478 before running the script.
481 switch only controls the the disposal of leading garbage.
482 The script must be terminated with __END__ if there is trailing garbage
483 to be ignored (the script can process any or all of the trailing garbage
484 via the DATA filehandle if desired).
485 .Sh "Data Types and Objects"
488 has three data types: scalars, arrays of scalars, and
489 associative arrays of scalars.
490 Normal arrays are indexed by number, and associative arrays by string.
492 The interpretation of operations and values in perl sometimes
493 depends on the requirements
494 of the context around the operation or value.
495 There are three major contexts: string, numeric and array.
496 Certain operations return array values
497 in contexts wanting an array, and scalar values otherwise.
498 (If this is true of an operation it will be mentioned in the documentation
500 Operations which return scalars don't care whether the context is looking
501 for a string or a number, but
502 scalar variables and values are interpreted as strings or numbers
503 as appropriate to the context.
504 A scalar is interpreted as TRUE in the boolean sense if it is not the null
506 Booleans returned by operators are 1 for true and 0 or \'\' (the null
509 There are actually two varieties of null string: defined and undefined.
510 Undefined null strings are returned when there is no real value for something,
511 such as when there was an error, or at end of file, or when you refer
512 to an uninitialized variable or element of an array.
513 An undefined null string may become defined the first time you access it, but
514 prior to that you can use the defined() operator to determine whether the
515 value is defined or not.
517 References to scalar variables always begin with \*(L'$\*(R', even when referring
518 to a scalar that is part of an array.
523 $days \h'|2i'# a simple scalar variable
524 $days[28] \h'|2i'# 29th element of array @days
525 $days{\'Feb\'}\h'|2i'# one value from an associative array
526 $#days \h'|2i'# last index of array @days
528 but entire arrays or array slices are denoted by \*(L'@\*(R':
530 @days \h'|2i'# ($days[0], $days[1],\|.\|.\|. $days[n])
531 @days[3,4,5]\h'|2i'# same as @days[3.\|.5]
532 @days{'a','c'}\h'|2i'# same as ($days{'a'},$days{'c'})
534 and entire associative arrays are denoted by \*(L'%\*(R':
536 %days \h'|2i'# (key1, val1, key2, val2 .\|.\|.)
539 Any of these eight constructs may serve as an lvalue,
540 that is, may be assigned to.
541 (It also turns out that an assignment is itself an lvalue in
542 certain contexts\*(--see examples under s, tr and chop.)
543 Assignment to a scalar evaluates the righthand side in a scalar context,
544 while assignment to an array or array slice evaluates the righthand side
547 You may find the length of array @days by evaluating
548 \*(L"$#days\*(R", as in
550 (Actually, it's not the length of the array, it's the subscript of the last element, since there is (ordinarily) a 0th element.)
551 Assigning to $#days changes the length of the array.
552 Shortening an array by this method does not actually destroy any values.
553 Lengthening an array that was previously shortened recovers the values that
554 were in those elements.
555 You can also gain some measure of efficiency by preextending an array that
557 (You can also extend an array by assigning to an element that is off the
559 This differs from assigning to $#whatever in that intervening values
560 are set to null rather than recovered.)
561 You can truncate an array down to nothing by assigning the null list () to
563 The following are exactly equivalent
567 $#whatever = $[ \- 1;
571 If you evaluate an array in a scalar context, it returns the length of
573 The following is always true:
576 @whatever == $#whatever \- $[ + 1;
580 Multi-dimensional arrays are not directly supported, but see the discussion
581 of the $; variable later for a means of emulating multiple subscripts with
582 an associative array.
583 You could also write a subroutine to turn multiple subscripts into a single
586 Every data type has its own namespace.
587 You can, without fear of conflict, use the same name for a scalar variable,
588 an array, an associative array, a filehandle, a subroutine name, and/or
590 Since variable and array references always start with \*(L'$\*(R', \*(L'@\*(R',
591 or \*(L'%\*(R', the \*(L"reserved\*(R" words aren't in fact reserved
592 with respect to variable names.
593 (They ARE reserved with respect to labels and filehandles, however, which
594 don't have an initial special character.
595 Hint: you could say open(LOG,\'logfile\') rather than open(log,\'logfile\').
596 Using uppercase filehandles also improves readability and protects you
597 from conflict with future reserved words.)
598 Case IS significant\*(--\*(L"FOO\*(R", \*(L"Foo\*(R" and \*(L"foo\*(R" are all
600 Names which start with a letter may also contain digits and underscores.
601 Names which do not start with a letter are limited to one character,
602 e.g. \*(L"$%\*(R" or \*(L"$$\*(R".
603 (Most of the one character names have a predefined significance to
607 Numeric literals are specified in any of the usual floating point or
619 String literals are delimited by either single or double quotes.
620 They work much like shell quotes:
621 double-quoted string literals are subject to backslash and variable
622 substitution; single-quoted strings are not (except for \e\' and \e\e).
623 The usual backslash rules apply for making characters such as newline, tab,
624 etc., as well as some more exotic forms:
637 \el lowercase next char
638 \eu uppercase next char
639 \eL lowercase till \eE
640 \eU uppercase till \eE
641 \eE end case modification
644 You can also embed newlines directly in your strings, i.e. they can end on
645 a different line than they begin.
646 This is nice, but if you forget your trailing quote, the error will not be
649 finds another line containing the quote character, which
650 may be much further on in the script.
651 Variable substitution inside strings is limited to scalar variables, normal
652 array values, and array slices.
653 (In other words, identifiers beginning with $ or @, followed by an optional
654 bracketed expression as a subscript.)
655 The following code segment prints out \*(L"The price is $100.\*(R"
659 $Price = \'$100\';\h'|3.5i'# not interpreted
660 print "The price is $Price.\e\|n";\h'|3.5i'# interpreted
663 Note that you can put curly brackets around the identifier to delimit it
664 from following alphanumerics.
665 Also note that a single quoted string must be separated from a preceding
666 word by a space, since single quote is a valid character in an identifier
669 Two special literals are __LINE__ and __FILE__, which represent the current
670 line number and filename at that point in your program.
671 They may only be used as separate tokens; they will not be interpolated
673 In addition, the token __END__ may be used to indicate the logical end of the
674 script before the actual end of file.
675 Any following text is ignored (but may be read via the DATA filehandle).
676 The two control characters ^D and ^Z are synonyms for __END__.
678 A word that doesn't have any other interpretation in the grammar will be
679 treated as if it had single quotes around it.
680 For this purpose, a word consists only of alphanumeric characters and underline,
681 and must start with an alphabetic character.
682 As with filehandles and labels, a bare word that consists entirely of
683 lowercase letters risks conflict with future reserved words, and if you
686 switch, Perl will warn you about any such words.
688 Array values are interpolated into double-quoted strings by joining all the
689 elements of the array with the delimiter specified in the $" variable,
691 (Since in versions of perl prior to 3.0 the @ character was not a metacharacter
692 in double-quoted strings, the interpolation of @array, $array[EXPR],
693 @array[LIST], $array{EXPR}, or @array{LIST} only happens if array is
694 referenced elsewhere in the program or is predefined.)
695 The following are equivalent:
699 $temp = join($",@ARGV);
705 Within search patterns (which also undergo double-quotish substitution)
706 there is a bad ambiguity: Is /$foo[bar]/ to be
707 interpreted as /${foo}[bar]/ (where [bar] is a character class for the
708 regular expression) or as /${foo[bar]}/ (where [bar] is the subscript to
710 If @foo doesn't otherwise exist, then it's obviously a character class.
711 If @foo exists, perl takes a good guess about [bar], and is almost always right.
712 If it does guess wrong, or if you're just plain paranoid,
713 you can force the correct interpretation with curly brackets as above.
715 A line-oriented form of quoting is based on the shell here-is syntax.
716 Following a << you specify a string to terminate the quoted material, and all lines
717 following the current line down to the terminating string are the value
719 The terminating string may be either an identifier (a word), or some
721 If quoted, the type of quotes you use determines the treatment of the text,
722 just as in regular quoting.
723 An unquoted identifier works like double quotes.
724 There must be no space between the << and the identifier.
725 (If you put a space it will be treated as a null identifier, which is
726 valid, and matches the first blank line\*(--see Merry Christmas example below.)
727 The terminating string must appear by itself (unquoted and with no surrounding
728 whitespace) on the terminating line.
731 print <<EOF; # same as above
735 print <<"EOF"; # same as above
739 print << x 10; # null identifier is delimiter
742 print <<`EOC`; # execute commands
747 print <<foo, <<bar; # you can stack them
754 Array literals are denoted by separating individual values by commas, and
755 enclosing the list in parentheses:
761 In a context not requiring an array value, the value of the array literal
762 is the value of the final element, as in the C comma operator.
767 @foo = (\'cc\', \'\-E\', $bar);
769 assigns the entire array value to array foo, but
771 $foo = (\'cc\', \'\-E\', $bar);
774 assigns the value of variable bar to variable foo.
775 Note that the value of an actual array in a scalar context is the length
776 of the array; the following assigns to $foo the value 3:
780 @foo = (\'cc\', \'\-E\', $bar);
781 $foo = @foo; # $foo gets 3
784 You may have an optional comma before the closing parenthesis of an
785 array literal, so that you can say:
795 When a LIST is evaluated, each element of the list is evaluated in
796 an array context, and the resulting array value is interpolated into LIST
797 just as if each individual element were a member of LIST. Thus arrays
798 lose their identity in a LIST\*(--the list
802 contains all the elements of @foo followed by all the elements of @bar,
803 followed by all the elements returned by the subroutine named SomeSub.
805 A list value may also be subscripted like a normal array.
809 $time = (stat($file))[8]; # stat returns array value
810 $digit = ('a','b','c','d','e','f')[$digit-10];
811 return (pop(@foo),pop(@foo))[0];
815 Array lists may be assigned to if and only if each element of the list
819 ($a, $b, $c) = (1, 2, 3);
821 ($map{\'red\'}, $map{\'blue\'}, $map{\'green\'}) = (0x00f, 0x0f0, 0xf00);
823 The final element may be an array or an associative array:
825 ($a, $b, @rest) = split;
826 local($a, $b, %rest) = @_;
829 You can actually put an array anywhere in the list, but the first array
830 in the list will soak up all the values, and anything after it will get
832 This may be useful in a local().
834 An associative array literal contains pairs of values to be interpreted
835 as a key and a value:
839 # same as map assignment above
840 %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
843 Array assignment in a scalar context returns the number of elements
844 produced by the expression on the right side of the assignment:
847 $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
851 There are several other pseudo-literals that you should know about.
852 If a string is enclosed by backticks (grave accents), it first undergoes
853 variable substitution just like a double quoted string.
854 It is then interpreted as a command, and the output of that command
855 is the value of the pseudo-literal, like in a shell.
856 In a scalar context, a single string consisting of all the output is
858 In an array context, an array of values is returned, one for each line
860 (You can set $/ to use a different line terminator.)
861 The command is executed each time the pseudo-literal is evaluated.
862 The status value of the command is returned in $? (see Predefined Names
863 for the interpretation of $?).
864 Unlike in \f2csh\f1, no translation is done on the return
865 data\*(--newlines remain newlines.
866 Unlike in any of the shells, single quotes do not hide variable names
867 in the command from interpretation.
868 To pass a $ through to the shell you need to hide it with a backslash.
870 Evaluating a filehandle in angle brackets yields the next line
871 from that file (newline included, so it's never false until EOF, at
872 which time an undefined value is returned).
873 Ordinarily you must assign that value to a variable,
874 but there is one situation where an automatic assignment happens.
875 If (and only if) the input symbol is the only thing inside the conditional of a
878 automatically assigned to the variable \*(L"$_\*(R".
879 (This may seem like an odd thing to you, but you'll use the construct
883 Anyway, the following lines are equivalent to each other:
887 while ($_ = <STDIN>) { print; }
888 while (<STDIN>) { print; }
889 for (\|;\|<STDIN>;\|) { print; }
890 print while $_ = <STDIN>;
905 will also work except in packages, where they would be interpreted as
906 local identifiers rather than global.)
907 Additional filehandles may be created with the
911 If a <FILEHANDLE> is used in a context that is looking for an array, an array
912 consisting of all the input lines is returned, one line per array element.
913 It's easy to make a LARGE data space this way, so use with care.
915 The null filehandle <> is special and can be used to emulate the behavior of
916 \fIsed\fR and \fIawk\fR.
917 Input from <> comes either from standard input, or from each file listed on
919 Here's how it works: the first time <> is evaluated, the ARGV array is checked,
920 and if it is null, $ARGV[0] is set to \'-\', which when opened gives you standard
922 The ARGV array is then processed as a list of filenames.
928 .\|.\|. # code for each line
934 unshift(@ARGV, \'\-\') \|if \|$#ARGV < $[;
935 while ($ARGV = shift) {
938 .\|.\|. # code for each line
943 except that it isn't as cumbersome to say.
944 It really does shift array ARGV and put the current filename into
946 It also uses filehandle ARGV internally.
947 You can modify @ARGV before the first <> as long as you leave the first
948 filename at the beginning of the array.
949 Line numbers ($.) continue as if the input was one big happy file.
950 (But see example under eof for how to reset line numbers on each file.)
953 If you want to set @ARGV to your own list of files, go right ahead.
954 If you want to pass switches into your script, you can
955 put a loop on the front like this:
959 while ($_ = $ARGV[0], /\|^\-/\|) {
961 last if /\|^\-\|\-$\|/\|;
962 /\|^\-D\|(.*\|)/ \|&& \|($debug = $1);
963 /\|^\-v\|/ \|&& \|$verbose++;
964 .\|.\|. # other switches
967 .\|.\|. # code for each line
971 The <> symbol will return FALSE only once.
972 If you call it again after this it will assume you are processing another
973 @ARGV list, and if you haven't set @ARGV, will input from
976 If the string inside the angle brackets is a reference to a scalar variable
978 then that variable contains the name of the filehandle to input from.
980 If the string inside angle brackets is not a filehandle, it is interpreted
981 as a filename pattern to be globbed, and either an array of filenames or the
982 next filename in the list is returned, depending on context.
983 One level of $ interpretation is done first, but you can't say <$foo>
984 because that's an indirect filehandle as explained in the previous
986 You could insert curly brackets to force interpretation as a
987 filename glob: <${foo}>.
999 open(foo, "echo *.c | tr \-s \' \et\er\ef\' \'\e\e012\e\e012\e\e012\e\e012\'|");
1006 In fact, it's currently implemented that way.
1007 (Which means it will not work on filenames with spaces in them unless
1008 you have /bin/csh on your machine.)
1009 Of course, the shortest way to do the above is:
1019 script consists of a sequence of declarations and commands.
1020 The only things that need to be declared in
1022 are report formats and subroutines.
1023 See the sections below for more information on those declarations.
1024 All uninitialized user-created objects are assumed to
1025 start with a null or 0 value until they
1026 are defined by some explicit operation such as assignment.
1027 The sequence of commands is executed just once, unlike in
1031 scripts, where the sequence of commands is executed for each input line.
1032 While this means that you must explicitly loop over the lines of your input file
1033 (or files), it also means you have much more control over which files and which
1035 (Actually, I'm lying\*(--it is possible to do an implicit loop with either the
1041 A declaration can be put anywhere a command can, but has no effect on the
1042 execution of the primary sequence of commands\*(--declarations all take effect
1044 Typically all the declarations are put at the beginning or the end of the script.
1047 is, for the most part, a free-form language.
1048 (The only exception to this is format declarations, for fairly obvious reasons.)
1049 Comments are indicated by the # character, and extend to the end of the line.
1050 If you attempt to use /* */ C comments, it will be interpreted either as
1051 division or pattern matching, depending on the context.
1053 .Sh "Compound statements"
1056 a sequence of commands may be treated as one command by enclosing it
1058 We will call this a BLOCK.
1060 The following compound commands may be used to control flow:
1065 if (EXPR) BLOCK else BLOCK
1066 if (EXPR) BLOCK elsif (EXPR) BLOCK .\|.\|. else BLOCK
1067 LABEL while (EXPR) BLOCK
1068 LABEL while (EXPR) BLOCK continue BLOCK
1069 LABEL for (EXPR; EXPR; EXPR) BLOCK
1070 LABEL foreach VAR (ARRAY) BLOCK
1071 LABEL BLOCK continue BLOCK
1074 Note that, unlike C and Pascal, these are defined in terms of BLOCKs, not
1076 This means that the curly brackets are \fIrequired\fR\*(--no dangling statements allowed.
1077 If you want to write conditionals without curly brackets there are several
1078 other ways to do it.
1079 The following all do the same thing:
1083 if (!open(foo)) { die "Can't open $foo: $!"; }
1084 die "Can't open $foo: $!" unless open(foo);
1085 open(foo) || die "Can't open $foo: $!"; # foo or bust!
1086 open(foo) ? \'hi mom\' : die "Can't open $foo: $!";
1087 # a bit exotic, that last one
1093 statement is straightforward.
1094 Since BLOCKs are always bounded by curly brackets, there is never any
1095 ambiguity about which
1104 the sense of the test is reversed.
1108 statement executes the block as long as the expression is true
1109 (does not evaluate to the null string or 0).
1110 The LABEL is optional, and if present, consists of an identifier followed by
1112 The LABEL identifies the loop for the loop control statements
1120 BLOCK, it is always executed just before
1121 the conditional is about to be evaluated again, similarly to the third part
1125 Thus it can be used to increment a loop variable, even when the loop has
1126 been continued via the
1128 statement (similar to the C \*(L"continue\*(R" statement).
1132 is replaced by the word
1134 the sense of the test is reversed, but the conditional is still tested before
1135 the first iteration.
1141 statement, you may replace \*(L"(EXPR)\*(R" with a BLOCK, and the conditional
1142 is true if the value of the last command in that block is true.
1146 loop works exactly like the corresponding
1152 for ($i = 1; $i < 10; $i++) {
1166 The foreach loop iterates over a normal array value and sets the variable
1167 VAR to be each element of the array in turn.
1168 The variable is implicitly local to the loop, and regains its former value
1169 upon exiting the loop.
1170 The \*(L"foreach\*(R" keyword is actually identical to the \*(L"for\*(R" keyword,
1171 so you can use \*(L"foreach\*(R" for readability or \*(L"for\*(R" for brevity.
1172 If VAR is omitted, $_ is set to each value.
1173 If ARRAY is an actual array (as opposed to an expression returning an array
1174 value), you can modify each element of the array
1175 by modifying VAR inside the loop.
1180 for (@ary) { s/foo/bar/; }
1182 foreach $elem (@elements) {
1187 for ((10,9,8,7,6,5,4,3,2,1,\'BOOM\')) {
1188 print $_, "\en"; sleep(1);
1191 for (1..15) { print "Merry Christmas\en"; }
1194 foreach $item (split(/:[\e\e\en:]*/, $ENV{\'TERMCAP\'})) {
1195 print "Item: $item\en";
1200 The BLOCK by itself (labeled or not) is equivalent to a loop that executes
1202 Thus you can use any of the loop control statements in it to leave or
1207 This construct is particularly nice for doing case structures.
1212 if (/^abc/) { $abc = 1; last foo; }
1213 if (/^def/) { $def = 1; last foo; }
1214 if (/^xyz/) { $xyz = 1; last foo; }
1219 There is no official switch statement in perl, because there
1220 are already several ways to write the equivalent.
1221 In addition to the above, you could write
1226 $abc = 1, last foo if /^abc/;
1227 $def = 1, last foo if /^def/;
1228 $xyz = 1, last foo if /^xyz/;
1236 /^abc/ && do { $abc = 1; last foo; };
1237 /^def/ && do { $def = 1; last foo; };
1238 /^xyz/ && do { $xyz = 1; last foo; };
1246 /^abc/ && ($abc = 1, last foo);
1247 /^def/ && ($def = 1, last foo);
1248 /^xyz/ && ($xyz = 1, last foo);
1265 As it happens, these are all optimized internally to a switch structure,
1266 so perl jumps directly to the desired statement, and you needn't worry
1267 about perl executing a lot of unnecessary statements when you have a string
1268 of 50 elsifs, as long as you are testing the same simple scalar variable
1269 using ==, eq, or pattern matching as above.
1270 (If you're curious as to whether the optimizer has done this for a particular
1271 case statement, you can use the \-D1024 switch to list the syntax tree
1273 .Sh "Simple statements"
1274 The only kind of simple statement is an expression evaluated for its side
1276 Every expression (simple statement) must be terminated with a semicolon.
1277 Note that this is like C, but unlike Pascal (and
1280 Any simple statement may optionally be followed by a
1281 single modifier, just before the terminating semicolon.
