2 ''' $Header: perl_man.1,v 3.0.1.5 90/03/27 16:14:37 lwall Locked $
4 ''' $Log: perl.man.1,v $
5 ''' Revision 3.0.1.5 90/03/27 16:14:37 lwall
6 ''' patch16: .. now works using magical string increment
8 ''' Revision 3.0.1.4 90/03/12 16:44:33 lwall
9 ''' patch13: (LIST,) now legal
10 ''' patch13: improved LIST documentation
11 ''' patch13: example of if-elsif switch was wrong
13 ''' Revision 3.0.1.3 90/02/28 17:54:32 lwall
14 ''' patch9: @array in scalar context now returns length of array
15 ''' patch9: in manual, example of open and ?: was backwards
17 ''' Revision 3.0.1.2 89/11/17 15:30:03 lwall
18 ''' patch5: fixed some manual typos and indent problems
20 ''' Revision 3.0.1.1 89/11/11 04:41:22 lwall
21 ''' patch2: explained about sh and ${1+"$@"}
22 ''' patch2: documented that space must separate word and '' string
24 ''' Revision 3.0 89/10/18 15:21:29 lwall
46 ''' Set up \*(-- to give an unbreakable dash;
47 ''' string Tr holds user defined translation string.
48 ''' Bell System Logo is used as a dummy character.
53 .if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
54 .if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
71 perl \- Practical Extraction and Report Language
74 [options] filename args
77 is an interpreted language optimized for scanning arbitrary text files,
78 extracting information from those text files, and printing reports based
80 It's also a good language for many system management tasks.
81 The language is intended to be practical (easy to use, efficient, complete)
82 rather than beautiful (tiny, elegant, minimal).
83 It combines (in the author's opinion, anyway) some of the best features of C,
84 \fIsed\fR, \fIawk\fR, and \fIsh\fR,
85 so people familiar with those languages should have little difficulty with it.
86 (Language historians will also note some vestiges of \fIcsh\fR, Pascal, and
88 Expression syntax corresponds quite closely to C expression syntax.
89 Unlike most Unix utilities,
91 does not arbitrarily limit the size of your data\*(--if you've got
94 can slurp in your whole file as a single string.
95 Recursion is of unlimited depth.
96 And the hash tables used by associative arrays grow as necessary to prevent
99 uses sophisticated pattern matching techniques to scan large amounts of
101 Although optimized for scanning text,
103 can also deal with binary data, and can make dbm files look like associative
104 arrays (where dbm is available).
107 scripts are safer than C programs
108 through a dataflow tracing mechanism which prevents many stupid security holes.
109 If you have a problem that would ordinarily use \fIsed\fR
110 or \fIawk\fR or \fIsh\fR, but it
111 exceeds their capabilities or must run a little faster,
112 and you don't want to write the silly thing in C, then
115 There are also translators to turn your
126 looks for your script in one of the following places:
128 Specified line by line via
130 switches on the command line.
132 Contained in the file specified by the first filename on the command line.
133 (Note that systems supporting the #! notation invoke interpreters this way.)
135 Passed in implicitly via standard input.
136 This only works if there are no filename arguments\*(--to pass
139 script you must explicitly specify a \- for the script name.
141 After locating your script,
143 compiles it to an internal form.
144 If the script is syntactically correct, it is executed.
146 Note: on first reading this section may not make much sense to you. It's here
147 at the front for easy reference.
149 A single-character option may be combined with the following option, if any.
150 This is particularly useful when invoking a script using the #! construct which
151 only allows one argument. Example:
155 #!/usr/bin/perl \-spi.bak # same as \-s \-p \-i.bak
162 turns on autosplit mode when used with a
166 An implicit split command to the @F array
167 is done as the first thing inside the implicit while loop produced by
174 perl \-ane \'print pop(@F), "\en";\'
180 print pop(@F), "\en";
186 runs the script under the perl debugger.
187 See the section on Debugging.
190 sets debugging flags.
191 To watch how it executes your script, use
193 (This only works if debugging is compiled into your
195 Another nice value is \-D1024, which lists your compiled syntax tree.
196 And \-D512 displays compiled regular expressions.
198 .BI \-e " commandline"
199 may be used to enter one line of script.
202 commands may be given to build up a multi-line script.