1282 The possible modifiers are:
1296 modifiers have the expected semantics.
1301 modifiers also have the expected semantics (conditional evaluated first),
1302 except when applied to a do-BLOCK or a do-SUBROUTINE command,
1303 in which case the block executes once before the conditional is evaluated.
1304 This is so that you can write loops like:
1311 } until $_ \|eq \|".\|\e\|n";
1316 operator below. Note also that the loop control commands described later will
1317 NOT work in this construct, since modifiers don't take loop labels.
1322 expressions work almost exactly like C expressions, only the differences
1323 will be mentioned here.
1329 The exponentiation operator.
1331 The exponentiation assignment operator.
1333 The null list, used to initialize an array to null.
1335 Concatenation of two strings.
1337 The concatenation assignment operator.
1339 String equality (== is numeric equality).
1340 For a mnemonic just think of \*(L"eq\*(R" as a string.
1341 (If you are used to the
1343 behavior of using == for either string or numeric equality
1344 based on the current form of the comparands, beware!
1345 You must be explicit here.)
1347 String inequality (!= is numeric inequality).
1351 String greater than.
1353 String less than or equal.
1355 String greater than or equal.
1357 String comparison, returning -1, 0, or 1.
1359 Numeric comparison, returning -1, 0, or 1.
1361 Certain operations search or modify the string \*(L"$_\*(R" by default.
1362 This operator makes that kind of operation work on some other string.
1363 The right argument is a search pattern, substitution, or translation.
1364 The left argument is what is supposed to be searched, substituted, or
1365 translated instead of the default \*(L"$_\*(R".
1366 The return value indicates the success of the operation.
1367 (If the right argument is an expression other than a search pattern,
1368 substitution, or translation, it is interpreted as a search pattern
1370 This is less efficient than an explicit search, since the pattern must
1371 be compiled every time the expression is evaluated.)
1372 The precedence of this operator is lower than unary minus and autoincrement/decrement, but higher than everything else.
1374 Just like =~ except the return value is negated.
1376 The repetition operator.
1377 Returns a string consisting of the left operand repeated the
1378 number of times specified by the right operand.
1379 In an array context, if the left operand is a list in parens, it repeats
1383 print \'\-\' x 80; # print row of dashes
1384 print \'\-\' x80; # illegal, x80 is identifier
1386 print "\et" x ($tab/8), \' \' x ($tab%8); # tab over
1388 @ones = (1) x 80; # an array of 80 1's
1389 @ones = (5) x @ones; # set all elements to 5
1393 The repetition assignment operator.
1394 Only works on scalars.
1396 The range operator, which is really two different operators depending
1398 In an array context, returns an array of values counting (by ones)
1399 from the left value to the right value.
1400 This is useful for writing \*(L"for (1..10)\*(R" loops and for doing
1401 slice operations on arrays.
1403 In a scalar context, .\|. returns a boolean value.
1404 The operator is bistable, like a flip-flop..
1405 Each .\|. operator maintains its own boolean state.
1406 It is false as long as its left operand is false.
1407 Once the left operand is true, the range operator stays true
1408 until the right operand is true,
1409 AFTER which the range operator becomes false again.
1410 (It doesn't become false till the next time the range operator is evaluated.
1411 It can become false on the same evaluation it became true, but it still returns
1413 The right operand is not evaluated while the operator is in the \*(L"false\*(R" state,
1414 and the left operand is not evaluated while the operator is in the \*(L"true\*(R" state.
1415 The scalar .\|. operator is primarily intended for doing line number ranges
1417 the fashion of \fIsed\fR or \fIawk\fR.
1418 The precedence is a little lower than || and &&.
1419 The value returned is either the null string for false, or a sequence number
1420 (beginning with 1) for true.
1421 The sequence number is reset for each range encountered.
1422 The final sequence number in a range has the string \'E0\' appended to it, which
1423 doesn't affect its numeric value, but gives you something to search for if you
1424 want to exclude the endpoint.
1425 You can exclude the beginning point by waiting for the sequence number to be
1427 If either operand of scalar .\|. is static, that operand is implicitly compared
1428 to the $. variable, the current line number.
1433 As a scalar operator:
1434 if (101 .\|. 200) { print; } # print 2nd hundred lines
1436 next line if (1 .\|. /^$/); # skip header lines
1438 s/^/> / if (/^$/ .\|. eof()); # quote body
1441 As an array operator:
1442 for (101 .\|. 200) { print; } # print $_ 100 times
1444 @foo = @foo[$[ .\|. $#foo]; # an expensive no-op
1445 @foo = @foo[$#foo-4 .\|. $#foo]; # slice last 5 items
1450 This unary operator takes one argument, either a filename or a filehandle,
1451 and tests the associated file to see if something is true about it.
1452 If the argument is omitted, tests $_, except for \-t, which tests
1454 It returns 1 for true and \'\' for false, or the undefined value if the
1456 Precedence is higher than logical and relational operators, but lower than
1457 arithmetic operators.
1458 The operator may be any of:
1460 \-r File is readable by effective uid.
1461 \-w File is writable by effective uid.
1462 \-x File is executable by effective uid.
1463 \-o File is owned by effective uid.
1464 \-R File is readable by real uid.
1465 \-W File is writable by real uid.
1466 \-X File is executable by real uid.
1467 \-O File is owned by real uid.
1469 \-z File has zero size.
1470 \-s File has non-zero size (returns size).
1471 \-f File is a plain file.
1472 \-d File is a directory.
1473 \-l File is a symbolic link.
1474 \-p File is a named pipe (FIFO).
1475 \-S File is a socket.
1476 \-b File is a block special file.
1477 \-c File is a character special file.
1478 \-u File has setuid bit set.
1479 \-g File has setgid bit set.
1480 \-k File has sticky bit set.
1481 \-t Filehandle is opened to a tty.
1482 \-T File is a text file.
1483 \-B File is a binary file (opposite of \-T).
1484 \-M Age of file in days when script started.
1485 \-A Same for access time.
1486 \-C Same for inode change time.
1489 The interpretation of the file permission operators \-r, \-R, \-w, \-W, \-x and \-X
1490 is based solely on the mode of the file and the uids and gids of the user.
1491 There may be other reasons you can't actually read, write or execute the file.
1492 Also note that, for the superuser, \-r, \-R, \-w and \-W always return 1, and
1493 \-x and \-X return 1 if any execute bit is set in the mode.
1494 Scripts run by the superuser may thus need to do a stat() in order to determine
1495 the actual mode of the file, or temporarily set the uid to something else.
1503 next unless \-f $_; # ignore specials
1508 Note that \-s/a/b/ does not do a negated substitution.
1509 Saying \-exp($foo) still works as expected, however\*(--only single letters
1510 following a minus are interpreted as file tests.
1512 The \-T and \-B switches work as follows.
1513 The first block or so of the file is examined for odd characters such as
1514 strange control codes or metacharacters.
1515 If too many odd characters (>10%) are found, it's a \-B file, otherwise it's a \-T file.
1516 Also, any file containing null in the first block is considered a binary file.
1517 If \-T or \-B is used on a filehandle, the current stdio buffer is examined
1518 rather than the first block.
1519 Both \-T and \-B return TRUE on a null file, or a file at EOF when testing
1522 If any of the file tests (or either stat operator) are given the special
1523 filehandle consisting of a solitary underline, then the stat structure
1524 of the previous file test (or stat operator) is used, saving a system
1526 (This doesn't work with \-t, and you need to remember that lstat and -l
1527 will leave values in the stat structure for the symbolic link, not the
1532 print "Can do.\en" if -r $a || -w _ || -x _;
1536 print "Readable\en" if -r _;
1537 print "Writable\en" if -w _;
1538 print "Executable\en" if -x _;
1539 print "Setuid\en" if -u _;
1540 print "Setgid\en" if -g _;
1541 print "Sticky\en" if -k _;
1542 print "Text\en" if -T _;
1543 print "Binary\en" if -B _;
1547 Here is what C has that
1551 Address-of operator.
1553 Dereference-address operator.
1555 Type casting operator.
1559 does a certain amount of expression evaluation at compile time, whenever
1560 it determines that all of the arguments to an operator are static and have
1562 In particular, string concatenation happens at compile time between literals that don't do variable substitution.
1563 Backslash interpretation also happens at compile time.
1568 \'Now is the time for all\' . "\|\e\|n" .
1569 \'good men to come to.\'
1572 and this all reduces to one string internally.
1574 The autoincrement operator has a little extra built-in magic to it.
1575 If you increment a variable that is numeric, or that has ever been used in
1576 a numeric context, you get a normal increment.
1577 If, however, the variable has only been used in string contexts since it
1578 was set, and has a value that is not null and matches the
1579 pattern /^[a\-zA\-Z]*[0\-9]*$/, the increment is done
1580 as a string, preserving each character within its range, with carry:
1583 print ++($foo = \'99\'); # prints \*(L'100\*(R'
1584 print ++($foo = \'a0\'); # prints \*(L'a1\*(R'
1585 print ++($foo = \'Az\'); # prints \*(L'Ba\*(R'
1586 print ++($foo = \'zz\'); # prints \*(L'aaa\*(R'
1589 The autodecrement is not magical.
1591 The range operator (in an array context) makes use of the magical
1592 autoincrement algorithm if the minimum and maximum are strings.
1595 @alphabet = (\'A\' .. \'Z\');
1597 to get all the letters of the alphabet, or
1599 $hexdigit = (0 .. 9, \'a\' .. \'f\')[$num & 15];
1601 to get a hexadecimal digit, or
1603 @z2 = (\'01\' .. \'31\'); print @z2[$mday];
1605 to get dates with leading zeros.
1606 (If the final value specified is not in the sequence that the magical increment
1607 would produce, the sequence goes until the next value would be longer than
1608 the final value specified.)
1610 The || and && operators differ from C's in that, rather than returning 0 or 1,
1611 they return the last value evaluated.
1612 Thus, a portable way to find out the home directory might be:
1615 $home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
1616 (getpwuid($<))[7] || die "You're homeless!\en";
1620 Along with the literals and variables mentioned earlier,
1621 the operations in the following section can serve as terms in an expression.
1622 Some of these operations take a LIST as an argument.
1623 Such a list can consist of any combination of scalar arguments or array values;
1624 the array values will be included in the list as if each individual element were
1625 interpolated at that point in the list, forming a longer single-dimensional
1627 Elements of the LIST should be separated by commas.
1628 If an operation is listed both with and without parentheses around its
1629 arguments, it means you can either use it as a unary operator or
1631 To use it as a function call, the next token on the same line must
1632 be a left parenthesis.
1633 (There may be intervening white space.)
1634 Such a function then has highest precedence, as you would expect from
1636 If any token other than a left parenthesis follows, then it is a
1637 unary operator, with a precedence depending only on whether it is a LIST
1639 LIST operators have lowest precedence.
1640 All other unary operators have a precedence greater than relational operators
1641 but less than arithmetic operators.
1642 See the section on Precedence.
1646 This is just like the /pattern/ search, except that it matches only once between
1650 This is a useful optimization when you only want to see the first occurrence of
1651 something in each file of a set of files, for instance.
1652 Only ?? patterns local to the current package are reset.
1653 .Ip "accept(NEWSOCKET,GENERICSOCKET)" 8 2
1654 Does the same thing that the accept system call does.
1655 Returns true if it succeeded, false otherwise.
1656 See example in section on Interprocess Communication.
1657 .Ip "alarm(SECONDS)" 8 4
1658 .Ip "alarm SECONDS" 8
1659 Arranges to have a SIGALRM delivered to this process after the specified number
1660 of seconds (minus 1, actually) have elapsed. Thus, alarm(15) will cause
1661 a SIGALRM at some point more than 14 seconds in the future.
1662 Only one timer may be counting at once. Each call disables the previous
1663 timer, and an argument of 0 may be supplied to cancel the previous timer
1664 without starting a new one.
1665 The returned value is the amount of time remaining on the previous timer.
1666 .Ip "atan2(Y,X)" 8 2
1667 Returns the arctangent of Y/X in the range
1668 .if t \-\(*p to \(*p.
1670 .Ip "bind(SOCKET,NAME)" 8 2
1671 Does the same thing that the bind system call does.
1672 Returns true if it succeeded, false otherwise.
1673 NAME should be a packed address of the proper type for the socket.
1674 See example in section on Interprocess Communication.
1675 .Ip "binmode(FILEHANDLE)" 8 4
1676 .Ip "binmode FILEHANDLE" 8 4
1677 Arranges for the file to be read in \*(L"binary\*(R" mode in operating systems
1678 that distinguish between binary and text files.
1679 Files that are not read in binary mode have CR LF sequences translated
1680 to LF on input and LF translated to CR LF on output.
1681 Binmode has no effect under Unix.
1682 If FILEHANDLE is an expression, the value is taken as the name of
1686 Returns the context of the current subroutine call:
1689 ($package,$filename,$line) = caller;
1692 With EXPR, returns some extra information that the debugger uses to print
1693 a stack trace. The value of EXPR indicates how many call frames to go
1694 back before the current one.
1695 .Ip "chdir(EXPR)" 8 2
1696 .Ip "chdir EXPR" 8 2
1697 Changes the working directory to EXPR, if possible.
1698 If EXPR is omitted, changes to home directory.
1699 Returns 1 upon success, 0 otherwise.
1702 .Ip "chmod(LIST)" 8 2
1703 .Ip "chmod LIST" 8 2
1704 Changes the permissions of a list of files.
1705 The first element of the list must be the numerical mode.
1706 Returns the number of files successfully changed.
1710 $cnt = chmod 0755, \'foo\', \'bar\';
1711 chmod 0755, @executables;
1714 .Ip "chop(LIST)" 8 7
1715 .Ip "chop(VARIABLE)" 8
1716 .Ip "chop VARIABLE" 8
1718 Chops off the last character of a string and returns the character chopped.
1719 It's used primarily to remove the newline from the end of an input record,
1720 but is much more efficient than s/\en// because it neither scans nor copies
1722 If VARIABLE is omitted, chops $_.
1728 chop; # avoid \en on last field
1729 @array = split(/:/);
1734 You can actually chop anything that's an lvalue, including an assignment:
1737 chop($cwd = \`pwd\`);
1738 chop($answer = <STDIN>);
1741 If you chop a list, each element is chopped.
1742 Only the value of the last chop is returned.
1743 .Ip "chown(LIST)" 8 2
1744 .Ip "chown LIST" 8 2
1745 Changes the owner (and group) of a list of files.
1746 The first two elements of the list must be the NUMERICAL uid and gid,
1748 Returns the number of files successfully changed.
1752 $cnt = chown $uid, $gid, \'foo\', \'bar\';
1753 chown $uid, $gid, @filenames;
1757 Here's an example that looks up non-numeric uids in the passwd file:
1767 open(pass, \'/etc/passwd\') || die "Can't open passwd: $!\en";
1770 open(pass, \'/etc/passwd\')
1771 || die "Can't open passwd: $!\en";
1774 ($login,$pass,$uid,$gid) = split(/:/);
1775 $uid{$login} = $uid;
1776 $gid{$login} = $gid;
1778 @ary = <${pattern}>; # get filenames
1779 if ($uid{$user} eq \'\') {
1780 die "$user not in passwd file";
1783 chown $uid{$user}, $gid{$user}, @ary;
1787 .Ip "chroot(FILENAME)" 8 5
1788 .Ip "chroot FILENAME" 8
1789 Does the same as the system call of that name.
1790 If you don't know what it does, don't worry about it.
1791 If FILENAME is omitted, does chroot to $_.
1792 .Ip "close(FILEHANDLE)" 8 5
1793 .Ip "close FILEHANDLE" 8
1794 Closes the file or pipe associated with the file handle.
1795 You don't have to close FILEHANDLE if you are immediately going to
1796 do another open on it, since open will close it for you.
1799 However, an explicit close on an input file resets the line counter ($.), while
1800 the implicit close done by
1803 Also, closing a pipe will wait for the process executing on the pipe to complete,
1804 in case you want to look at the output of the pipe afterwards.
1805 Closing a pipe explicitly also puts the status value of the command into $?.
1810 open(OUTPUT, \'|sort >foo\'); # pipe to sort
1811 .\|.\|. # print stuff to output
1812 close OUTPUT; # wait for sort to finish
1813 open(INPUT, \'foo\'); # get sort's results
1816 FILEHANDLE may be an expression whose value gives the real filehandle name.
1817 .Ip "closedir(DIRHANDLE)" 8 5
1818 .Ip "closedir DIRHANDLE" 8
1819 Closes a directory opened by opendir().
1820 .Ip "connect(SOCKET,NAME)" 8 2
1821 Does the same thing that the connect system call does.
1822 Returns true if it succeeded, false otherwise.
1823 NAME should be a package address of the proper type for the socket.
1824 See example in section on Interprocess Communication.
1827 Returns the cosine of EXPR (expressed in radians).
1828 If EXPR is omitted takes cosine of $_.
1829 .Ip "crypt(PLAINTEXT,SALT)" 8 6
1830 Encrypts a string exactly like the crypt() function in the C library.
1831 Useful for checking the password file for lousy passwords.
1832 Only the guys wearing white hats should do this.
1833 .Ip "dbmclose(ASSOC_ARRAY)" 8 6
1834 .Ip "dbmclose ASSOC_ARRAY" 8
1835 Breaks the binding between a dbm file and an associative array.
1836 The values remaining in the associative array are meaningless unless
1837 you happen to want to know what was in the cache for the dbm file.
1838 This function is only useful if you have ndbm.
1839 .Ip "dbmopen(ASSOC,DBNAME,MODE)" 8 6
1840 This binds a dbm or ndbm file to an associative array.
1841 ASSOC is the name of the associative array.
1842 (Unlike normal open, the first argument is NOT a filehandle, even though
1844 DBNAME is the name of the database (without the .dir or .pag extension).
1845 If the database does not exist, it is created with protection specified
1846 by MODE (as modified by the umask).
1847 If your system only supports the older dbm functions, you may only have one
1848 dbmopen in your program.
1849 If your system has neither dbm nor ndbm, calling dbmopen produces a fatal
1852 Values assigned to the associative array prior to the dbmopen are lost.
1853 A certain number of values from the dbm file are cached in memory.
1854 By default this number is 64, but you can increase it by preallocating
1855 that number of garbage entries in the associative array before the dbmopen.
1856 You can flush the cache if necessary with the reset command.
1858 If you don't have write access to the dbm file, you can only read
1859 associative array variables, not set them.
1860 If you want to test whether you can write, either use file tests or
1861 try setting a dummy array entry inside an eval, which will trap the error.
1863 Note that functions such as keys() and values() may return huge array values
1864 when used on large dbm files.
1865 You may prefer to use the each() function to iterate over large dbm files.
1870 # print out history file offsets
1871 dbmopen(HIST,'/usr/lib/news/history',0666);
1872 while (($key,$val) = each %HIST) {
1873 print $key, ' = ', unpack('L',$val), "\en";
1878 .Ip "defined(EXPR)" 8 6
1879 .Ip "defined EXPR" 8
1880 Returns a boolean value saying whether the lvalue EXPR has a real value
1882 Many operations return the undefined value under exceptional conditions,
1883 such as end of file, uninitialized variable, system error and such.
1884 This function allows you to distinguish between an undefined null string
1885 and a defined null string with operations that might return a real null
1886 string, in particular referencing elements of an array.
1887 You may also check to see if arrays or subroutines exist.
1888 Use on predefined variables is not guaranteed to produce intuitive results.
1893 print if defined $switch{'D'};
1894 print "$val\en" while defined($val = pop(@ary));
1895 die "Can't readlink $sym: $!"
1896 unless defined($value = readlink $sym);
1897 eval '@foo = ()' if defined(@foo);
1898 die "No XYZ package defined" unless defined %_XYZ;
1899 sub foo { defined &bar ? &bar(@_) : die "No bar"; }
1903 .Ip "delete $ASSOC{KEY}" 8 6
1904 Deletes the specified value from the specified associative array.
1905 Returns the deleted value, or the undefined value if nothing was deleted.
1906 Deleting from $ENV{} modifies the environment.
1907 Deleting from an array bound to a dbm file deletes the entry from the dbm
1910 The following deletes all the values of an associative array:
1914 foreach $key (keys %ARRAY) {
1915 delete $ARRAY{$key};
1919 (But it would be faster to use the
1922 Saying undef %ARRAY is faster yet.)
1925 Outside of an eval, prints the value of LIST to
1927 and exits with the current value of $!
1929 If $! is 0, exits with the value of ($? >> 8) (\`command\` status).
1930 If ($? >> 8) is 0, exits with 255.
1931 Inside an eval, the error message is stuffed into $@ and the eval is terminated
1932 with the undefined value.
1934 Equivalent examples:
1939 die "Can't cd to spool: $!\en" unless chdir \'/usr/spool/news\';
1942 die "Can't cd to spool: $!\en"
1943 unless chdir \'/usr/spool/news\';
1946 chdir \'/usr/spool/news\' || die "Can't cd to spool: $!\en"
1950 If the value of EXPR does not end in a newline, the current script line
1951 number and input line number (if any) are also printed, and a newline is
1953 Hint: sometimes appending \*(L", stopped\*(R" to your message will cause it to make
1954 better sense when the string \*(L"at foo line 123\*(R" is appended.
1955 Suppose you are running script \*(L"canasta\*(R".
1959 die "/etc/games is no good";
1960 die "/etc/games is no good, stopped";
1962 produce, respectively
1964 /etc/games is no good at canasta line 123.
1965 /etc/games is no good, stopped at canasta line 123.
1971 Returns the value of the last command in the sequence of commands indicated
1973 When modified by a loop modifier, executes the BLOCK once before testing the
1975 (On other statements the loop modifiers test the conditional first.)
1976 .Ip "do SUBROUTINE (LIST)" 8 3
1977 Executes a SUBROUTINE declared by a
1979 declaration, and returns the value
1980 of the last expression evaluated in SUBROUTINE.
1981 If there is no subroutine by that name, produces a fatal error.
1982 (You may use the \*(L"defined\*(R" operator to determine if a subroutine
1984 If you pass arrays as part of LIST you may wish to pass the length
1985 of the array in front of each array.
1986 (See the section on subroutines later on.)
1987 SUBROUTINE may be a scalar variable, in which case the variable contains
1988 the name of the subroutine to execute.
1989 The parentheses are required to avoid confusion with the \*(L"do EXPR\*(R"
1992 As an alternate form, you may call a subroutine by prefixing the name with
1993 an ampersand: &foo(@args).
1994 If you aren't passing any arguments, you don't have to use parentheses.
1995 If you omit the parentheses, no @_ array is passed to the subroutine.
1996 The & form is also used to specify subroutines to the defined and undef
1999 Uses the value of EXPR as a filename and executes the contents of the file
2003 Its primary use is to include subroutines from a
2012 eval \`cat stat.pl\`;
2015 except that it's more efficient, more concise, keeps track of the current
2016 filename for error messages, and searches all the
2018 libraries if the file
2019 isn't in the current directory (see also the @INC array in Predefined Names).
2020 It's the same, however, in that it does reparse the file every time you
2021 call it, so if you are going to use the file inside a loop you might prefer
2022 to use \-P and #include, at the expense of a little more startup time.
2023 (The main problem with #include is that cpp doesn't grok # comments\*(--a
2024 workaround is to use \*(L";#\*(R" for standalone comments.)
2025 Note that the following are NOT equivalent:
2029 do $foo; # eval a file
2030 do $foo(); # call a subroutine
2033 Note that inclusion of library routines is better done with
2034 the \*(L"require\*(R" operator.
2035 .Ip "dump LABEL" 8 6
2036 This causes an immediate core dump.
2037 Primarily this is so that you can use the undump program to turn your
2038 core dump into an executable binary after having initialized all your
2039 variables at the beginning of the program.
2040 When the new binary is executed it will begin by executing a "goto LABEL"
2041 (with all the restrictions that goto suffers).
2042 Think of it as a goto with an intervening core dump and reincarnation.
2043 If LABEL is omitted, restarts the program from the top.
2044 WARNING: any files opened at the time of the dump will NOT be open any more
2045 when the program is reincarnated, with possible resulting confusion on the part
2054 require 'getopt.pl';
2065 dump QUICKSTART if $ARGV[0] eq '-d';
2071 .Ip "each(ASSOC_ARRAY)" 8 6
2072 .Ip "each ASSOC_ARRAY" 8
2073 Returns a 2 element array consisting of the key and value for the next
2074 value of an associative array, so that you can iterate over it.
2075 Entries are returned in an apparently random order.
2076 When the array is entirely read, a null array is returned (which when
2077 assigned produces a FALSE (0) value).
2078 The next call to each() after that will start iterating again.
2079 The iterator can be reset only by reading all the elements from the array.
2080 You must not modify the array while iterating over it.
2081 There is a single iterator for each associative array, shared by all
2082 each(), keys() and values() function calls in the program.
2083 The following prints out your environment like the printenv program, only
2084 in a different order:
2088 while (($key,$value) = each %ENV) {
2089 print "$key=$value\en";
2093 See also keys() and values().
2094 .Ip "eof(FILEHANDLE)" 8 8
2097 Returns 1 if the next read on FILEHANDLE will return end of file, or if
2098 FILEHANDLE is not open.
2099 FILEHANDLE may be an expression whose value gives the real filehandle name.
2100 (Note that this function actually reads a character and then ungetc's it,
2101 so it is not very useful in an interactive context.)
2102 An eof without an argument returns the eof status for the last file read.
2103 Empty parentheses () may be used to indicate the pseudo file formed of the
2104 files listed on the command line, i.e. eof() is reasonable to use inside
2105 a while (<>) loop to detect the end of only the last file.
2106 Use eof(ARGV) or eof without the parentheses to test EACH file in a while (<>) loop.
2111 # insert dashes just before last line of last file
2114 print "\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\|\-\en";
2120 # reset line numbering on each input file
2123 if (eof) { # Not eof().
2129 .Ip "eval(EXPR)" 8 6
2131 EXPR is parsed and executed as if it were a little
2134 It is executed in the context of the current
2137 any variable settings, subroutine or format definitions remain afterwards.
2138 The value returned is the value of the last expression evaluated, just
2139 as with subroutines.
2140 If there is a syntax error or runtime error, or a die statement is
2141 executed, an undefined value is returned by
2142 eval, and $@ is set to the error message.
2143 If there was no error, $@ is guaranteed to be a null string.
2144 If EXPR is omitted, evaluates $_.
2145 The final semicolon, if any, may be omitted from the expression.
2147 Note that, since eval traps otherwise-fatal errors, it is useful for
2148 determining whether a particular feature
2149 (such as dbmopen or symlink) is implemented.
2150 It is also Perl's exception trapping mechanism, where the die operator is
2151 used to raise exceptions.
2152 .Ip "exec(LIST)" 8 8
2154 If there is more than one argument in LIST, or if LIST is an array with
2155 more than one value,
2156 calls execvp() with the arguments in LIST.
2157 If there is only one scalar argument, the argument is checked for shell metacharacters.
2158 If there are any, the entire argument is passed to \*(L"/bin/sh \-c\*(R" for parsing.
2159 If there are none, the argument is split into words and passed directly to
2160 execvp(), which is more efficient.
2161 Note: exec (and system) do not flush your output buffer, so you may need to
2162 set $| to avoid lost output.
2166 exec \'/bin/echo\', \'Your arguments are: \', @ARGV;
2167 exec "sort $outfile | uniq";
2171 If you don't really want to execute the first argument, but want to lie
2172 to the program you are executing about its own name, you can specify
2173 the program you actually want to run by assigning that to a variable and
2174 putting the name of the variable in front of the LIST without a comma.
2175 (This always forces interpretation of the LIST as a multi-valued list, even
2176 if there is only a single scalar in the list.)
2181 $shell = '/bin/csh';
2182 exec $shell '-sh'; # pretend it's a login shell
2185 .Ip "exit(EXPR)" 8 6
2187 Evaluates EXPR and exits immediately with that value.
2193 exit 0 \|if \|$ans \|=~ \|/\|^[Xx]\|/\|;
2198 If EXPR is omitted, exits with 0 status.
2203 to the power of EXPR.
2204 If EXPR is omitted, gives exp($_).
2205 .Ip "fcntl(FILEHANDLE,FUNCTION,SCALAR)" 8 4
2206 Implements the fcntl(2) function.
2207 You'll probably have to say
2210 require "fcntl.ph"; # probably /usr/local/lib/perl/fcntl.ph
2213 first to get the correct function definitions.
2214 If fcntl.ph doesn't exist or doesn't have the correct definitions
2216 your own, based on your C header files such as <sys/fcntl.h>.
2217 (There is a perl script called h2ph that comes with the perl kit
2218 which may help you in this.)
2219 Argument processing and value return works just like ioctl below.
2220 Note that fcntl will produce a fatal error if used on a machine that doesn't implement
2222 .Ip "fileno(FILEHANDLE)" 8 4
2223 .Ip "fileno FILEHANDLE" 8 4
2224 Returns the file descriptor for a filehandle.
2225 Useful for constructing bitmaps for select().
2226 If FILEHANDLE is an expression, the value is taken as the name of
2228 .Ip "flock(FILEHANDLE,OPERATION)" 8 4
2229 Calls flock(2) on FILEHANDLE.
2230 See manual page for flock(2) for definition of OPERATION.
2231 Returns true for success, false on failure.
2232 Will produce a fatal error if used on a machine that doesn't implement
2234 Here's a mailbox appender for BSD systems.
2244 flock(MBOX,$LOCK_EX);
2245 # and, in case someone appended
2246 # while we were waiting...
2251 flock(MBOX,$LOCK_UN);
2254 open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
2255 || die "Can't open mailbox: $!";
2258 print MBOX $msg,"\en\en";
2264 Returns the child pid to the parent process and 0 to the child process.
2265 Note: unflushed buffers remain unflushed in both processes, which means
2266 you may need to set $| to avoid duplicate output.
2267 .Ip "getc(FILEHANDLE)" 8 4
2268 .Ip "getc FILEHANDLE" 8
2270 Returns the next character from the input file attached to FILEHANDLE, or
2271 a null string at EOF.
2272 If FILEHANDLE is omitted, reads from STDIN.
2274 Returns the current login from /etc/utmp, if any.
2275 If null, use getpwuid.
2277 $login = getlogin || (getpwuid($<))[0] || "Somebody";
2279 .Ip "getpeername(SOCKET)" 8 3
2280 Returns the packed sockaddr address of other end of the SOCKET connection.
2284 # An internet sockaddr
2285 $sockaddr = 'S n a4 x8';
2286 $hersockaddr = getpeername(S);
2288 ($family, $port, $heraddr) = unpack($sockaddr,$hersockaddr);
2291 ($family, $port, $heraddr) =
2292 unpack($sockaddr,$hersockaddr);
2296 .Ip "getpgrp(PID)" 8 4
2298 Returns the current process group for the specified PID, 0 for the current
2300 Will produce a fatal error if used on a machine that doesn't implement
2302 If EXPR is omitted, returns process group of current process.
2304 Returns the process id of the parent process.
2305 .Ip "getpriority(WHICH,WHO)" 8 4
2306 Returns the current priority for a process, a process group, or a user.
2307 (See getpriority(2).)
2308 Will produce a fatal error if used on a machine that doesn't implement
2310 .Ip "getpwnam(NAME)" 8
2311 .Ip "getgrnam(NAME)" 8
2312 .Ip "gethostbyname(NAME)" 8
2313 .Ip "getnetbyname(NAME)" 8
2314 .Ip "getprotobyname(NAME)" 8
2315 .Ip "getpwuid(UID)" 8
2316 .Ip "getgrgid(GID)" 8
2317 .Ip "getservbyname(NAME,PROTO)" 8
2318 .Ip "gethostbyaddr(ADDR,ADDRTYPE)" 8
2319 .Ip "getnetbyaddr(ADDR,ADDRTYPE)" 8
2320 .Ip "getprotobynumber(NUMBER)" 8
2321 .Ip "getservbyport(PORT,PROTO)" 8
2330 .Ip "sethostent(STAYOPEN)" 8
2331 .Ip "setnetent(STAYOPEN)" 8
2332 .Ip "setprotoent(STAYOPEN)" 8
2333 .Ip "setservent(STAYOPEN)" 8
2340 These routines perform the same functions as their counterparts in the
2342 The return values from the various get routines are as follows:
2345 ($name,$passwd,$uid,$gid,
2346 $quota,$comment,$gcos,$dir,$shell) = getpw.\|.\|.
2347 ($name,$passwd,$gid,$members) = getgr.\|.\|.
2348 ($name,$aliases,$addrtype,$length,@addrs) = gethost.\|.\|.
2349 ($name,$aliases,$addrtype,$net) = getnet.\|.\|.
2350 ($name,$aliases,$proto) = getproto.\|.\|.
2351 ($name,$aliases,$port,$proto) = getserv.\|.\|.
2354 The $members value returned by getgr.\|.\|. is a space separated list
2355 of the login names of the members of the group.
2357 The @addrs value returned by the gethost.\|.\|. functions is a list of the
2358 raw addresses returned by the corresponding system library call.
2359 In the Internet domain, each address is four bytes long and you can unpack
2360 it by saying something like:
2363 ($a,$b,$c,$d) = unpack('C4',$addr[0]);
2366 .Ip "getsockname(SOCKET)" 8 3
2367 Returns the packed sockaddr address of this end of the SOCKET connection.
2371 # An internet sockaddr
2372 $sockaddr = 'S n a4 x8';
2373 $mysockaddr = getsockname(S);
2375 ($family, $port, $myaddr) = unpack($sockaddr,$mysockaddr);
2378 ($family, $port, $myaddr) =
2379 unpack($sockaddr,$mysockaddr);
2383 .Ip "getsockopt(SOCKET,LEVEL,OPTNAME)" 8 3
2384 Returns the socket option requested, or undefined if there is an error.
2385 .Ip "gmtime(EXPR)" 8 4
2387 Converts a time as returned by the time function to a 9-element array with
2388 the time analyzed for the Greenwich timezone.
2389 Typically used as follows:
2394 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = gmtime(time);
2397 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
2402 All array elements are numeric, and come straight out of a struct tm.
2403 In particular this means that $mon has the range 0.\|.11 and $wday has the
2405 If EXPR is omitted, does gmtime(time).
2406 .Ip "goto LABEL" 8 6
2407 Finds the statement labeled with LABEL and resumes execution there.
2408 Currently you may only go to statements in the main body of the program
2409 that are not nested inside a do {} construct.
2410 This statement is not implemented very efficiently, and is here only to make
2414 I may change its semantics at any time, consistent with support for translated
2417 Use it at your own risk.
2418 Better yet, don't use it at all.
2419 .Ip "grep(EXPR,LIST)" 8 4
2420 Evaluates EXPR for each element of LIST (locally setting $_ to each element)
2421 and returns the array value consisting of those elements for which the
2422 expression evaluated to true.
2423 In a scalar context, returns the number of times the expression was true.
2426 @foo = grep(!/^#/, @bar); # weed out comments
2429 Note that, since $_ is a reference into the array value, it can be
2430 used to modify the elements of the array.
2431 While this is useful and supported, it can cause bizarre results if
2432 the LIST is not a named array.
2435 Returns the decimal value of EXPR interpreted as an hex string.
2436 (To interpret strings that might start with 0 or 0x see oct().)
2437 If EXPR is omitted, uses $_.
2438 .Ip "index(STR,SUBSTR,POSITION)" 8 4
2439 .Ip "index(STR,SUBSTR)" 8 4
2440 Returns the position of the first occurrence of SUBSTR in STR at or after
2442 If POSITION is omitted, starts searching from the beginning of the string.
2443 The return value is based at 0, or whatever you've
2444 set the $[ variable to.
2445 If the substring is not found, returns one less than the base, ordinarily \-1.
2448 Returns the integer portion of EXPR.
2449 If EXPR is omitted, uses $_.
2450 .Ip "ioctl(FILEHANDLE,FUNCTION,SCALAR)" 8 4
2451 Implements the ioctl(2) function.
2452 You'll probably have to say
2455 require "ioctl.ph"; # probably /usr/local/lib/perl/ioctl.ph
2458 first to get the correct function definitions.
2459 If ioctl.ph doesn't exist or doesn't have the correct definitions
2461 your own, based on your C header files such as <sys/ioctl.h>.
2462 (There is a perl script called h2ph that comes with the perl kit
2463 which may help you in this.)
2464 SCALAR will be read and/or written depending on the FUNCTION\*(--a pointer
2465 to the string value of SCALAR will be passed as the third argument of
2466 the actual ioctl call.
2467 (If SCALAR has no string value but does have a numeric value, that value
2468 will be passed rather than a pointer to the string value.
2469 To guarantee this to be true, add a 0 to the scalar before using it.)
2470 The pack() and unpack() functions are useful for manipulating the values
2471 of structures used by ioctl().
2472 The following example sets the erase character to DEL.
2477 $sgttyb_t = "ccccs"; # 4 chars and a short
2478 if (ioctl(STDIN,$TIOCGETP,$sgttyb)) {
2479 @ary = unpack($sgttyb_t,$sgttyb);
2481 $sgttyb = pack($sgttyb_t,@ary);
2482 ioctl(STDIN,$TIOCSETP,$sgttyb)
2483 || die "Can't ioctl: $!";
2487 The return value of ioctl (and fcntl) is as follows:
2491 if OS returns:\h'|3i'perl returns:
2492 -1\h'|3i' undefined value
2493 0\h'|3i' string "0 but true"
2494 anything else\h'|3i' that number
2497 Thus perl returns true on success and false on failure, yet you can still
2498 easily determine the actual value returned by the operating system:
2501 ($retval = ioctl(...)) || ($retval = -1);
2502 printf "System returned %d\en", $retval;
2504 .Ip "join(EXPR,LIST)" 8 8
2505 .Ip "join(EXPR,ARRAY)" 8
2506 Joins the separate strings of LIST or ARRAY into a single string with fields
2507 separated by the value of EXPR, and returns the string.
2512 $_ = join(\|\':\', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
2516 $login,$passwd,$uid,$gid,$gcos,$home,$shell);
2522 .Ip "keys(ASSOC_ARRAY)" 8 6
2523 .Ip "keys ASSOC_ARRAY" 8
2524 Returns a normal array consisting of all the keys of the named associative
2526 The keys are returned in an apparently random order, but it is the same order
2527 as either the values() or each() function produces (given that the associative array
2528 has not been modified).
2529 Here is yet another way to print your environment:
2534 @values = values %ENV;
2535 while ($#keys >= 0) {
2536 print pop(@keys), \'=\', pop(@values), "\en";
2539 or how about sorted by key:
2542 foreach $key (sort(keys %ENV)) {
2543 print $key, \'=\', $ENV{$key}, "\en";
2547 .Ip "kill(LIST)" 8 8
2549 Sends a signal to a list of processes.
2550 The first element of the list must be the signal to send.
2551 Returns the number of processes successfully signaled.
2554 $cnt = kill 1, $child1, $child2;
2558 If the signal is negative, kills process groups instead of processes.
2559 (On System V, a negative \fIprocess\fR number will also kill process groups,
2560 but that's not portable.)
2561 You may use a signal name in quotes.
2562 .Ip "last LABEL" 8 8
2568 statement in C (as used in loops); it immediately exits the loop in question.
2569 If the LABEL is omitted, the command refers to the innermost enclosing loop.
2572 block, if any, is not executed:
2576 line: while (<STDIN>) {
2577 last line if /\|^$/; # exit when done with header
2582 .Ip "length(EXPR)" 8 4
2584 Returns the length in characters of the value of EXPR.
2585 If EXPR is omitted, returns length of $_.
2586 .Ip "link(OLDFILE,NEWFILE)" 8 2
2587 Creates a new filename linked to the old filename.
2588 Returns 1 for success, 0 otherwise.
2589 .Ip "listen(SOCKET,QUEUESIZE)" 8 2
2590 Does the same thing that the listen system call does.
2591 Returns true if it succeeded, false otherwise.
2592 See example in section on Interprocess Communication.
2593 .Ip "local(LIST)" 8 4
2594 Declares the listed variables to be local to the enclosing block,
2595 subroutine, eval or \*(L"do\*(R".
2596 All the listed elements must be legal lvalues.
2597 This operator works by saving the current values of those variables in LIST
2598 on a hidden stack and restoring them upon exiting the block, subroutine or eval.
2599 This means that called subroutines can also reference the local variable,
2600 but not the global one.
2601 The LIST may be assigned to if desired, which allows you to initialize
2602 your local variables.