207 will not look for a script filename in the argument list.
210 specifies that files processed by the <> construct are to be edited
212 It does this by renaming the input file, opening the output file by the
213 same name, and selecting that output file as the default for print statements.
214 The extension, if supplied, is added to the name of the
215 old file to make a backup copy.
216 If no extension is supplied, no backup is made.
217 Saying \*(L"perl \-p \-i.bak \-e "s/foo/bar/;" .\|.\|. \*(R" is the same as using
222 #!/usr/bin/perl \-pi.bak
225 which is equivalent to
230 if ($ARGV ne $oldargv) {
231 rename($ARGV, $ARGV . \'.bak\');
232 open(ARGVOUT, ">$ARGV");
239 print; # this prints to original filename
246 form doesn't need to compare $ARGV to $oldargv to know when
247 the filename has changed.
248 It does, however, use ARGVOUT for the selected filehandle.
251 is restored as the default output filehandle after the loop.
253 You can use eof to locate the end of each input file, in case you want
254 to append to each file, or reset line numbering (see example under eof).
257 may be used in conjunction with
259 to tell the C preprocessor where to look for include files.
260 By default /usr/include and /usr/lib/perl are searched.
265 to assume the following loop around your script, which makes it iterate
266 over filename arguments somewhat like \*(L"sed \-n\*(R" or \fIawk\fR:
271 .\|.\|. # your script goes here
275 Note that the lines are not printed by default.
278 to have lines printed.
279 Here is an efficient way to delete all files older than a week:
282 find . \-mtime +7 \-print | perl \-ne \'chop;unlink;\'
285 This is faster than using the \-exec switch of find because you don't have to
286 start a process on every filename found.
291 to assume the following loop around your script, which makes it iterate
292 over filename arguments somewhat like \fIsed\fR:
297 .\|.\|. # your script goes here
303 Note that the lines are printed automatically.
304 To suppress printing use the
314 causes your script to be run through the C preprocessor before
317 (Since both comments and cpp directives begin with the # character,
318 you should avoid starting comments with any words recognized
319 by the C preprocessor such as \*(L"if\*(R", \*(L"else\*(R" or \*(L"define\*(R".)
322 enables some rudimentary switch parsing for switches on the command line
323 after the script name but before any filename arguments (or before a \-\|\-).
324 Any switch found there is removed from @ARGV and sets the corresponding variable in the
327 The following script prints \*(L"true\*(R" if and only if the script is
328 invoked with a \-xyz switch.
333 if ($xyz) { print "true\en"; }
340 use the PATH environment variable to search for the script
341 (unless the name of the script starts with a slash).
342 Typically this is used to emulate #! startup on machines that don't
343 support #!, in the following manner:
347 eval "exec /usr/bin/perl \-S $0 $*"
348 if $running_under_some_shell;
351 The system ignores the first line and feeds the script to /bin/sh,
352 which proceeds to try to execute the
354 script as a shell script.
355 The shell executes the second line as a normal shell command, and thus
359 On some systems $0 doesn't always contain the full pathname,
364 to search for the script if necessary.
367 locates the script, it parses the lines and ignores them because
368 the variable $running_under_some_shell is never true.
369 A better construct than $* would be ${1+"$@"}, which handles embedded spaces
370 and such in the filenames, but doesn't work if the script is being interpreted
372 In order to start up sh rather than csh, some systems may have to replace the
373 #! line with a line containing just
374 a colon, which will be politely ignored by perl.
379 to dump core after compiling your script.
380 You can then take this core dump and turn it into an executable file
381 by using the undump program (not supplied).
382 This speeds startup at the expense of some disk space (which you can
383 minimize by stripping the executable).
384 (Still, a "hello world" executable comes out to about 200K on my machine.)
385 If you are going to run your executable as a set-id program then you
386 should probably compile it using taintperl rather than normal perl.
387 If you want to execute a portion of your script before dumping, use the
388 dump operator instead.
393 to do unsafe operations.
394 Currently the only \*(L"unsafe\*(R" operation is the unlinking of directories while
395 running as superuser.
398 prints the version and patchlevel of your
403 prints warnings about identifiers that are mentioned only once, and scalar
404 variables that are used before being set.