2603 (If no initializer is given for a particular variable, it is created with
2604 an undefined value.)
2605 Commonly this is used to name the parameters to a subroutine.
2611 local($min, $max, $thunk) = @_;
2612 local($result) = \'\';
2615 # Presumably $thunk makes reference to $i
2617 for ($i = $min; $i < $max; $i++) {
2618 $result .= eval $thunk;
2625 if ($sw eq \'-v\') {
2626 # init local array with global array
2627 local(@ARGV) = @ARGV;
2628 unshift(@ARGV,\'echo\');
2634 # temporarily add to digits associative array
2636 # (NOTE: not claiming this is efficient!)
2637 local(%digits) = (%digits,'t',10,'e',11);
2642 Note that local() is a run-time command, and so gets executed every time
2643 through a loop, using up more stack storage each time until it's all
2644 released at once when the loop is exited.
2645 .Ip "localtime(EXPR)" 8 4
2646 .Ip "localtime EXPR" 8
2647 Converts a time as returned by the time function to a 9-element array with
2648 the time analyzed for the local timezone.
2649 Typically used as follows:
2654 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);
2657 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
2662 All array elements are numeric, and come straight out of a struct tm.
2663 In particular this means that $mon has the range 0.\|.11 and $wday has the
2665 If EXPR is omitted, does localtime(time).
2668 Returns logarithm (base
2671 If EXPR is omitted, returns log of $_.
2672 .Ip "lstat(FILEHANDLE)" 8 6
2673 .Ip "lstat FILEHANDLE" 8
2675 .Ip "lstat SCALARVARIABLE" 8
2676 Does the same thing as the stat() function, but stats a symbolic link
2677 instead of the file the symbolic link points to.
2678 If symbolic links are unimplemented on your system, a normal stat is done.
2679 .Ip "m/PATTERN/gio" 8 4
2680 .Ip "/PATTERN/gio" 8
2681 Searches a string for a pattern match, and returns true (1) or false (\'\').
2682 If no string is specified via the =~ or !~ operator,
2683 the $_ string is searched.
2684 (The string specified with =~ need not be an lvalue\*(--it may be the result of an expression evaluation, but remember the =~ binds rather tightly.)
2685 See also the section on regular expressions.
2687 If / is the delimiter then the initial \*(L'm\*(R' is optional.
2688 With the \*(L'm\*(R' you can use any pair of non-alphanumeric characters
2690 This is particularly useful for matching Unix path names that contain \*(L'/\*(R'.
2691 If the final delimiter is followed by the optional letter \*(L'i\*(R', the matching is
2692 done in a case-insensitive manner.
2693 PATTERN may contain references to scalar variables, which will be interpolated
2694 (and the pattern recompiled) every time the pattern search is evaluated.
2695 (Note that $) and $| may not be interpolated because they look like end-of-string tests.)
2696 If you want such a pattern to be compiled only once, add an \*(L"o\*(R" after
2697 the trailing delimiter.
2698 This avoids expensive run-time recompilations, and
2699 is useful when the value you are interpolating won't change over the
2701 If the PATTERN evaluates to a null string, the most recent successful
2702 regular expression is used instead.
2704 If used in a context that requires an array value, a pattern match returns an
2705 array consisting of the subexpressions matched by the parentheses in the
2707 i.e. ($1, $2, $3.\|.\|.).
2708 It does NOT actually set $1, $2, etc. in this case, nor does it set $+, $`, $&
2710 If the match fails, a null array is returned.
2711 If the match succeeds, but there were no parentheses, an array value of (1)
2718 open(tty, \'/dev/tty\');
2719 <tty> \|=~ \|/\|^y\|/i \|&& \|do foo(\|); # do foo if desired
2721 if (/Version: \|*\|([0\-9.]*\|)\|/\|) { $version = $1; }
2723 next if m#^/usr/spool/uucp#;
2729 print if /$arg/o; # compile only once
2732 if (($F1, $F2, $Etc) = ($foo =~ /^(\eS+)\es+(\eS+)\es*(.*)/))
2735 This last example splits $foo into the first two words and the remainder
2736 of the line, and assigns those three fields to $F1, $F2 and $Etc.
2737 The conditional is true if any variables were assigned, i.e. if the pattern
2740 The \*(L"g\*(R" modifier specifies global pattern matching\*(--that is,
2741 matching as many times as possible within the string. How it behaves
2742 depends on the context. In an array context, it returns a list of
2743 all the substrings matched by all the parentheses in the regular expression.
2744 If there are no parentheses, it returns a list of all the matched strings,
2745 as if there were parentheses around the whole pattern. In a scalar context,
2746 it iterates through the string, returning TRUE each time it matches, and
2747 FALSE when it eventually runs out of matches. (In other words, it remembers
2748 where it left off last time and restarts the search at that point.) It
2749 presumes that you have not modified the string since the last match.
2750 Modifying the string between matches may result in undefined behavior.
2751 (You can actually get away with in-place modifications via substr()
2752 that do not change the length of the entire string. In general, however,
2753 you should be using s///g for such modifications.) Examples:
2757 ($one,$five,$fifteen) = (\`uptime\` =~ /(\ed+\e.\ed+)/g);
2761 while ($paragraph = <>) {
2762 while ($paragraph =~ /[a-z][\'")]*[.!?]+[\'")]*\es/g) {
2766 print "$sentences\en";
2769 .Ip "mkdir(FILENAME,MODE)" 8 3
2770 Creates the directory specified by FILENAME, with permissions specified by
2771 MODE (as modified by umask).
2772 If it succeeds it returns 1, otherwise it returns 0 and sets $! (errno).
2773 .Ip "msgctl(ID,CMD,ARG)" 8 4
2774 Calls the System V IPC function msgctl. If CMD is &IPC_STAT, then ARG
2775 must be a variable which will hold the returned msqid_ds structure.
2776 Returns like ioctl: the undefined value for error, "0 but true" for
2777 zero, or the actual return value otherwise.
2778 .Ip "msgget(KEY,FLAGS)" 8 4
2779 Calls the System V IPC function msgget. Returns the message queue id,
2780 or the undefined value if there is an error.
2781 .Ip "msgsnd(ID,MSG,FLAGS)" 8 4
2782 Calls the System V IPC function msgsnd to send the message MSG to the
2783 message queue ID. MSG must begin with the long integer message type,
2784 which may be created with pack("L", $type). Returns true if
2785 successful, or false if there is an error.
2786 .Ip "msgrcv(ID,VAR,SIZE,TYPE,FLAGS)" 8 4
2787 Calls the System V IPC function msgrcv to receive a message from
2788 message queue ID into variable VAR with a maximum message size of
2789 SIZE. Note that if a message is received, the message type will be
2790 the first thing in VAR, and the maximum length of VAR is SIZE plus the
2791 size of the message type. Returns true if successful, or false if
2793 .Ip "next LABEL" 8 8
2799 statement in C; it starts the next iteration of the loop:
2803 line: while (<STDIN>) {
2804 next line if /\|^#/; # discard comments
2809 Note that if there were a
2811 block on the above, it would get executed even on discarded lines.
2812 If the LABEL is omitted, the command refers to the innermost enclosing loop.
2815 Returns the decimal value of EXPR interpreted as an octal string.
2816 (If EXPR happens to start off with 0x, interprets it as a hex string instead.)
2817 The following will handle decimal, octal and hex in the standard notation:
2820 $val = oct($val) if $val =~ /^0/;
2823 If EXPR is omitted, uses $_.
2824 .Ip "open(FILEHANDLE,EXPR)" 8 8
2825 .Ip "open(FILEHANDLE)" 8
2826 .Ip "open FILEHANDLE" 8
2827 Opens the file whose filename is given by EXPR, and associates it with
2829 If FILEHANDLE is an expression, its value is used as the name of the
2830 real filehandle wanted.
2831 If EXPR is omitted, the scalar variable of the same name as the FILEHANDLE
2832 contains the filename.
2833 If the filename begins with \*(L"<\*(R" or nothing, the file is opened for
2835 If the filename begins with \*(L">\*(R", the file is opened for output.
2836 If the filename begins with \*(L">>\*(R", the file is opened for appending.
2837 (You can put a \'+\' in front of the \'>\' or \'<\' to indicate that you
2838 want both read and write access to the file.)
2839 If the filename begins with \*(L"|\*(R", the filename is interpreted
2840 as a command to which output is to be piped, and if the filename ends
2841 with a \*(L"|\*(R", the filename is interpreted as command which pipes
2843 (You may not have a command that pipes both in and out.)
2844 Opening \'\-\' opens
2846 and opening \'>\-\' opens
2848 Open returns non-zero upon success, the undefined value otherwise.
2849 If the open involved a pipe, the return value happens to be the pid
2856 open article || die "Can't find article $article: $!\en";
2857 while (<article>) {\|.\|.\|.
2860 open(LOG, \'>>/usr/spool/news/twitlog\'\|); # (log is reserved)
2863 open(LOG, \'>>/usr/spool/news/twitlog\'\|);
2868 open(article, "caesar <$article |"\|); # decrypt article
2871 open(article, "caesar <$article |"\|);
2876 open(extract, "|sort >/tmp/Tmp$$"\|); # $$ is our process#
2879 open(extract, "|sort >/tmp/Tmp$$"\|);
2880 # $$ is our process#
2884 # process argument list of files along with any includes
2886 foreach $file (@ARGV) {
2887 do process($file, \'fh00\'); # no pun intended
2891 local($filename, $input) = @_;
2892 $input++; # this is a string increment
2893 unless (open($input, $filename)) {
2894 print STDERR "Can't open $filename: $!\en";
2898 while (<$input>) { # note the use of indirection
2901 while (<$input>) { # note use of indirection
2903 if (/^#include "(.*)"/) {
2904 do process($1, $input);
2912 You may also, in the Bourne shell tradition, specify an EXPR beginning
2913 with \*(L">&\*(R", in which case the rest of the string
2914 is interpreted as the name of a filehandle
2915 (or file descriptor, if numeric) which is to be duped and opened.
2916 You may use & after >, >>, <, +>, +>> and +<.
2917 The mode you specify should match the mode of the original filehandle.
2918 Here is a script that saves, redirects, and restores
2926 open(SAVEOUT, ">&STDOUT");
2927 open(SAVEERR, ">&STDERR");
2929 open(STDOUT, ">foo.out") || die "Can't redirect stdout";
2930 open(STDERR, ">&STDOUT") || die "Can't dup stdout";
2932 select(STDERR); $| = 1; # make unbuffered
2933 select(STDOUT); $| = 1; # make unbuffered
2935 print STDOUT "stdout 1\en"; # this works for
2936 print STDERR "stderr 1\en"; # subprocesses too
2941 open(STDOUT, ">&SAVEOUT");
2942 open(STDERR, ">&SAVEERR");
2944 print STDOUT "stdout 2\en";
2945 print STDERR "stderr 2\en";
2948 If you open a pipe on the command \*(L"\-\*(R", i.e. either \*(L"|\-\*(R" or \*(L"\-|\*(R",
2949 then there is an implicit fork done, and the return value of open
2950 is the pid of the child within the parent process, and 0 within the child
2952 (Use defined($pid) to determine if the open was successful.)
2953 The filehandle behaves normally for the parent, but i/o to that
2954 filehandle is piped from/to the
2956 of the child process.
2957 In the child process the filehandle isn't opened\*(--i/o happens from/to
2962 Typically this is used like the normal piped open when you want to exercise
2963 more control over just how the pipe command gets executed, such as when
2964 you are running setuid, and don't want to have to scan shell commands
2966 The following pairs are more or less equivalent:
2970 open(FOO, "|tr \'[a\-z]\' \'[A\-Z]\'");
2971 open(FOO, "|\-") || exec \'tr\', \'[a\-z]\', \'[A\-Z]\';
2973 open(FOO, "cat \-n '$file'|");
2974 open(FOO, "\-|") || exec \'cat\', \'\-n\', $file;
2977 Explicitly closing any piped filehandle causes the parent process to wait for the
2978 child to finish, and returns the status value in $?.
2979 Note: on any operation which may do a fork,
2980 unflushed buffers remain unflushed in both
2981 processes, which means you may need to set $| to
2982 avoid duplicate output.
2984 The filename that is passed to open will have leading and trailing
2986 In order to open a file with arbitrary weird characters in it, it's necessary
2987 to protect any leading and trailing whitespace thusly:
2991 $file =~ s#^(\es)#./$1#;
2992 open(FOO, "< $file\e0");
2995 .Ip "opendir(DIRHANDLE,EXPR)" 8 3
2996 Opens a directory named EXPR for processing by readdir(), telldir(), seekdir(),
2997 rewinddir() and closedir().
2998 Returns true if successful.
2999 DIRHANDLEs have their own namespace separate from FILEHANDLEs.
3002 Returns the numeric ascii value of the first character of EXPR.
3003 If EXPR is omitted, uses $_.
3004 ''' Comments on f & d by gnb@melba.bby.oz.au 22/11/89
3005 .Ip "pack(TEMPLATE,LIST)" 8 4
3006 Takes an array or list of values and packs it into a binary structure,
3007 returning the string containing the structure.
3008 The TEMPLATE is a sequence of characters that give the order and type
3009 of values, as follows:
3012 A An ascii string, will be space padded.
3013 a An ascii string, will be null padded.
3014 c A signed char value.
3015 C An unsigned char value.
3016 s A signed short value.
3017 S An unsigned short value.
3018 i A signed integer value.
3019 I An unsigned integer value.
3020 l A signed long value.
3021 L An unsigned long value.
3022 n A short in \*(L"network\*(R" order.
3023 N A long in \*(L"network\*(R" order.
3024 f A single-precision float in the native format.
3025 d A double-precision float in the native format.
3026 p A pointer to a string.
3029 @ Null fill to absolute position.
3030 u A uuencoded string.
3031 b A bit string (ascending bit order, like vec()).
3032 B A bit string (descending bit order).
3033 h A hex string (low nybble first).
3034 H A hex string (high nybble first).
3037 Each letter may optionally be followed by a number which gives a repeat
3039 With all types except "a", "A", "b", "B", "h" and "H",
3040 the pack function will gobble up that many values
3042 A * for the repeat count means to use however many items are left.
3043 The "a" and "A" types gobble just one value, but pack it as a string of length
3045 padding with nulls or spaces as necessary.
3046 (When unpacking, "A" strips trailing spaces and nulls, but "a" does not.)
3047 Likewise, the "b" and "B" fields pack a string that many bits long.
3048 The "h" and "H" fields pack a string that many nybbles long.
3049 Real numbers (floats and doubles) are in the native machine format
3050 only; due to the multiplicity of floating formats around, and the lack
3051 of a standard \*(L"network\*(R" representation, no facility for
3052 interchange has been made.
3053 This means that packed floating point data
3054 written on one machine may not be readable on another - even if both
3055 use IEEE floating point arithmetic (as the endian-ness of the memory
3056 representation is not part of the IEEE spec).
3058 doubles internally for all numeric calculation, and converting from
3059 double -> float -> double will lose precision (i.e. unpack("f",
3060 pack("f", $foo)) will not in general equal $foo).
3065 $foo = pack("cccc",65,66,67,68);
3067 $foo = pack("c4",65,66,67,68);
3070 $foo = pack("ccxxcc",65,66,67,68);
3071 # foo eq "AB\e0\e0CD"
3073 $foo = pack("s2",1,2);
3074 # "\e1\e0\e2\e0" on little-endian
3075 # "\e0\e1\e0\e2" on big-endian
3077 $foo = pack("a4","abcd","x","y","z");
3080 $foo = pack("aaaa","abcd","x","y","z");
3083 $foo = pack("a14","abcdefg");
3084 # "abcdefg\e0\e0\e0\e0\e0\e0\e0"
3086 $foo = pack("i9pl", gmtime);
3087 # a real struct tm (on my system anyway)
3090 unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
3093 The same template may generally also be used in the unpack function.
3094 .Ip "pipe(READHANDLE,WRITEHANDLE)" 8 3
3095 Opens a pair of connected pipes like the corresponding system call.
3096 Note that if you set up a loop of piped processes, deadlock can occur
3097 unless you are very careful.
3098 In addition, note that perl's pipes use stdio buffering, so you may need
3099 to set $| to flush your WRITEHANDLE after each command, depending on
3101 [Requires version 3.0 patchlevel 9.]
3104 Pops and returns the last value of the array, shortening the array by 1.
3105 Has the same effect as
3108 $tmp = $ARRAY[$#ARRAY\-\|\-];
3111 If there are no elements in the array, returns the undefined value.
3112 .Ip "print(FILEHANDLE LIST)" 8 10
3114 .Ip "print FILEHANDLE LIST" 8
3117 Prints a string or a comma-separated list of strings.
3118 Returns non-zero if successful.
3119 FILEHANDLE may be a scalar variable name, in which case the variable contains
3120 the name of the filehandle, thus introducing one level of indirection.
3121 (NOTE: If FILEHANDLE is a variable and the next token is a term, it may be
3122 misinterpreted as an operator unless you interpose a + or put parens around
3124 If FILEHANDLE is omitted, prints by default to standard output (or to the
3125 last selected output channel\*(--see select()).
3126 If LIST is also omitted, prints $_ to
3128 To set the default output channel to something other than
3130 use the select operation.
3131 Note that, because print takes a LIST, anything in the LIST is evaluated
3132 in an array context, and any subroutine that you call will have one or more
3133 of its expressions evaluated in an array context.
3134 Also be careful not to follow the print keyword with a left parenthesis
3135 unless you want the corresponding right parenthesis to terminate the
3136 arguments to the print\*(--interpose a + or put parens around all the arguments.
3137 .Ip "printf(FILEHANDLE LIST)" 8 10
3138 .Ip "printf(LIST)" 8
3139 .Ip "printf FILEHANDLE LIST" 8
3141 Equivalent to a \*(L"print FILEHANDLE sprintf(LIST)\*(R".
3142 .Ip "push(ARRAY,LIST)" 8 7
3143 Treats ARRAY (@ is optional) as a stack, and pushes the values of LIST
3144 onto the end of ARRAY.
3145 The length of ARRAY increases by the length of LIST.
3146 Has the same effect as
3150 $ARRAY[++$#ARRAY] = $value;
3154 but is more efficient.
3158 These are not really functions, but simply syntactic sugar to let you
3159 avoid putting too many backslashes into quoted strings.
3160 The q operator is a generalized single quote, and the qq operator a
3161 generalized double quote.
3162 The qx operator is a generalized backquote.
3163 Any non-alphanumeric delimiter can be used in place of /, including newline.
3164 If the delimiter is an opening bracket or parenthesis, the final delimiter
3165 will be the corresponding closing bracket or parenthesis.
3166 (Embedded occurrences of the closing bracket need to be backslashed as usual.)
3171 $foo = q!I said, "You said, \'She said it.\'"!;
3172 $bar = q(\'This is it.\');
3173 $today = qx{ date };
3175 *** The previous line contains the naughty word "$&".\en
3176 if /(ibm|apple|awk)/; # :-)
3179 .Ip "rand(EXPR)" 8 8
3182 Returns a random fractional number between 0 and the value of EXPR.
3183 (EXPR should be positive.)
3184 If EXPR is omitted, returns a value between 0 and 1.
3186 .Ip "read(FILEHANDLE,SCALAR,LENGTH,OFFSET)" 8 5
3187 .Ip "read(FILEHANDLE,SCALAR,LENGTH)" 8 5
3188 Attempts to read LENGTH bytes of data into variable SCALAR from the specified
3190 Returns the number of bytes actually read, or undef if there was an error.
3191 SCALAR will be grown or shrunk to the length actually read.
3192 An OFFSET may be specified to place the read data at some other place
3193 than the beginning of the string.
3194 This call is actually implemented in terms of stdio's fread call. To get
3195 a true read system call, see sysread.
3196 .Ip "readdir(DIRHANDLE)" 8 3
3197 .Ip "readdir DIRHANDLE" 8
3198 Returns the next directory entry for a directory opened by opendir().
3199 If used in an array context, returns all the rest of the entries in the
3201 If there are no more entries, returns an undefined value in a scalar context
3202 or a null list in an array context.
3203 .Ip "readlink(EXPR)" 8 6
3204 .Ip "readlink EXPR" 8
3205 Returns the value of a symbolic link, if symbolic links are implemented.
3206 If not, gives a fatal error.
3207 If there is some system error, returns the undefined value and sets $! (errno).
3208 If EXPR is omitted, uses $_.
3209 .Ip "recv(SOCKET,SCALAR,LEN,FLAGS)" 8 4
3210 Receives a message on a socket.
3211 Attempts to receive LENGTH bytes of data into variable SCALAR from the specified
3213 Returns the address of the sender, or the undefined value if there's an error.
3214 SCALAR will be grown or shrunk to the length actually read.
3215 Takes the same flags as the system call of the same name.
3216 .Ip "redo LABEL" 8 8
3220 command restarts the loop block without evaluating the conditional again.
3223 block, if any, is not executed.
3224 If the LABEL is omitted, the command refers to the innermost enclosing loop.
3225 This command is normally used by programs that want to lie to themselves
3226 about what was just input:
3230 # a simpleminded Pascal comment stripper
3231 # (warning: assumes no { or } in strings)
3232 line: while (<STDIN>) {
3233 while (s|\|({.*}.*\|){.*}|$1 \||) {}
3238 if (\|/\|}/\|) { # end of comment?
3248 .Ip "rename(OLDNAME,NEWNAME)" 8 2
3249 Changes the name of a file.
3250 Returns 1 for success, 0 otherwise.
3251 Will not work across filesystem boundaries.
3252 .Ip "require(EXPR)" 8 6
3253 .Ip "require EXPR" 8
3255 Includes the library file specified by EXPR, or by $_ if EXPR is not supplied.
3256 Has semantics similar to the following subroutine:
3260 local($filename) = @_;
3261 return 1 if $INC{$filename};
3262 local($realfilename,$result);
3264 foreach $prefix (@INC) {
3265 $realfilename = "$prefix/$filename";
3266 if (-f $realfilename) {
3267 $result = do $realfilename;
3271 die "Can't find $filename in \e@INC";
3274 die "$filename did not return true value" unless $result;
3275 $INC{$filename} = $realfilename;
3280 Note that the file will not be included twice under the same specified name.
3281 .Ip "reset(EXPR)" 8 6
3286 block at the end of a loop to clear variables and reset ?? searches
3287 so that they work again.
3288 The expression is interpreted as a list of single characters (hyphens allowed
3290 All variables and arrays beginning with one of those letters are reset to
3291 their pristine state.
3292 If the expression is omitted, one-match searches (?pattern?) are reset to
3294 Only resets variables or searches in the current package.
3300 reset \'X\'; \h'|2i'# reset all X variables
3301 reset \'a\-z\';\h'|2i'# reset lower case variables
3302 reset; \h'|2i'# just reset ?? searches
3305 Note: resetting \*(L"A\-Z\*(R" is not recommended since you'll wipe out your ARGV and ENV
3308 The use of reset on dbm associative arrays does not change the dbm file.
3309 (It does, however, flush any entries cached by perl, which may be useful if
3310 you are sharing the dbm file.
3311 Then again, maybe not.)
3312 .Ip "return LIST" 8 3
3313 Returns from a subroutine with the value specified.
3314 (Note that a subroutine can automatically return
3315 the value of the last expression evaluated.
3316 That's the preferred method\*(--use of an explicit
3319 .Ip "reverse(LIST)" 8 4
3320 .Ip "reverse LIST" 8
3321 In an array context, returns an array value consisting of the elements
3322 of LIST in the opposite order.
3323 In a scalar context, returns a string value consisting of the bytes of
3324 the first element of LIST in the opposite order.
3325 .Ip "rewinddir(DIRHANDLE)" 8 5
3326 .Ip "rewinddir DIRHANDLE" 8
3327 Sets the current position to the beginning of the directory for the readdir() routine on DIRHANDLE.
3328 .Ip "rindex(STR,SUBSTR,POSITION)" 8 6
3329 .Ip "rindex(STR,SUBSTR)" 8 4
3330 Works just like index except that it
3331 returns the position of the LAST occurrence of SUBSTR in STR.
3332 If POSITION is specified, returns the last occurrence at or before that
3334 .Ip "rmdir(FILENAME)" 8 4
3335 .Ip "rmdir FILENAME" 8
3336 Deletes the directory specified by FILENAME if it is empty.
3337 If it succeeds it returns 1, otherwise it returns 0 and sets $! (errno).
3338 If FILENAME is omitted, uses $_.
3339 .Ip "s/PATTERN/REPLACEMENT/gieo" 8 3
3340 Searches a string for a pattern, and if found, replaces that pattern with the
3341 replacement text and returns the number of substitutions made.
3342 Otherwise it returns false (0).
3343 The \*(L"g\*(R" is optional, and if present, indicates that all occurrences
3344 of the pattern are to be replaced.
3345 The \*(L"i\*(R" is also optional, and if present, indicates that matching
3346 is to be done in a case-insensitive manner.
3347 The \*(L"e\*(R" is likewise optional, and if present, indicates that
3348 the replacement string is to be evaluated as an expression rather than just
3349 as a double-quoted string.
3350 Any non-alphanumeric delimiter may replace the slashes;
3351 if single quotes are used, no
3352 interpretation is done on the replacement string (the e modifier overrides
3353 this, however); if backquotes are used, the replacement string is a command
3354 to execute whose output will be used as the actual replacement text.
3355 If no string is specified via the =~ or !~ operator,
3356 the $_ string is searched and modified.
3357 (The string specified with =~ must be a scalar variable, an array element,
3358 or an assignment to one of those, i.e. an lvalue.)
3359 If the pattern contains a $ that looks like a variable rather than an
3360 end-of-string test, the variable will be interpolated into the pattern at
3362 If you only want the pattern compiled once the first time the variable is
3363 interpolated, add an \*(L"o\*(R" at the end.
3364 If the PATTERN evaluates to a null string, the most recent successful
3365 regular expression is used instead.
3366 See also the section on regular expressions.
3370 s/\|\e\|bgreen\e\|b/mauve/g; # don't change wintergreen
3372 $path \|=~ \|s|\|/usr/bin|\|/usr/local/bin|;
3374 s/Login: $foo/Login: $bar/; # run-time pattern
3376 ($foo = $bar) =~ s/bar/foo/;
3379 s/\ed+/$&*2/e; # yields \*(L'abc246xyz\*(R'
3380 s/\ed+/sprintf("%5d",$&)/e; # yields \*(L'abc 246xyz\*(R'
3381 s/\ew/$& x 2/eg; # yields \*(L'aabbcc 224466xxyyzz\*(R'
3383 s/\|([^ \|]*\|) *\|([^ \|]*\|)\|/\|$2 $1/; # reverse 1st two fields
3386 (Note the use of $ instead of \|\e\| in the last example. See section
3387 on regular expressions.)
3388 .Ip "scalar(EXPR)" 8 3
3389 Forces EXPR to be interpreted in a scalar context and returns the value
3391 .Ip "seek(FILEHANDLE,POSITION,WHENCE)" 8 3
3392 Randomly positions the file pointer for FILEHANDLE, just like the fseek()
3394 FILEHANDLE may be an expression whose value gives the name of the filehandle.
3395 Returns 1 upon success, 0 otherwise.
3396 .Ip "seekdir(DIRHANDLE,POS)" 8 3
3397 Sets the current position for the readdir() routine on DIRHANDLE.
3398 POS must be a value returned by telldir().
3399 Has the same caveats about possible directory compaction as the corresponding
3400 system library routine.
3401 .Ip "select(FILEHANDLE)" 8 3
3403 Returns the currently selected filehandle.
3404 Sets the current default filehandle for output, if FILEHANDLE is supplied.
3405 This has two effects: first, a
3409 without a filehandle will default to this FILEHANDLE.
3410 Second, references to variables related to output will refer to this output
3412 For example, if you have to set the top of form format for more than
3413 one output channel, you might do the following:
3418 $^ = \'report1_top\';
3420 $^ = \'report2_top\';
3423 FILEHANDLE may be an expression whose value gives the name of the actual filehandle.
3427 $oldfh = select(STDERR); $| = 1; select($oldfh);
3430 .Ip "select(RBITS,WBITS,EBITS,TIMEOUT)" 8 3
3431 This calls the select system call with the bitmasks specified, which can
3432 be constructed using fileno() and vec(), along these lines:
3435 $rin = $win = $ein = '';
3436 vec($rin,fileno(STDIN),1) = 1;
3437 vec($win,fileno(STDOUT),1) = 1;
3441 If you want to select on many filehandles you might wish to write a subroutine:
3445 local(@fhlist) = split(' ',$_[0]);
3448 vec($bits,fileno($_),1) = 1;
3452 $rin = &fhbits('STDIN TTY SOCK');
3458 ($nfound,$timeleft) =
3459 select($rout=$rin, $wout=$win, $eout=$ein, $timeout);
3461 or to block until something becomes ready:
3464 $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);
3467 $nfound = select($rout=$rin, $wout=$win,
3472 Any of the bitmasks can also be undef.
3473 The timeout, if specified, is in seconds, which may be fractional.
3474 NOTE: not all implementations are capable of returning the $timeleft.
3475 If not, they always return $timeleft equal to the supplied $timeout.
3476 .Ip "semctl(ID,SEMNUM,CMD,ARG)" 8 4
3477 Calls the System V IPC function semctl. If CMD is &IPC_STAT or
3478 &GETALL, then ARG must be a variable which will hold the returned
3479 semid_ds structure or semaphore value array. Returns like ioctl: the
3480 undefined value for error, "0 but true" for zero, or the actual return
3482 .Ip "semget(KEY,NSEMS,SIZE,FLAGS)" 8 4
3483 Calls the System V IPC function semget. Returns the semaphore id, or
3484 the undefined value if there is an error.
3485 .Ip "semop(KEY,OPSTRING)" 8 4
3486 Calls the System V IPC function semop to perform semaphore operations
3487 such as signaling and waiting. OPSTRING must be a packed array of
3488 semop structures. Each semop structure can be generated with
3489 \&'pack("sss", $semnum, $semop, $semflag)'. The number of semaphore
3490 operations is implied by the length of OPSTRING. Returns true if
3491 successful, or false if there is an error. As an example, the
3492 following code waits on semaphore $semnum of semaphore id $semid:
3495 $semop = pack("sss", $semnum, -1, 0);
3496 die "Semaphore trouble: $!\en" unless semop($semid, $semop);
3499 To signal the semaphore, replace "-1" with "1".
3500 .Ip "send(SOCKET,MSG,FLAGS,TO)" 8 4
3501 .Ip "send(SOCKET,MSG,FLAGS)" 8
3502 Sends a message on a socket.
3503 Takes the same flags as the system call of the same name.
3504 On unconnected sockets you must specify a destination to send TO.
3505 Returns the number of characters sent, or the undefined value if
3507 .Ip "setpgrp(PID,PGRP)" 8 4
3508 Sets the current process group for the specified PID, 0 for the current
3510 Will produce a fatal error if used on a machine that doesn't implement
3512 .Ip "setpriority(WHICH,WHO,PRIORITY)" 8 4
3513 Sets the current priority for a process, a process group, or a user.
3514 (See setpriority(2).)
3515 Will produce a fatal error if used on a machine that doesn't implement
3517 .Ip "setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)" 8 3
3518 Sets the socket option requested.
3519 Returns undefined if there is an error.
3520 OPTVAL may be specified as undef if you don't want to pass an argument.
3521 .Ip "shift(ARRAY)" 8 6
3524 Shifts the first value of the array off and returns it,
3525 shortening the array by 1 and moving everything down.
3526 If there are no elements in the array, returns the undefined value.
3527 If ARRAY is omitted, shifts the @ARGV array in the main program, and the @_
3528 array in subroutines.
3529 (This is determined lexically.)
3530 See also unshift(), push() and pop().
3531 Shift() and unshift() do the same thing to the left end of an array that push()
3532 and pop() do to the right end.
3533 .Ip "shmctl(ID,CMD,ARG)" 8 4
3534 Calls the System V IPC function shmctl. If CMD is &IPC_STAT, then ARG
3535 must be a variable which will hold the returned shmid_ds structure.
3536 Returns like ioctl: the undefined value for error, "0 but true" for
3537 zero, or the actual return value otherwise.
3538 .Ip "shmget(KEY,SIZE,FLAGS)" 8 4
3539 Calls the System V IPC function shmget. Returns the shared memory
3540 segment id, or the undefined value if there is an error.
3541 .Ip "shmread(ID,VAR,POS,SIZE)" 8 4
3542 .Ip "shmwrite(ID,STRING,POS,SIZE)" 8
3543 Reads or writes the System V shared memory segment ID starting at
3544 position POS for size SIZE by attaching to it, copying in/out, and
3545 detaching from it. When reading, VAR must be a variable which
3546 will hold the data read. When writing, if STRING is too long,
3547 only SIZE bytes are used; if STRING is too short, nulls are
3548 written to fill out SIZE bytes. Return true if successful, or
3549 false if there is an error.
3550 .Ip "shutdown(SOCKET,HOW)" 8 3
3551 Shuts down a socket connection in the manner indicated by HOW, which has
3552 the same interpretation as in the system call of the same name.
3555 Returns the sine of EXPR (expressed in radians).
3556 If EXPR is omitted, returns sine of $_.
3557 .Ip "sleep(EXPR)" 8 6
3560 Causes the script to sleep for EXPR seconds, or forever if no EXPR.
3561 May be interrupted by sending the process a SIGALARM.
3562 Returns the number of seconds actually slept.
3563 .Ip "socket(SOCKET,DOMAIN,TYPE,PROTOCOL)" 8 3
3564 Opens a socket of the specified kind and attaches it to filehandle SOCKET.
3565 DOMAIN, TYPE and PROTOCOL are specified the same as for the system call
3567 You may need to run h2ph on sys/socket.h to get the proper values handy
3568 in a perl library file.
3569 Return true if successful.
3570 See the example in the section on Interprocess Communication.
3571 .Ip "socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)" 8 3
3572 Creates an unnamed pair of sockets in the specified domain, of the specified
3574 DOMAIN, TYPE and PROTOCOL are specified the same as for the system call
3576 If unimplemented, yields a fatal error.
3577 Return true if successful.
3578 .Ip "sort(SUBROUTINE LIST)" 8 9
3580 .Ip "sort SUBROUTINE LIST" 8
3582 Sorts the LIST and returns the sorted array value.
3583 Nonexistent values of arrays are stripped out.
3584 If SUBROUTINE is omitted, sorts in standard string comparison order.
3585 If SUBROUTINE is specified, gives the name of a subroutine that returns
3586 an integer less than, equal to, or greater than 0,
3587 depending on how the elements of the array are to be ordered.
3588 (The <=> and cmp operators are extremely useful in such routines.)
3589 In the interests of efficiency the normal calling code for subroutines
3590 is bypassed, with the following effects: the subroutine may not be a recursive
3591 subroutine, and the two elements to be compared are passed into the subroutine
3592 not via @_ but as $a and $b (see example below).
3593 They are passed by reference so don't modify $a and $b.
3594 SUBROUTINE may be a scalar variable name, in which case the value provides
3595 the name of the subroutine to use.
3601 $age{$a} <=> $age{$b}; # presuming integers
3603 @sortedclass = sort byage @class;
3606 sub reverse { $b cmp $a; }
3607 @harry = (\'dog\',\'cat\',\'x\',\'Cain\',\'Abel\');
3608 @george = (\'gone\',\'chased\',\'yz\',\'Punished\',\'Axed\');
3610 # prints AbelCaincatdogx
3611 print sort reverse @harry;
3612 # prints xdogcatCainAbel
3613 print sort @george, \'to\', @harry;
3614 # prints AbelAxedCainPunishedcatchaseddoggonetoxyz
3617 .Ip "splice(ARRAY,OFFSET,LENGTH,LIST)" 8 8
3618 .Ip "splice(ARRAY,OFFSET,LENGTH)" 8
3619 .Ip "splice(ARRAY,OFFSET)" 8
3620 Removes the elements designated by OFFSET and LENGTH from an array, and
3621 replaces them with the elements of LIST, if any.
3622 Returns the elements removed from the array.
3623 The array grows or shrinks as necessary.
3624 If LENGTH is omitted, removes everything from OFFSET onward.
3625 The following equivalencies hold (assuming $[ == 0):
3628 push(@a,$x,$y)\h'|3.5i'splice(@a,$#a+1,0,$x,$y)
3629 pop(@a)\h'|3.5i'splice(@a,-1)
3630 shift(@a)\h'|3.5i'splice(@a,0,1)
3631 unshift(@a,$x,$y)\h'|3.5i'splice(@a,0,0,$x,$y)
3632 $a[$x] = $y\h'|3.5i'splice(@a,$x,1,$y);
3634 Example, assuming array lengths are passed before arrays:
3636 sub aeq { # compare two array values
3637 local(@a) = splice(@_,0,shift);
3638 local(@b) = splice(@_,0,shift);
3639 return 0 unless @a == @b; # same len?
3641 return 0 if pop(@a) ne pop(@b);
3645 if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }
3648 .Ip "split(/PATTERN/,EXPR,LIMIT)" 8 8
3649 .Ip "split(/PATTERN/,EXPR)" 8 8
3650 .Ip "split(/PATTERN/)" 8
3652 Splits a string into an array of strings, and returns it.
3653 (If not in an array context, returns the number of fields found and splits
3655 (In an array context, you can force the split into @_
3656 by using ?? as the pattern delimiters, but it still returns the array value.))
3657 If EXPR is omitted, splits the $_ string.
3658 If PATTERN is also omitted, splits on whitespace (/[\ \et\en]+/).
3659 Anything matching PATTERN is taken to be a delimiter separating the fields.
3660 (Note that the delimiter may be longer than one character.)
3661 If LIMIT is specified, splits into no more than that many fields (though it
3662 may split into fewer).
3663 If LIMIT is unspecified, trailing null fields are stripped (which
3664 potential users of pop() would do well to remember).
3665 A pattern matching the null string (not to be confused with a null pattern //,
3666 which is just one member of the set of patterns matching a null string)
3667 will split the value of EXPR into separate characters at each point it
3672 print join(\':\', split(/ */, \'hi there\'));
3675 produces the output \*(L'h:i:t:h:e:r:e\*(R'.
3677 The LIMIT parameter can be used to partially split a line
3680 ($login, $passwd, $remainder) = split(\|/\|:\|/\|, $_, 3);
3683 (When assigning to a list, if LIMIT is omitted, perl supplies a LIMIT one
3684 larger than the number of variables in the list, to avoid unnecessary work.
3685 For the list above LIMIT would have been 4 by default.
3686 In time critical applications it behooves you not to split into
3687 more fields than you really need.)
3689 If the PATTERN contains parentheses, additional array elements are created
3690 from each matching substring in the delimiter.
3692 split(/([,-])/,"1-10,20");
3694 produces the array value
3698 The pattern /PATTERN/ may be replaced with an expression to specify patterns
3699 that vary at runtime.
3700 (To do runtime compilation only once, use /$variable/o.)
3701 As a special case, specifying a space (\'\ \') will split on white space
3702 just as split with no arguments does, but leading white space does NOT
3703 produce a null first field.
3704 Thus, split(\'\ \') can be used to emulate
3706 default behavior, whereas
3707 split(/\ /) will give you as many null initial fields as there are
3714 open(passwd, \'/etc/passwd\');
3717 ($login, $passwd, $uid, $gid, $gcos, $home, $shell) = split(\|/\|:\|/\|);
3720 ($login, $passwd, $uid, $gid, $gcos, $home, $shell)
3721 = split(\|/\|:\|/\|);
3727 (Note that $shell above will still have a newline on it. See chop().)
3730 .Ip "sprintf(FORMAT,LIST)" 8 4
3731 Returns a string formatted by the usual printf conventions.
3732 The * character is not supported.
3733 .Ip "sqrt(EXPR)" 8 4
3735 Return the square root of EXPR.
3736 If EXPR is omitted, returns square root of $_.
3737 .Ip "srand(EXPR)" 8 4
3739 Sets the random number seed for the
3742 If EXPR is omitted, does srand(time).
3743 .Ip "stat(FILEHANDLE)" 8 8
3744 .Ip "stat FILEHANDLE" 8
3746 .Ip "stat SCALARVARIABLE" 8
3747 Returns a 13-element array giving the statistics for a file, either the file
3748 opened via FILEHANDLE, or named by EXPR.
3749 Typically used as follows:
3753 ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
3754 $atime,$mtime,$ctime,$blksize,$blocks)
3758 If stat is passed the special filehandle consisting of an underline,
3759 no stat is done, but the current contents of the stat structure from
3760 the last stat or filetest are returned.
3765 if (-x $file && (($d) = stat(_)) && $d < 0) {
3766 print "$file is executable NFS file\en";
3770 (This only works on machines for which the device number is negative under NFS.)