405 Also warns about redefined subroutines, and references to undefined
406 filehandles or filehandles opened readonly that you are attempting to
408 Also warns you if you use == on values that don't look like numbers, and if
409 your subroutines recurse more than 100 deep.
410 .Sh "Data Types and Objects"
413 has three data types: scalars, arrays of scalars, and
414 associative arrays of scalars.
415 Normal arrays are indexed by number, and associative arrays by string.
417 The interpretation of operations and values in perl sometimes
418 depends on the requirements
419 of the context around the operation or value.
420 There are three major contexts: string, numeric and array.
421 Certain operations return array values
422 in contexts wanting an array, and scalar values otherwise.
423 (If this is true of an operation it will be mentioned in the documentation
425 Operations which return scalars don't care whether the context is looking
426 for a string or a number, but
427 scalar variables and values are interpreted as strings or numbers
428 as appropriate to the context.
429 A scalar is interpreted as TRUE in the boolean sense if it is not the null
431 Booleans returned by operators are 1 for true and 0 or \'\' (the null
434 There are actually two varieties of null string: defined and undefined.
435 Undefined null strings are returned when there is no real value for something,
436 such as when there was an error, or at end of file, or when you refer
437 to an uninitialized variable or element of an array.
438 An undefined null string may become defined the first time you access it, but
439 prior to that you can use the defined() operator to determine whether the
440 value is defined or not.
442 References to scalar variables always begin with \*(L'$\*(R', even when referring
443 to a scalar that is part of an array.
448 $days \h'|2i'# a simple scalar variable
449 $days[28] \h'|2i'# 29th element of array @days
450 $days{\'Feb\'}\h'|2i'# one value from an associative array
451 $#days \h'|2i'# last index of array @days
453 but entire arrays or array slices are denoted by \*(L'@\*(R':
455 @days \h'|2i'# ($days[0], $days[1],\|.\|.\|. $days[n])
456 @days[3,4,5]\h'|2i'# same as @days[3.\|.5]
457 @days{'a','c'}\h'|2i'# same as ($days{'a'},$days{'c'})
459 and entire associative arrays are denoted by \*(L'%\*(R':
461 %days \h'|2i'# (key1, val1, key2, val2 .\|.\|.)
464 Any of these eight constructs may serve as an lvalue,
465 that is, may be assigned to.
466 (It also turns out that an assignment is itself an lvalue in
467 certain contexts\*(--see examples under s, tr and chop.)
468 Assignment to a scalar evaluates the righthand side in a scalar context,
469 while assignment to an array or array slice evaluates the righthand side
472 You may find the length of array @days by evaluating
473 \*(L"$#days\*(R", as in
475 (Actually, it's not the length of the array, it's the subscript of the last element, since there is (ordinarily) a 0th element.)
476 Assigning to $#days changes the length of the array.
477 Shortening an array by this method does not actually destroy any values.
478 Lengthening an array that was previously shortened recovers the values that
479 were in those elements.
480 You can also gain some measure of efficiency by preextending an array that
482 (You can also extend an array by assigning to an element that is off the
484 This differs from assigning to $#whatever in that intervening values
485 are set to null rather than recovered.)
486 You can truncate an array down to nothing by assigning the null list () to
488 The following are exactly equivalent
492 $#whatever = $[ \- 1;
496 If you evaluate an array in a scalar context, it returns the length of
498 The following is always true:
501 @whatever == $#whatever \- $[ + 1;
505 Multi-dimensional arrays are not directly supported, but see the discussion
506 of the $; variable later for a means of emulating multiple subscripts with
507 an associative array.
508 You could also write a subroutine to turn multiple subscripts into a single
511 Every data type has its own namespace.
512 You can, without fear of conflict, use the same name for a scalar variable,
513 an array, an associative array, a filehandle, a subroutine name, and/or
515 Since variable and array references always start with \*(L'$\*(R', \*(L'@\*(R',
516 or \*(L'%\*(R', the \*(L"reserved\*(R" words aren't in fact reserved
517 with respect to variable names.
518 (They ARE reserved with respect to labels and filehandles, however, which
519 don't have an initial special character.
520 Hint: you could say open(LOG,\'logfile\') rather than open(log,\'logfile\').
521 Using uppercase filehandles also improves readability and protects you
522 from conflict with future reserved words.)