3771 .Ip "study(SCALAR)" 8 6
3772 .Ip "study SCALAR" 8
3774 Takes extra time to study SCALAR ($_ if unspecified) in anticipation of
3775 doing many pattern matches on the string before it is next modified.
3776 This may or may not save time, depending on the nature and number of patterns
3777 you are searching on, and on the distribution of character frequencies in
3778 the string to be searched\*(--you probably want to compare runtimes with and
3779 without it to see which runs faster.
3780 Those loops which scan for many short constant strings (including the constant
3781 parts of more complex patterns) will benefit most.
3782 You may have only one study active at a time\*(--if you study a different
3783 scalar the first is \*(L"unstudied\*(R".
3784 (The way study works is this: a linked list of every character in the string
3785 to be searched is made, so we know, for example, where all the \*(L'k\*(R' characters
3787 From each search string, the rarest character is selected, based on some
3788 static frequency tables constructed from some C programs and English text.
3789 Only those places that contain this \*(L"rarest\*(R" character are examined.)
3791 For example, here is a loop which inserts index producing entries before any line
3792 containing a certain pattern:
3798 print ".IX foo\en" if /\ebfoo\eb/;
3799 print ".IX bar\en" if /\ebbar\eb/;
3800 print ".IX blurfl\en" if /\ebblurfl\eb/;
3806 In searching for /\ebfoo\eb/, only those locations in $_ that contain \*(L'f\*(R'
3807 will be looked at, because \*(L'f\*(R' is rarer than \*(L'o\*(R'.
3808 In general, this is a big win except in pathological cases.
3809 The only question is whether it saves you more time than it took to build
3810 the linked list in the first place.
3812 Note that if you have to look for strings that you don't know till runtime,
3813 you can build an entire loop as a string and eval that to avoid recompiling
3814 all your patterns all the time.
3815 Together with undefining $/ to input entire files as one record, this can
3816 be very fast, often faster than specialized programs like fgrep.
3817 The following scans a list of files (@files)
3818 for a list of words (@words), and prints out the names of those files that
3823 $search = \'while (<>) { study;\';
3824 foreach $word (@words) {
3825 $search .= "++\e$seen{\e$ARGV} if /\eb$word\eb/;\en";
3830 eval $search; # this screams
3831 $/ = "\en"; # put back to normal input delim
3832 foreach $file (sort keys(%seen)) {
3837 .Ip "substr(EXPR,OFFSET,LEN)" 8 2
3838 .Ip "substr(EXPR,OFFSET)" 8 2
3839 Extracts a substring out of EXPR and returns it.
3840 First character is at offset 0, or whatever you've set $[ to.
3841 If OFFSET is negative, starts that far from the end of the string.
3842 If LEN is omitted, returns everything to the end of the string.
3843 You can use the substr() function as an lvalue, in which case EXPR must
3845 If you assign something shorter than LEN, the string will shrink, and
3846 if you assign something longer than LEN, the string will grow to accommodate it.
3847 To keep the string the same length you may need to pad or chop your value using
3849 .Ip "symlink(OLDFILE,NEWFILE)" 8 2
3850 Creates a new filename symbolically linked to the old filename.
3851 Returns 1 for success, 0 otherwise.
3852 On systems that don't support symbolic links, produces a fatal error at
3854 To check for that, use eval:
3857 $symlink_exists = (eval \'symlink("","");\', $@ eq \'\');
3860 .Ip "syscall(LIST)" 8 6
3861 .Ip "syscall LIST" 8
3862 Calls the system call specified as the first element of the list, passing
3863 the remaining elements as arguments to the system call.
3864 If unimplemented, produces a fatal error.
3865 The arguments are interpreted as follows: if a given argument is numeric,
3866 the argument is passed as an int.
3867 If not, the pointer to the string value is passed.
3868 You are responsible to make sure a string is pre-extended long enough
3869 to receive any result that might be written into a string.
3870 If your integer arguments are not literals and have never been interpreted
3871 in a numeric context, you may need to add 0 to them to force them to look
3875 require 'syscall.ph'; # may need to run h2ph
3876 syscall(&SYS_write, fileno(STDOUT), "hi there\en", 9);
3879 .Ip "sysread(FILEHANDLE,SCALAR,LENGTH,OFFSET)" 8 5
3880 .Ip "sysread(FILEHANDLE,SCALAR,LENGTH)" 8 5
3881 Attempts to read LENGTH bytes of data into variable SCALAR from the specified
3882 FILEHANDLE, using the system call read(2).
3883 It bypasses stdio, so mixing this with other kinds of reads may cause
3885 Returns the number of bytes actually read, or undef if there was an error.
3886 SCALAR will be grown or shrunk to the length actually read.
3887 An OFFSET may be specified to place the read data at some other place
3888 than the beginning of the string.
3889 .Ip "system(LIST)" 8 6
3891 Does exactly the same thing as \*(L"exec LIST\*(R" except that a fork
3892 is done first, and the parent process waits for the child process to complete.
3893 Note that argument processing varies depending on the number of arguments.
3894 The return value is the exit status of the program as returned by the wait()
3896 To get the actual exit value divide by 256.
3899 .Ip "syswrite(FILEHANDLE,SCALAR,LENGTH,OFFSET)" 8 5
3900 .Ip "syswrite(FILEHANDLE,SCALAR,LENGTH)" 8 5
3901 Attempts to write LENGTH bytes of data from variable SCALAR to the specified
3902 FILEHANDLE, using the system call write(2).
3903 It bypasses stdio, so mixing this with prints may cause
3905 Returns the number of bytes actually written, or undef if there was an error.
3906 An OFFSET may be specified to place the read data at some other place
3907 than the beginning of the string.
3908 .Ip "tell(FILEHANDLE)" 8 6
3909 .Ip "tell FILEHANDLE" 8 6
3911 Returns the current file position for FILEHANDLE.
3912 FILEHANDLE may be an expression whose value gives the name of the actual
3914 If FILEHANDLE is omitted, assumes the file last read.
3915 .Ip "telldir(DIRHANDLE)" 8 5
3916 .Ip "telldir DIRHANDLE" 8
3917 Returns the current position of the readdir() routines on DIRHANDLE.
3918 Value may be given to seekdir() to access a particular location in
3920 Has the same caveats about possible directory compaction as the corresponding
3921 system library routine.
3923 Returns the number of non-leap seconds since 00:00:00 UTC, January 1, 1970.
3924 Suitable for feeding to gmtime() and localtime().
3926 Returns a four-element array giving the user and system times, in seconds, for this
3927 process and the children of this process.
3929 ($user,$system,$cuser,$csystem) = times;
3931 .Ip "tr/SEARCHLIST/REPLACEMENTLIST/cds" 8 5
3932 .Ip "y/SEARCHLIST/REPLACEMENTLIST/cds" 8
3933 Translates all occurrences of the characters found in the search list with
3934 the corresponding character in the replacement list.
3935 It returns the number of characters replaced or deleted.
3936 If no string is specified via the =~ or !~ operator,
3937 the $_ string is translated.
3938 (The string specified with =~ must be a scalar variable, an array element,
3939 or an assignment to one of those, i.e. an lvalue.)
3944 is provided as a synonym for
3947 If the c modifier is specified, the SEARCHLIST character set is complemented.
3948 If the d modifier is specified, any characters specified by SEARCHLIST that
3949 are not found in REPLACEMENTLIST are deleted.
3950 (Note that this is slightly more flexible than the behavior of some
3952 programs, which delete anything they find in the SEARCHLIST, period.)
3953 If the s modifier is specified, sequences of characters that were translated
3954 to the same character are squashed down to 1 instance of the character.
3956 If the d modifier was used, the REPLACEMENTLIST is always interpreted exactly
3958 Otherwise, if the REPLACEMENTLIST is shorter than the SEARCHLIST,
3959 the final character is replicated till it is long enough.
3960 If the REPLACEMENTLIST is null, the SEARCHLIST is replicated.
3961 This latter is useful for counting characters in a class, or for squashing
3962 character sequences in a class.
3967 $ARGV[1] \|=~ \|y/A\-Z/a\-z/; \h'|3i'# canonicalize to lower case
3969 $cnt = tr/*/*/; \h'|3i'# count the stars in $_
3971 $cnt = tr/0\-9//; \h'|3i'# count the digits in $_
3973 tr/a\-zA\-Z//s; \h'|3i'# bookkeeper \-> bokeper
3975 ($HOST = $host) =~ tr/a\-z/A\-Z/;
3977 y/a\-zA\-Z/ /cs; \h'|3i'# change non-alphas to single space
3979 tr/\e200\-\e377/\e0\-\e177/;\h'|3i'# delete 8th bit
3982 .Ip "truncate(FILEHANDLE,LENGTH)" 8 4
3983 .Ip "truncate(EXPR,LENGTH)" 8
3984 Truncates the file opened on FILEHANDLE, or named by EXPR, to the specified
3986 Produces a fatal error if truncate isn't implemented on your system.
3987 .Ip "umask(EXPR)" 8 4
3990 Sets the umask for the process and returns the old one.
3991 If EXPR is omitted, merely returns current umask.
3992 .Ip "undef(EXPR)" 8 6
3995 Undefines the value of EXPR, which must be an lvalue.
3996 Use only on a scalar value, an entire array, or a subroutine name (using &).
3997 (Undef will probably not do what you expect on most predefined variables or
3999 Always returns the undefined value.
4000 You can omit the EXPR, in which case nothing is undefined, but you still
4001 get an undefined value that you could, for instance, return from a subroutine.
4007 undef $bar{'blurfl'};
4011 return (wantarray ? () : undef) if $they_blew_it;
4014 .Ip "unlink(LIST)" 8 4
4016 Deletes a list of files.
4017 Returns the number of files successfully deleted.
4021 $cnt = unlink \'a\', \'b\', \'c\';
4026 Note: unlink will not delete directories unless you are superuser and the
4030 Even if these conditions are met, be warned that unlinking a directory
4031 can inflict damage on your filesystem.
4033 .Ip "unpack(TEMPLATE,EXPR)" 8 4
4034 Unpack does the reverse of pack: it takes a string representing
4035 a structure and expands it out into an array value, returning the array
4037 (In a scalar context, it merely returns the first value produced.)
4038 The TEMPLATE has the same format as in the pack function.
4039 Here's a subroutine that does substring:
4044 local($what,$where,$howmuch) = @_;
4045 unpack("x$where a$howmuch", $what);
4051 sub ord { unpack("c",$_[0]); }
4054 In addition, you may prefix a field with a %<number> to indicate that
4055 you want a <number>-bit checksum of the items instead of the items themselves.
4056 Default is a 16-bit checksum.
4057 For example, the following computes the same number as the System V sum program:
4062 $checksum += unpack("%16C*", $_);
4067 .Ip "unshift(ARRAY,LIST)" 8 4
4068 Does the opposite of a
4070 Or the opposite of a
4072 depending on how you look at it.
4073 Prepends list to the front of the array, and returns the number of elements
4077 unshift(ARGV, \'\-e\') unless $ARGV[0] =~ /^\-/;
4080 .Ip "utime(LIST)" 8 2
4081 .Ip "utime LIST" 8 2
4082 Changes the access and modification times on each file of a list of files.
4083 The first two elements of the list must be the NUMERICAL access and
4084 modification times, in that order.
4085 Returns the number of files successfully changed.
4086 The inode modification time of each file is set to the current time.
4087 Example of a \*(L"touch\*(R" command:
4093 utime $now, $now, @ARGV;
4096 .Ip "values(ASSOC_ARRAY)" 8 6
4097 .Ip "values ASSOC_ARRAY" 8
4098 Returns a normal array consisting of all the values of the named associative
4100 The values are returned in an apparently random order, but it is the same order
4101 as either the keys() or each() function would produce on the same array.
4102 See also keys() and each().
4103 .Ip "vec(EXPR,OFFSET,BITS)" 8 2
4104 Treats a string as a vector of unsigned integers, and returns the value
4105 of the bitfield specified.
4106 May also be assigned to.
4107 BITS must be a power of two from 1 to 32.
4109 Vectors created with vec() can also be manipulated with the logical operators
4111 which will assume a bit vector operation is desired when both operands are
4113 This interpretation is not enabled unless there is at least one vec() in
4114 your program, to protect older programs.
4116 To transform a bit vector into a string or array of 0's and 1's, use these:
4119 $bits = unpack("b*", $vector);
4120 @bits = split(//, unpack("b*", $vector));
4123 If you know the exact length in bits, it can be used in place of the *.
4125 Waits for a child process to terminate and returns the pid of the deceased
4126 process, or -1 if there are no child processes.
4127 The status is returned in $?.
4128 .Ip "waitpid(PID,FLAGS)" 8 6
4129 Waits for a particular child process to terminate and returns the pid of the deceased
4130 process, or -1 if there is no such child process.
4131 The status is returned in $?.
4135 require "sys/wait.h";
4137 waitpid(-1,&WNOHANG);
4140 then you can do a non-blocking wait for any process. Non-blocking wait
4141 is only available on machines supporting either the
4146 However, waiting for a particular pid with FLAGS of 0 is implemented
4147 everywhere. (Perl emulates the system call by remembering the status
4148 values of processes that have exited but have not been harvested by the
4151 Returns true if the context of the currently executing subroutine
4152 is looking for an array value.
4153 Returns false if the context is looking for a scalar.
4156 return wantarray ? () : undef;
4159 .Ip "warn(LIST)" 8 4
4161 Produces a message on STDERR just like \*(L"die\*(R", but doesn't exit.
4162 .Ip "write(FILEHANDLE)" 8 6
4165 Writes a formatted record (possibly multi-line) to the specified file,
4166 using the format associated with that file.
4167 By default the format for a file is the one having the same name is the
4168 filehandle, but the format for the current output channel (see
4170 may be set explicitly
4171 by assigning the name of the format to the $~ variable.
4173 Top of form processing is handled automatically:
4174 if there is insufficient room on the current page for the formatted
4175 record, the page is advanced by writing a form feed,
4176 a special top-of-page format is used
4177 to format the new page header, and then the record is written.
4178 By default the top-of-page format is \*(L"top\*(R", but it
4180 format of your choice by assigning the name to the $^ variable.
4181 The number of lines remaining on the current page is in variable $-, which
4182 can be set to 0 to force a new page.
4184 If FILEHANDLE is unspecified, output goes to the current default output channel,
4187 but may be changed by the
4190 If the FILEHANDLE is an EXPR, then the expression is evaluated and the
4191 resulting string is used to look up the name of the FILEHANDLE at run time.
4192 For more on formats, see the section on formats later on.
4194 Note that write is NOT the opposite of read.
4197 operators have the following associativity and precedence:
4200 nonassoc\h'|1i'print printf exec system sort reverse
4201 \h'1.5i'chmod chown kill unlink utime die return
4203 right\h'|1i'= += \-= *= etc.
4210 nonassoc\h'|1i'== != <=> eq ne cmp
4211 nonassoc\h'|1i'< > <= >= lt gt le ge
4212 nonassoc\h'|1i'chdir exit eval reset sleep rand umask
4213 nonassoc\h'|1i'\-r \-w \-x etc.
4218 right\h'|1i'! ~ and unary minus
4220 nonassoc\h'|1i'++ \-\|\-
4221 left\h'|1i'\*(L'(\*(R'
4224 As mentioned earlier, if any list operator (print, etc.) or
4225 any unary operator (chdir, etc.)
4226 is followed by a left parenthesis as the next token on the same line,
4227 the operator and arguments within parentheses are taken to
4228 be of highest precedence, just like a normal function call.
4232 chdir $foo || die;\h'|3i'# (chdir $foo) || die
4233 chdir($foo) || die;\h'|3i'# (chdir $foo) || die
4234 chdir ($foo) || die;\h'|3i'# (chdir $foo) || die
4235 chdir +($foo) || die;\h'|3i'# (chdir $foo) || die
4237 but, because * is higher precedence than ||:
4239 chdir $foo * 20;\h'|3i'# chdir ($foo * 20)
4240 chdir($foo) * 20;\h'|3i'# (chdir $foo) * 20
4241 chdir ($foo) * 20;\h'|3i'# (chdir $foo) * 20
4242 chdir +($foo) * 20;\h'|3i'# chdir ($foo * 20)
4244 rand 10 * 20;\h'|3i'# rand (10 * 20)
4245 rand(10) * 20;\h'|3i'# (rand 10) * 20
4246 rand (10) * 20;\h'|3i'# (rand 10) * 20
4247 rand +(10) * 20;\h'|3i'# rand (10 * 20)
4250 In the absence of parentheses,
4251 the precedence of list operators such as print, sort or chmod is
4252 either very high or very low depending on whether you look at the left
4253 side of operator or the right side of it.
4257 @ary = (1, 3, sort 4, 2);
4258 print @ary; # prints 1324
4261 the commas on the right of the sort are evaluated before the sort, but
4262 the commas on the left are evaluated after.
4263 In other words, list operators tend to gobble up all the arguments that
4264 follow them, and then act like a simple term with regard to the preceding
4266 Note that you have to be careful with parens:
4270 # These evaluate exit before doing the print:
4271 print($foo, exit); # Obviously not what you want.
4272 print $foo, exit; # Nor is this.
4275 # These do the print before evaluating exit:
4276 (print $foo), exit; # This is what you want.
4277 print($foo), exit; # Or this.
4278 print ($foo), exit; # Or even this.
4282 print ($foo & 255) + 1, "\en";
4285 probably doesn't do what you expect at first glance.
4287 A subroutine may be declared as follows:
4294 Any arguments passed to the routine come in as array @_,
4295 that is ($_[0], $_[1], .\|.\|.).
4296 The array @_ is a local array, but its values are references to the
4297 actual scalar parameters.
4298 The return value of the subroutine is the value of the last expression
4299 evaluated, and can be either an array value or a scalar value.
4300 Alternately, a return statement may be used to specify the returned value and
4301 exit the subroutine.
4302 To create local variables see the
4306 A subroutine is called using the
4308 operator or the & operator.
4315 local($max) = pop(@_);
4317 $max = $foo \|if \|$max < $foo;
4323 $bestday = &MAX($mon,$tue,$wed,$thu,$fri);
4328 # get a line, combining continuation lines
4329 # that start with whitespace
4331 $thisline = $lookahead;
4332 line: while ($lookahead = <STDIN>) {
4333 if ($lookahead \|=~ \|/\|^[ \^\e\|t]\|/\|) {
4334 $thisline \|.= \|$lookahead;
4343 $lookahead = <STDIN>; # get first line
4344 while ($_ = do get_line(\|)) {
4351 Use array assignment to a local list to name your formal arguments:
4354 local($key, $value) = @_;
4355 $foo{$key} = $value unless $foo{$key};
4359 This also has the effect of turning call-by-reference into call-by-value,
4360 since the assignment copies the values.
4362 Subroutines may be called recursively.
4363 If a subroutine is called using the & form, the argument list is optional.
4364 If omitted, no @_ array is set up for the subroutine; the @_ array at the
4365 time of the call is visible to subroutine instead.
4368 do foo(1,2,3); # pass three arguments
4369 &foo(1,2,3); # the same
4371 do foo(); # pass a null list
4373 &foo; # pass no arguments\*(--more efficient
4376 .Sh "Passing By Reference"
4377 Sometimes you don't want to pass the value of an array to a subroutine but
4378 rather the name of it, so that the subroutine can modify the global copy
4379 of it rather than working with a local copy.
4380 In perl you can refer to all the objects of a particular name by prefixing
4381 the name with a star: *foo.
4382 When evaluated, it produces a scalar value that represents all the objects
4383 of that name, including any filehandle, format or subroutine.
4384 When assigned to within a local() operation, it causes the name mentioned
4385 to refer to whatever * value was assigned to it.
4390 local(*someary) = @_;
4391 foreach $elem (@someary) {
4399 Assignment to *name is currently recommended only inside a local().
4400 You can actually assign to *name anywhere, but the previous referent of
4401 *name may be stranded forever.
4402 This may or may not bother you.
4404 Note that scalars are already passed by reference, so you can modify scalar
4405 arguments without using this mechanism by referring explicitly to the $_[nnn]
4407 You can modify all the elements of an array by passing all the elements
4408 as scalars, but you have to use the * mechanism to push, pop or change the
4410 The * mechanism will probably be more efficient in any case.
4412 Since a *name value contains unprintable binary data, if it is used as
4413 an argument in a print, or as a %s argument in a printf or sprintf, it
4414 then has the value '*name', just so it prints out pretty.
4416 Even if you don't want to modify an array, this mechanism is useful for
4417 passing multiple arrays in a single LIST, since normally the LIST mechanism
4418 will merge all the array values so that you can't extract out the
4420 .Sh "Regular Expressions"
4421 The patterns used in pattern matching are regular expressions such as
4422 those supplied in the Version 8 regexp routines.
4423 (In fact, the routines are derived from Henry Spencer's freely redistributable
4424 reimplementation of the V8 routines.)
4425 In addition, \ew matches an alphanumeric character (including \*(L"_\*(R") and \eW a nonalphanumeric.
4426 Word boundaries may be matched by \eb, and non-boundaries by \eB.
4427 A whitespace character is matched by \es, non-whitespace by \eS.
4428 A numeric character is matched by \ed, non-numeric by \eD.
4429 You may use \ew, \es and \ed within character classes.
4430 Also, \en, \er, \ef, \et and \eNNN have their normal interpretations.
4431 Within character classes \eb represents backspace rather than a word boundary.
4432 Alternatives may be separated by |.
4433 The bracketing construct \|(\ .\|.\|.\ \|) may also be used, in which case \e<digit>
4434 matches the digit'th substring.
4435 (Outside of the pattern, always use $ instead of \e in front of the digit.
4436 The scope of $<digit> (and $\`, $& and $\')
4437 extends to the end of the enclosing BLOCK or eval string, or to
4438 the next pattern match with subexpressions.
4439 The \e<digit> notation sometimes works outside the current pattern, but should
4440 not be relied upon.)
4441 You may have as many parentheses as you wish. If you have more than 9
4442 substrings, the variables $10, $11, ... refer to the corresponding
4443 substring. Within the pattern, \e10, \e11,
4444 etc. refer back to substrings if there have been at least that many left parens
4445 before the backreference. Otherwise (for backward compatibilty) \e10
4446 is the same as \e010, a backspace,
4447 and \e11 the same as \e011, a tab.
4449 (\e1 through \e9 are always backreferences.)
4451 $+ returns whatever the last bracket match matched.
4452 $& returns the entire matched string.
4453 ($0 used to return the same thing, but not any more.)
4454 $\` returns everything before the matched string.
4455 $\' returns everything after the matched string.
4459 s/\|^\|([^ \|]*\|) \|*([^ \|]*\|)\|/\|$2 $1\|/; # swap first two words
4462 if (/\|Time: \|(.\|.\|):\|(.\|.\|):\|(.\|.\|)\|/\|) {
4469 By default, the ^ character is only guaranteed to match at the beginning
4471 the $ character only at the end (or before the newline at the end)
4474 does certain optimizations with the assumption that the string contains
4476 The behavior of ^ and $ on embedded newlines will be inconsistent.
4477 You may, however, wish to treat a string as a multi-line buffer, such that
4478 the ^ will match after any newline within the string, and $ will match
4480 At the cost of a little more overhead, you can do this by setting the variable
4482 Setting it back to 0 makes
4484 revert to its old behavior.
4486 To facilitate multi-line substitutions, the . character never matches a newline
4487 (even when $* is 0).
4488 In particular, the following leaves a newline on the $_ string:
4492 s/.*(some_string).*/$1/;
4494 If the newline is unwanted, try one of
4496 s/.*(some_string).*\en/$1/;
4497 s/.*(some_string)[^\e000]*/$1/;
4498 s/.*(some_string)(.|\en)*/$1/;
4499 chop; s/.*(some_string).*/$1/;
4500 /(some_string)/ && ($_ = $1);
4503 Any item of a regular expression may be followed with digits in curly brackets
4504 of the form {n,m}, where n gives the minimum number of times to match the item
4505 and m gives the maximum.
4506 The form {n} is equivalent to {n,n} and matches exactly n times.
4507 The form {n,} matches n or more times.
4508 (If a curly bracket occurs in any other context, it is treated as a regular
4510 The * modifier is equivalent to {0,}, the + modifier to {1,} and the ? modifier
4512 There is no limit to the size of n or m, but large numbers will chew up
4515 You will note that all backslashed metacharacters in
4518 such as \eb, \ew, \en.
4519 Unlike some other regular expression languages, there are no backslashed
4520 symbols that aren't alphanumeric.
4521 So anything that looks like \e\e, \e(, \e), \e<, \e>, \e{, or \e} is always
4522 interpreted as a literal character, not a metacharacter.
4523 This makes it simple to quote a string that you want to use for a pattern
4524 but that you are afraid might contain metacharacters.
4525 Simply quote all the non-alphanumeric characters:
4528 $pattern =~ s/(\eW)/\e\e$1/g;
4532 Output record formats for use with the
4534 operator may declared as follows:
4543 If name is omitted, format \*(L"STDOUT\*(R" is defined.
4544 FORMLIST consists of a sequence of lines, each of which may be of one of three
4549 A \*(L"picture\*(R" line giving the format for one output line.
4551 An argument line supplying values to plug into a picture line.
4553 Picture lines are printed exactly as they look, except for certain fields
4554 that substitute values into the line.
4555 Each picture field starts with either @ or ^.
4556 The @ field (not to be confused with the array marker @) is the normal
4557 case; ^ fields are used
4558 to do rudimentary multi-line text block filling.
4559 The length of the field is supplied by padding out the field
4560 with multiple <, >, or | characters to specify, respectively, left justification,
4561 right justification, or centering.
4562 As an alternate form of right justification,
4563 you may also use # characters (with an optional .) to specify a numeric field.
4564 (Use of ^ instead of @ causes the field to be blanked if undefined.)
4565 If any of the values supplied for these fields contains a newline, only
4566 the text up to the newline is printed.
4567 The special field @* can be used for printing multi-line values.
4568 It should appear by itself on a line.
4570 The values are specified on the following line, in the same order as
4572 The values should be separated by commas.
4574 Picture fields that begin with ^ rather than @ are treated specially.
4575 The value supplied must be a scalar variable name which contains a text
4578 puts as much text as it can into the field, and then chops off the front
4579 of the string so that the next time the variable is referenced,
4580 more of the text can be printed.
4581 Normally you would use a sequence of fields in a vertical stack to print
4582 out a block of text.
4583 If you like, you can end the final field with .\|.\|., which will appear in the
4584 output if the text was too long to appear in its entirety.
4585 You can change which characters are legal to break on by changing the
4586 variable $: to a list of the desired characters.
4588 Since use of ^ fields can produce variable length records if the text to be
4589 formatted is short, you can suppress blank lines by putting the tilde (~)
4590 character anywhere in the line.
4591 (Normally you should put it in the front if possible, for visibility.)
4592 The tilde will be translated to a space upon output.
4593 If you put a second tilde contiguous to the first, the line will be repeated
4594 until all the fields on the line are exhausted.
4595 (If you use a field of the @ variety, the expression you supply had better
4596 not give the same value every time forever!)
4605 # a report on the /etc/passwd file
4608 Name Login Office Uid Gid Home
4609 ------------------------------------------------------------------
4612 @<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
4613 $name, $login, $office,$uid,$gid, $home
4617 # a report from a bug report form
4620 @<<<<<<<<<<<<<<<<<<<<<<< @||| @>>>>>>>>>>>>>>>>>>>>>>>
4622 ------------------------------------------------------------------
4625 Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4627 Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4628 \& $index, $description
4629 Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4630 \& $priority, $date, $description
4631 From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4632 \& $from, $description
4633 Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4634 \& $programmer, $description
4635 \&~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4637 \&~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4639 \&~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4641 \&~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
4643 \&~ ^<<<<<<<<<<<<<<<<<<<<<<<...
4651 It is possible to intermix prints with writes on the same output channel,
4652 but you'll have to handle $\- (lines left on the page) yourself.
4654 If you are printing lots of fields that are usually blank, you should consider
4655 using the reset operator between records.
4656 Not only is it more efficient, but it can prevent the bug of adding another
4657 field and forgetting to zero it.
4658 .Sh "Interprocess Communication"
4659 The IPC facilities of perl are built on the Berkeley socket mechanism.
4660 If you don't have sockets, you can ignore this section.
4661 The calls have the same names as the corresponding system calls,
4662 but the arguments tend to differ, for two reasons.
4663 First, perl file handles work differently than C file descriptors.
4664 Second, perl already knows the length of its strings, so you don't need
4665 to pass that information.
4666 Here is a sample client (untested):
4669 ($them,$port) = @ARGV;
4670 $port = 2345 unless $port;
4671 $them = 'localhost' unless $them;
4673 $SIG{'INT'} = 'dokill';
4674 sub dokill { kill 9,$child if $child; }
4676 require 'sys/socket.ph';
4678 $sockaddr = 'S n a4 x8';
4679 chop($hostname = `hostname`);
4681 ($name, $aliases, $proto) = getprotobyname('tcp');
4682 ($name, $aliases, $port) = getservbyname($port, 'tcp')
4683 unless $port =~ /^\ed+$/;
4685 ($name, $aliases, $type, $len, $thisaddr) = gethostbyname($hostname);
4688 ($name, $aliases, $type, $len, $thisaddr) =
4689 gethostbyname($hostname);
4691 ($name, $aliases, $type, $len, $thataddr) = gethostbyname($them);
4693 $this = pack($sockaddr, &AF_INET, 0, $thisaddr);
4694 $that = pack($sockaddr, &AF_INET, $port, $thataddr);
4696 socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
4697 bind(S, $this) || die "bind: $!";
4698 connect(S, $that) || die "connect: $!";
4700 select(S); $| = 1; select(stdout);
4702 if ($child = fork) {
4716 And here's a server:
4720 $port = 2345 unless $port;
4722 require 'sys/socket.ph';
4724 $sockaddr = 'S n a4 x8';
4726 ($name, $aliases, $proto) = getprotobyname('tcp');
4727 ($name, $aliases, $port) = getservbyname($port, 'tcp')
4728 unless $port =~ /^\ed+$/;
4730 $this = pack($sockaddr, &AF_INET, $port, "\e0\e0\e0\e0");
4732 select(NS); $| = 1; select(stdout);
4734 socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
4735 bind(S, $this) || die "bind: $!";
4736 listen(S, 5) || die "connect: $!";
4738 select(S); $| = 1; select(stdout);
4741 print "Listening again\en";
4742 ($addr = accept(NS,S)) || die $!;
4743 print "accept ok\en";
4745 ($af,$port,$inetaddr) = unpack($sockaddr,$addr);
4746 @inetaddr = unpack('C4',$inetaddr);
4747 print "$af $port @inetaddr\en";
4756 .Sh "Predefined Names"
4757 The following names have special meaning to
4759 I could have used alphabetic symbols for some of these, but I didn't want
4760 to take the chance that someone would say reset \*(L"a\-zA\-Z\*(R" and wipe them all
4762 You'll just have to suffer along with these silly symbols.
4763 Most of them have reasonable mnemonics, or analogues in one of the shells.
4765 The default input and pattern-searching space.
4766 The following pairs are equivalent:
4770 while (<>) {\|.\|.\|. # only equivalent in while!
4771 while ($_ = <>) {\|.\|.\|.
4775 $_ \|=~ \|/\|^Subject:/
4786 (Mnemonic: underline is understood in certain operations.)
4788 The current input line number of the last filehandle that was read.
4790 Remember that only an explicit close on the filehandle resets the line number.
4791 Since <> never does an explicit close, line numbers increase across ARGV files
4792 (but see examples under eof).
4793 (Mnemonic: many programs use . to mean the current line number.)
4795 The input record separator, newline by default.
4798 RS variable, including treating blank lines as delimiters
4799 if set to the null string.
4800 You may set it to a multicharacter string to match a multi-character
4802 (Mnemonic: / is used to delimit line boundaries when quoting poetry.)
4804 The output field separator for the print operator.
4805 Ordinarily the print operator simply prints out the comma separated fields
4807 In order to get behavior more like
4809 set this variable as you would set
4811 OFS variable to specify what is printed between fields.
4812 (Mnemonic: what is printed when there is a , in your print statement.)
4814 This is like $, except that it applies to array values interpolated into
4815 a double-quoted string (or similar interpreted string).
4817 (Mnemonic: obvious, I think.)
4819 The output record separator for the print operator.
4820 Ordinarily the print operator simply prints out the comma separated fields
4821 you specify, with no trailing newline or record separator assumed.
4822 In order to get behavior more like
4824 set this variable as you would set
4826 ORS variable to specify what is printed at the end of the print.
4827 (Mnemonic: you set $\e instead of adding \en at the end of the print.
4828 Also, it's just like /, but it's what you get \*(L"back\*(R" from
4831 The output format for printed numbers.
4832 This variable is a half-hearted attempt to emulate
4835 There are times, however, when
4839 have differing notions of what
4841 Also, the initial value is %.20g rather than %.6g, so you need to set $#
4845 (Mnemonic: # is the number sign.)
4847 The current page number of the currently selected output channel.
4848 (Mnemonic: % is page number in nroff.)
4850 The current page length (printable lines) of the currently selected output
4853 (Mnemonic: = has horizontal lines.)
4855 The number of lines left on the page of the currently selected output channel.
4856 (Mnemonic: lines_on_page \- lines_printed.)
4858 The name of the current report format for the currently selected output
4860 Default is name of the filehandle.
4861 (Mnemonic: brother to $^.)
4863 The name of the current top-of-page format for the currently selected output
4865 Default is name of the filehandle with \*(L"_TOP\*(R" appended.
4866 (Mnemonic: points to top of page.)
4868 If set to nonzero, forces a flush after every write or print on the currently
4869 selected output channel.
4873 will typically be line buffered if output is to the
4874 terminal and block buffered otherwise.
4875 Setting this variable is useful primarily when you are outputting to a pipe,
4876 such as when you are running a
4878 script under rsh and want to see the
4879 output as it's happening.
4880 (Mnemonic: when you want your pipes to be piping hot.)
4882 The process number of the
4884 running this script.
4885 (Mnemonic: same as shells.)
4887 The status returned by the last pipe close, backtick (\`\`) command or
4890 Note that this is the status word returned by the wait() system
4891 call, so the exit value of the subprocess is actually ($? >> 8).
4892 $? & 255 gives which signal, if any, the process died from, and whether
4893 there was a core dump.
4894 (Mnemonic: similar to sh and ksh.)
4896 The string matched by the last pattern match (not counting any matches hidden
4897 within a BLOCK or eval enclosed by the current BLOCK).
4898 (Mnemonic: like & in some editors.)
4900 The string preceding whatever was matched by the last pattern match
4901 (not counting any matches hidden within a BLOCK or eval enclosed by the current
4903 (Mnemonic: \` often precedes a quoted string.)
4905 The string following whatever was matched by the last pattern match
4906 (not counting any matches hidden within a BLOCK or eval enclosed by the current
4908 (Mnemonic: \' often follows a quoted string.)
4915 print "$\`:$&:$\'\en"; # prints abc:def:ghi
4919 The last bracket matched by the last search pattern.
4920 This is useful if you don't know which of a set of alternative patterns
4925 /Version: \|(.*\|)|Revision: \|(.*\|)\|/ \|&& \|($rev = $+);
4928 (Mnemonic: be positive and forward looking.)
4930 Set to 1 to do multiline matching within a string, 0 to tell
4932 that it can assume that strings contain a single line, for the purpose
4933 of optimizing pattern matches.
4934 Pattern matches on strings containing multiple newlines can produce confusing
4935 results when $* is 0.
4937 (Mnemonic: * matches multiple things.)
4938 Note that this variable only influences the interpretation of ^ and $.
4939 A literal newline can be searched for even when $* == 0.
4941 Contains the name of the file containing the
4943 script being executed.
4944 Assigning to $0 modifies the argument area that the ps(1) program sees.
4945 (Mnemonic: same as sh and ksh.)
4947 Contains the subpattern from the corresponding set of parentheses in the last
4948 pattern matched, not counting patterns matched in nested blocks that have
4949 been exited already.
4950 (Mnemonic: like \edigit.)
4952 The index of the first element in an array, and of the first character in
4954 Default is 0, but you could set it to 1 to make
4959 when subscripting and when evaluating the index() and substr() functions.
4960 (Mnemonic: [ begins subscripts.)
4962 The string printed out when you say \*(L"perl -v\*(R".
4963 It can be used to determine at the beginning of a script whether the perl
4964 interpreter executing the script is in the right range of versions.
4965 If used in a numeric context, returns the version + patchlevel / 1000.
4970 # see if getc is available
4971 ($version,$patchlevel) =
4972 $] =~ /(\ed+\e.\ed+).*\enPatch level: (\ed+)/;
4973 print STDERR "(No filename completion available.)\en"
4974 if $version * 1000 + $patchlevel < 2016;
4976 or, used numerically,
4978 warn "No checksumming!\en" if $] < 3.019;
4981 (Mnemonic: Is this version of perl in the right bracket?)
4983 The subscript separator for multi-dimensional array emulation.
4984 If you refer to an associative array element as
4990 $foo{join($;, $a, $b, $c)}
4994 @foo{$a,$b,$c} # a slice\*(--note the @
4998 ($foo{$a},$foo{$b},$foo{$c})
5001 Default is "\e034", the same as SUBSEP in
5003 Note that if your keys contain binary data there might not be any safe
5005 (Mnemonic: comma (the syntactic subscript separator) is a semi-semicolon.
5006 Yeah, I know, it's pretty lame, but $, is already taken for something more
5009 If used in a numeric context, yields the current value of errno, with all the
5011 (This means that you shouldn't depend on the value of $! to be anything
5012 in particular unless you've gotten a specific error return indicating a
5014 If used in a string context, yields the corresponding system error string.
5015 You can assign to $! in order to set errno
5016 if, for instance, you want $! to return the string for error n, or you want
5017 to set the exit value for the die operator.
5018 (Mnemonic: What just went bang?)
5020 The perl syntax error message from the last eval command.
5021 If null, the last eval parsed and executed correctly (although the operations
5022 you invoked may have failed in the normal fashion).
5023 (Mnemonic: Where was the syntax error \*(L"at\*(R"?)
5025 The real uid of this process.
5026 (Mnemonic: it's the uid you came FROM, if you're running setuid.)
5028 The effective uid of this process.
5033 $< = $>; # set real uid to the effective uid
5034 ($<,$>) = ($>,$<); # swap real and effective uid
5037 (Mnemonic: it's the uid you went TO, if you're running setuid.)
5038 Note: $< and $> can only be swapped on machines supporting setreuid().
5040 The real gid of this process.
5041 If you are on a machine that supports membership in multiple groups
5042 simultaneously, gives a space separated list of groups you are in.
5043 The first number is the one returned by getgid(), and the subsequent ones
5044 by getgroups(), one of which may be the same as the first number.
5045 (Mnemonic: parentheses are used to GROUP things.
5046 The real gid is the group you LEFT, if you're running setgid.)
5048 The effective gid of this process.
5049 If you are on a machine that supports membership in multiple groups
5050 simultaneously, gives a space separated list of groups you are in.
5051 The first number is the one returned by getegid(), and the subsequent ones
5052 by getgroups(), one of which may be the same as the first number.
5053 (Mnemonic: parentheses are used to GROUP things.
5054 The effective gid is the group that's RIGHT for you, if you're running setgid.)
5056 Note: $<, $>, $( and $) can only be set on machines that support the
5057 corresponding set[re][ug]id() routine.
5058 $( and $) can only be swapped on machines supporting setregid().
5060 The current set of characters after which a string may be broken to
5061 fill continuation fields (starting with ^) in a format.
5062 Default is "\ \en-", to break on whitespace or hyphens.
5063 (Mnemonic: a \*(L"colon\*(R" in poetry is a part of a line.)
5065 The current value of the debugging flags.
5070 The maximum system file descriptor, ordinarily 2. System file descriptors
5071 are passed to subprocesses, while higher file descriptors are not.
5072 During an open, system file descriptors are preserved even if the open
5073 fails. Ordinary file descriptors are closed before the open is attempted.
5075 The current value of the inplace-edit extension.
5076 Use undef to disable inplace editing.
5081 The internal flag that the debugger clears so that it doesn't
5082 debug itself. You could conceivable disable debugging yourself
5085 The time at which the script began running, in seconds since the epoch.
5086 The values returned by the
5091 filetests are based on this value.
5093 The current value of the warning switch.
5094 (Mnemonic: related to the
5098 The name that Perl itself was executed as, from argv[0].
5100 contains the name of the current file when reading from <>.
5102 The array ARGV contains the command line arguments intended for the script.
5103 Note that $#ARGV is the generally number of arguments minus one, since
5104 $ARGV[0] is the first argument, NOT the command name.
5105 See $0 for the command name.
5107 The array INC contains the list of places to look for
5110 evaluated by the \*(L"do EXPR\*(R" command or the \*(L"require\*(R" command.
5111 It initially consists of the arguments to any
5113 command line switches, followed
5116 library, probably \*(L"/usr/local/lib/perl\*(R",
5117 followed by \*(L".\*(R", to represent the current directory.
5119 The associative array INC contains entries for each filename that has
5120 been included via \*(L"do\*(R" or \*(L"require\*(R".
5121 The key is the filename you specified, and the value is the location of
5122 the file actually found.
5123 The \*(L"require\*(R" command uses this array to determine whether
5124 a given file has already been included.
5126 The associative array ENV contains your current environment.
5127 Setting a value in ENV changes the environment for child processes.
5129 The associative array SIG is used to set signal handlers for various signals.
5134 sub handler { # 1st argument is signal name
5136 print "Caught a SIG$sig\-\|\-shutting down\en";
5141 $SIG{\'INT\'} = \'handler\';
5142 $SIG{\'QUIT\'} = \'handler\';
5144 $SIG{\'INT\'} = \'DEFAULT\'; # restore default action
5145 $SIG{\'QUIT\'} = \'IGNORE\'; # ignore SIGQUIT
5148 The SIG array only contains values for the signals actually set within
5151 Perl provides a mechanism for alternate namespaces to protect packages from
5152 stomping on each others variables.
5153 By default, a perl script starts compiling into the package known as \*(L"main\*(R".
5156 declaration, you can switch namespaces.
5157 The scope of the package declaration is from the declaration itself to the end
5158 of the enclosing block (the same scope as the local() operator).
5159 Typically it would be the first declaration in a file to be included by
5160 the \*(L"require\*(R" operator.
5161 You can switch into a package in more than one place; it merely influences
5162 which symbol table is used by the compiler for the rest of that block.
5163 You can refer to variables and filehandles in other packages by prefixing
5164 the identifier with the package name and a single quote.
5165 If the package name is null, the \*(L"main\*(R" package as assumed.
5167 Only identifiers starting with letters are stored in the packages symbol
5169 All other symbols are kept in package \*(L"main\*(R".
5170 In addition, the identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT, ENV, INC
5171 and SIG are forced to be in package \*(L"main\*(R", even when used for
5172 other purposes than their built-in one.
5173 Note also that, if you have a package called \*(L"m\*(R", \*(L"s\*(R"
5174 or \*(L"y\*(R", the you can't use the qualified form of an identifier since it
5175 will be interpreted instead as a pattern match, a substitution
5178 Eval'ed strings are compiled in the package in which the eval was compiled
5180 (Assignments to $SIG{}, however, assume the signal handler specified is in the
5182 Qualify the signal handler name if you wish to have a signal handler in
5184 For an example, examine perldb.pl in the perl library.
5185 It initially switches to the DB package so that the debugger doesn't interfere
5186 with variables in the script you are trying to debug.
5187 At various points, however, it temporarily switches back to the main package
5188 to evaluate various expressions in the context of the main package.
5190 The symbol table for a package happens to be stored in the associative array
5191 of that name prepended with an underscore.
5192 The value in each entry of the associative array is
5193 what you are referring to when you use the *name notation.
5194 In fact, the following have the same effect (in package main, anyway),
5195 though the first is more
5196 efficient because it does the symbol table lookups at compile time:
5201 local($_main{'foo'}) = $_main{'bar'};
5204 You can use this to print out all the variables in a package, for instance.
5205 Here is dumpvar.pl from the perl library:
5212 \& local(*stab) = eval("*_$package");
5213 \& while (($key,$val) = each(%stab)) {
5215 \& local(*entry) = $val;
5216 \& if (defined $entry) {
5217 \& print "\e$$key = '$entry'\en";
5220 \& if (defined @entry) {
5221 \& print "\e@$key = (\en";
5222 \& foreach $num ($[ .. $#entry) {
5223 \& print " $num\et'",$entry[$num],"'\en";
5228 \& if ($key ne "_$package" && defined %entry) {
5229 \& print "\e%$key = (\en";
5230 \& foreach $key (sort keys(%entry)) {
5231 \& print " $key\et'",$entry{$key},"'\en";
5240 Note that, even though the subroutine is compiled in package dumpvar, the
5241 name of the subroutine is qualified so that its name is inserted into package
5244 Each programmer will, of course, have his or her own preferences in regards
5245 to formatting, but there are some general guidelines that will make your
5246 programs easier to read.
5248 Just because you CAN do something a particular way doesn't mean that
5249 you SHOULD do it that way.
5251 is designed to give you several ways to do anything, so consider picking
5252 the most readable one.
5255 open(FOO,$foo) || die "Can't open $foo: $!";
5259 die "Can't open $foo: $!" unless open(FOO,$foo);
5261 because the second way hides the main point of the statement in a
5265 print "Starting analysis\en" if $verbose;
5269 $verbose && print "Starting analysis\en";
5271 since the main point isn't whether the user typed -v or not.
5273 Similarly, just because an operator lets you assume default arguments
5274 doesn't mean that you have to make use of the defaults.
5275 The defaults are there for lazy systems programmers writing one-shot
5277 If you want your program to be readable, consider supplying the argument.
5279 Along the same lines, just because you
5281 omit parentheses in many places doesn't mean that you ought to:
5284 return print reverse sort num values array;
5285 return print(reverse(sort num (values(%array))));
5288 When in doubt, parenthesize.
5289 At the very least it will let some poor schmuck bounce on the % key in vi.
5291 Even if you aren't in doubt, consider the mental welfare of the person who
5292 has to maintain the code after you, and who will probably put parens in
5295 Don't go through silly contortions to exit a loop at the top or the
5298 provides the "last" operator so you can exit in the middle.
5299 Just outdent it a little to make it more visible:
5313 Don't be afraid to use loop labels\*(--they're there to enhance readability as
5314 well as to allow multi-level loop breaks.
5317 For portability, when using features that may not be implemented on every
5318 machine, test the construct in an eval to see if it fails.
5319 If you know what version or patchlevel a particular feature was implemented,
5320 you can test $] to see if it will be there.
5322 Choose mnemonic identifiers.
5330 switch, your script will be run under a debugging monitor.
5331 It will halt before the first executable statement and ask you for a
5334 Prints out a help message.
5339 Executes until it reaches the beginning of another statement.
5342 Executes over subroutine calls, until it reaches the beginning of the
5346 Executes statements until it has finished the current subroutine.
5349 Executes until the next breakpoint is reached.
5351 Continue to the specified line.
5352 Inserts a one-time-only breakpoint at the specified line.
5355 .Ip "l min+incr" 12 4
5356 List incr+1 lines starting at min.
5357 If min is omitted, starts where last listing left off.
5358 If incr is omitted, previous value of incr is used.
5359 .Ip "l min-max" 12 4
5360 List lines in the indicated range.
5362 List just the indicated line.
5366 List previous window.
5368 List window around line.
5369 .Ip "l subname" 12 4
5371 If it's a long subroutine it just lists the beginning.
5372 Use \*(L"l\*(R" to list more.
5373 .Ip "/pattern/" 12 4
5374 Regular expression search forward for pattern; the final / is optional.
5375 .Ip "?pattern?" 12 4
5376 Regular expression search backward for pattern; the final ? is optional.
5378 List lines that have breakpoints or actions.
5380 Lists the names of all subroutines.
5382 Toggle trace mode on or off.
5383 .Ip "b line condition" 12 4
5385 If line is omitted, sets a breakpoint on the
5386 line that is about to be executed.
5387 If a condition is specified, it is evaluated each time the statement is
5388 reached and a breakpoint is taken only if the condition is true.
5389 Breakpoints may only be set on lines that begin an executable statement.
5390 .Ip "b subname condition" 12 4
5391 Set breakpoint at first executable line of subroutine.
5394 If line is omitted, deletes the breakpoint on the
5395 line that is about to be executed.
5397 Delete all breakpoints.
5398 .Ip "a line command" 12 4
5399 Set an action for line.
5400 A multi-line command may be entered by backslashing the newlines.
5402 Delete all line actions.
5403 .Ip "< command" 12 4
5404 Set an action to happen before every debugger prompt.
5405 A multi-line command may be entered by backslashing the newlines.
5406 .Ip "> command" 12 4
5407 Set an action to happen after the prompt when you've just given a command
5408 to return to executing the script.
5409 A multi-line command may be entered by backslashing the newlines.
5410 .Ip "V package" 12 4
5411 List all variables in package.
5412 Default is main package.
5414 Redo a debugging command.
5415 If number is omitted, redoes the previous command.
5416 .Ip "! -number" 12 4
5417 Redo the command that was that many commands ago.
5418 .Ip "H -number" 12 4
5419 Display last n commands.
5420 Only commands longer than one character are listed.
5421 If number is omitted, lists them all.
5425 Execute command as a perl statement.
5426 A missing semicolon will be supplied.
5428 Same as \*(L"print DB'OUT expr\*(R".
5429 The DB'OUT filehandle is opened to /dev/tty, regardless of where STDOUT
5430 may be redirected to.
5432 If you want to modify the debugger, copy perldb.pl from the perl library
5433 to your current directory and modify it as necessary.
5434 (You'll also have to put -I. on your command line.)
5435 You can do some customization by setting up a .perldb file which contains
5436 initialization code.
5437 For instance, you could make aliases like these:
5440 $DB'alias{'len'} = 's/^len(.*)/p length($1)/';
5441 $DB'alias{'stop'} = 's/^stop (at|in)/b/';
5443 's/^\e./p "\e$DB\e'sub(\e$DB\e'line):\et",\e$DB\e'line[\e$DB\e'line]/';
5446 .Sh "Setuid Scripts"
5448 is designed to make it easy to write secure setuid and setgid scripts.
5449 Unlike shells, which are based on multiple substitution passes on each line
5452 uses a more conventional evaluation scheme with fewer hidden \*(L"gotchas\*(R".
5453 Additionally, since the language has more built-in functionality, it
5454 has to rely less upon external (and possibly untrustworthy) programs to
5455 accomplish its purposes.
5457 In an unpatched 4.2 or 4.3bsd kernel, setuid scripts are intrinsically
5458 insecure, but this kernel feature can be disabled.
5461 can emulate the setuid and setgid mechanism when it notices the otherwise
5462 useless setuid/gid bits on perl scripts.
5463 If the kernel feature isn't disabled,
5465 will complain loudly that your setuid script is insecure.
5466 You'll need to either disable the kernel setuid script feature, or put
5467 a C wrapper around the script.
5469 When perl is executing a setuid script, it takes special precautions to
5470 prevent you from falling into any obvious traps.
5471 (In some ways, a perl script is more secure than the corresponding
5473 Any command line argument, environment variable, or input is marked as
5474 \*(L"tainted\*(R", and may not be used, directly or indirectly, in any
5475 command that invokes a subshell, or in any command that modifies files,
5476 directories or processes.
5477 Any variable that is set within an expression that has previously referenced
5478 a tainted value also becomes tainted (even if it is logically impossible
5479 for the tainted value to influence the variable).
5484 $foo = shift; # $foo is tainted
5485 $bar = $foo,\'bar\'; # $bar is also tainted
5486 $xxx = <>; # Tainted
5487 $path = $ENV{\'PATH\'}; # Tainted, but see below
5488 $abc = \'abc\'; # Not tainted
5491 system "echo $foo"; # Insecure
5492 system "/bin/echo", $foo; # Secure (doesn't use sh)
5493 system "echo $bar"; # Insecure
5494 system "echo $abc"; # Insecure until PATH set
5497 $ENV{\'PATH\'} = \'/bin:/usr/bin\';
5498 $ENV{\'IFS\'} = \'\' if $ENV{\'IFS\'} ne \'\';
5500 $path = $ENV{\'PATH\'}; # Not tainted
5501 system "echo $abc"; # Is secure now!
5504 open(FOO,"$foo"); # OK
5505 open(FOO,">$foo"); # Not OK
5507 open(FOO,"echo $foo|"); # Not OK, but...
5508 open(FOO,"-|") || exec \'echo\', $foo; # OK
5510 $zzz = `echo $foo`; # Insecure, zzz tainted
5512 unlink $abc,$foo; # Insecure
5513 umask $foo; # Insecure
5516 exec "echo $foo"; # Insecure
5517 exec "echo", $foo; # Secure (doesn't use sh)
5518 exec "sh", \'-c\', $foo; # Considered secure, alas
5521 The taintedness is associated with each scalar value, so some elements
5522 of an array can be tainted, and others not.
5524 If you try to do something insecure, you will get a fatal error saying
5525 something like \*(L"Insecure dependency\*(R" or \*(L"Insecure PATH\*(R".
5526 Note that you can still write an insecure system call or exec,
5527 but only by explicitly doing something like the last example above.
5528 You can also bypass the tainting mechanism by referencing
5531 presumes that if you reference a substring using $1, $2, etc, you knew
5532 what you were doing when you wrote the pattern:
5535 $ARGV[0] =~ /^\-P(\ew+)$/;
5536 $printer = $1; # Not tainted
5539 This is fairly secure since \ew+ doesn't match shell metacharacters.
5540 Use of .+ would have been insecure, but
5542 doesn't check for that, so you must be careful with your patterns.
5543 This is the ONLY mechanism for untainting user supplied filenames if you
5544 want to do file operations on them (unless you make $> equal to $<).
5546 It's also possible to get into trouble with other operations that don't care
5547 whether they use tainted values.
5548 Make judicious use of the file tests in dealing with any user-supplied
5550 When possible, do opens and such after setting $> = $<.
5552 doesn't prevent you from opening tainted filenames for reading, so be
5553 careful what you print out.
5554 The tainting mechanism is intended to prevent stupid mistakes, not to remove
5555 the need for thought.
5558 uses PATH in executing subprocesses, and in finding the script if \-S
5560 HOME or LOGDIR are used if chdir has no argument.
5564 uses no environment variables, except to make them available
5565 to the script being executed, and to child processes.
5566 However, scripts running setuid would do well to execute the following lines
5567 before doing anything else, just to keep people honest:
5571 $ENV{\'PATH\'} = \'/bin:/usr/bin\'; # or whatever you need
5572 $ENV{\'SHELL\'} = \'/bin/sh\' if $ENV{\'SHELL\'} ne \'\';
5573 $ENV{\'IFS\'} = \'\' if $ENV{\'IFS\'} ne \'\';
5577 Larry Wall <lwall@jpl-devvax.Jpl.Nasa.Gov>
5579 MS-DOS port by Diomidis Spinellis <dds@cc.ic.ac.uk>
5581 /tmp/perl\-eXXXXXX temporary file for
5585 a2p awk to perl translator
5587 s2p sed to perl translator
5589 Compilation errors will tell you the line number of the error, with an
5590 indication of the next token or token type that was to be examined.
5591 (In the case of a script passed to
5597 is counted as one line.)
5599 Setuid scripts have additional constraints that can produce error messages
5600 such as \*(L"Insecure dependency\*(R".
5601 See the section on setuid scripts.
5605 users should take special note of the following:
5607 Semicolons are required after all simple statements in
5610 is not a statement delimiter.
5612 Curly brackets are required on ifs and whiles.
5614 Variables begin with $ or @ in
5617 Arrays index from 0 unless you set $[.
5618 Likewise string positions in substr() and index().
5620 You have to decide whether your array has numeric or string indices.
5622 Associative array values do not spring into existence upon mere reference.
5624 You have to decide whether you want to use string or numeric comparisons.
5626 Reading an input line does not split it for you. You get to split it yourself
5630 operator has different arguments.
5632 The current input line is normally in $_, not $0.
5633 It generally does not have the newline stripped.
5634 ($0 is the name of the program executed.)
5636 $<digit> does not refer to fields\*(--it refers to substrings matched by the last
5641 statement does not add field and record separators unless you set
5644 You must open your files before you print to them.
5646 The range operator is \*(L".\|.\*(R", not comma.
5647 (The comma operator works as in C.)
5649 The match operator is \*(L"=~\*(R", not \*(L"~\*(R".
5650 (\*(L"~\*(R" is the one's complement operator, as in C.)
5652 The exponentiation operator is \*(L"**\*(R", not \*(L"^\*(R".
5653 (\*(L"^\*(R" is the XOR operator, as in C.)
5655 The concatenation operator is \*(L".\*(R", not the null string.
5656 (Using the null string would render \*(L"/pat/ /pat/\*(R" unparsable,
5657 since the third slash would be interpreted as a division operator\*(--the
5658 tokener is in fact slightly context sensitive for operators like /, ?, and <.
5659 And in fact, . itself can be the beginning of a number.)
5667 The following variables work differently
5671 ARGC \h'|2.5i'$#ARGV
5673 FILENAME\h'|2.5i'$ARGV
5674 FNR \h'|2.5i'$. \- something
5675 FS \h'|2.5i'(whatever you like)
5676 NF \h'|2.5i'$#Fld, or some such
5681 RLENGTH \h'|2.5i'length($&)
5683 RSTART \h'|2.5i'length($\`)
5688 When in doubt, run the
5690 construct through a2p and see what it gives you.
5692 Cerebral C programmers should take note of the following:
5694 Curly brackets are required on ifs and whiles.
5696 You should use \*(L"elsif\*(R" rather than \*(L"else if\*(R"
5707 There's no switch statement.
5709 Variables begin with $ or @ in
5712 Printf does not implement *.
5714 Comments begin with #, not /*.
5716 You can't take the address of anything.
5718 ARGV must be capitalized.
5720 The \*(L"system\*(R" calls link, unlink, rename, etc. return nonzero for success, not 0.
5722 Signal handlers deal with signal names, not numbers.
5726 programmers should take note of the following:
5728 Backreferences in substitutions use $ rather than \e.
5730 The pattern matching metacharacters (, ), and | do not have backslashes in front.
5732 The range operator is .\|. rather than comma.
5734 Sharp shell programmers should take note of the following:
5736 The backtick operator does variable interpretation without regard to the
5737 presence of single quotes in the command.
5739 The backtick operator does no translation of the return value, unlike csh.
5741 Shells (especially csh) do several levels of substitution on each command line.
5743 does substitution only in certain constructs such as double quotes,
5744 backticks, angle brackets and search patterns.
5746 Shells interpret scripts a little bit at a time.
5748 compiles the whole program before executing it.
5750 The arguments are available via @ARGV, not $1, $2, etc.
5752 The environment is not automatically made available as variables.
5753 .SH ERRATA\0AND\0ADDENDA
5755 .I Programming\0Perl ,
5756 has the following omissions and goofs.
5758 On page 5, the examples which read
5765 eval "exec /usr/bin/perl
5769 On page 195, the equivalent to the System V sum program only works for
5770 very small files. To do larger files, use
5774 $checksum = unpack("%32C*",<>) % 32767;
5780 switch to set the initial value of $/ was added to Perl after the book
5785 switch now does automatic line ending processing.
5787 The qx// construct is now a synonym for backticks.
5789 $0 may now be assigned to set the argument displayed by
5792 The new @###.## format was omitted accidentally from the description
5795 It wasn't known at press time that s///ee caused multiple evaluations of
5796 the replacement expression. This is to be construed as a feature.
5798 (LIST) x $count now does array replication.
5800 There is now no limit on the number of parentheses in a regular expression.
5802 In double-quote context, more escapes are supported: \ee, \ea, \ex1b, \ec[,
5803 \el, \eL, \eu, \eU, \eE. The latter five control up/lower case translation.
5807 variable may now be set to a multi-character delimiter.
5809 There is now a g modifier on ordinary pattern matching that causes it
5810 to iterate through a string finding multiple matches.
5812 All of the $^X variables are new except for $^T.
5816 is at the mercy of your machine's definitions of various operations
5817 such as type casting, atof() and sprintf().
5819 If your stdio requires an seek or eof between reads and writes on a particular
5822 (This doesn't apply to sysread() and syswrite().)
5824 While none of the built-in data types have any arbitrary size limits (apart
5825 from memory size), there are still a few arbitrary limits:
5826 a given identifier may not be longer than 255 characters;
5827 sprintf is limited on many machines to 128 characters per field (unless the format
5828 specifier is exactly %s);
5829 and no component of your PATH may be longer than 255 if you use \-S.
5832 actually stands for Pathologically Eclectic Rubbish Lister, but don't tell