523 Case IS significant\*(--\*(L"FOO\*(R", \*(L"Foo\*(R" and \*(L"foo\*(R" are all
525 Names which start with a letter may also contain digits and underscores.
526 Names which do not start with a letter are limited to one character,
527 e.g. \*(L"$%\*(R" or \*(L"$$\*(R".
528 (Most of the one character names have a predefined significance to
532 Numeric literals are specified in any of the usual floating point or
544 String literals are delimited by either single or double quotes.
545 They work much like shell quotes:
546 double-quoted string literals are subject to backslash and variable
547 substitution; single-quoted strings are not (except for \e\' and \e\e).
548 The usual backslash rules apply for making characters such as newline, tab, etc.
549 You can also embed newlines directly in your strings, i.e. they can end on
550 a different line than they begin.
551 This is nice, but if you forget your trailing quote, the error will not be
554 finds another line containing the quote character, which
555 may be much further on in the script.
556 Variable substitution inside strings is limited to scalar variables, normal
557 array values, and array slices.
558 (In other words, identifiers beginning with $ or @, followed by an optional
559 bracketed expression as a subscript.)
560 The following code segment prints out \*(L"The price is $100.\*(R"
564 $Price = \'$100\';\h'|3.5i'# not interpreted
565 print "The price is $Price.\e\|n";\h'|3.5i'# interpreted
568 Note that you can put curly brackets around the identifier to delimit it
569 from following alphanumerics.
570 Also note that a single quoted string must be separated from a preceding
571 word by a space, since single quote is a valid character in an identifier
574 Array values are interpolated into double-quoted strings by joining all the
575 elements of the array with the delimiter specified in the $" variable,
577 (Since in versions of perl prior to 3.0 the @ character was not a metacharacter
578 in double-quoted strings, the interpolation of @array, $array[EXPR],
579 @array[LIST], $array{EXPR}, or @array{LIST} only happens if array is
580 referenced elsewhere in the program or is predefined.)
581 The following are equivalent:
585 $temp = join($",@ARGV);
591 Within search patterns (which also undergo double-quotish substitution)
592 there is a bad ambiguity: Is /$foo[bar]/ to be
593 interpreted as /${foo}[bar]/ (where [bar] is a character class for the
594 regular expression) or as /${foo[bar]}/ (where [bar] is the subscript to
596 If @foo doesn't otherwise exist, then it's obviously a character class.
597 If @foo exists, perl takes a good guess about [bar], and is almost always right.
598 If it does guess wrong, or if you're just plain paranoid,
599 you can force the correct interpretation with curly brackets as above.
601 A line-oriented form of quoting is based on the shell here-is syntax.
602 Following a << you specify a string to terminate the quoted material, and all lines
603 following the current line down to the terminating string are the value
605 The terminating string may be either an identifier (a word), or some
607 If quoted, the type of quotes you use determines the treatment of the text,
608 just as in regular quoting.
609 An unquoted identifier works like double quotes.
610 There must be no space between the << and the identifier.
611 (If you put a space it will be treated as a null identifier, which is
612 valid, and matches the first blank line\*(--see Merry Christmas example below.)
613 The terminating string must appear by itself (unquoted and with no surrounding
614 whitespace) on the terminating line.
617 print <<EOF; # same as above
621 print <<"EOF"; # same as above
625 print << x 10; # null identifier is delimiter
628 print <<`EOC`; # execute commands
633 print <<foo, <<bar; # you can stack them
640 Array literals are denoted by separating individual values by commas, and
641 enclosing the list in parentheses:
647 In a context not requiring an array value, the value of the array literal
648 is the value of the final element, as in the C comma operator.
653 @foo = (\'cc\', \'\-E\', $bar);
655 assigns the entire array value to array foo, but
657 $foo = (\'cc\', \'\-E\', $bar);
660 assigns the value of variable bar to variable foo.
661 Note that the value of an actual array in a scalar context is the length
662 of the array; the following assigns to $foo the value 3:
666 @foo = (\'cc\', \'\-E\', $bar);
667 $foo = @foo; # $foo gets 3
670 You may have an optional comma before the closing parenthesis of an
671 array literal, so that you can say:
681 When a LIST is evaluated, each element of the list is evaluated in
682 an array context, and the resulting array value is interpolated into LIST
683 just as if each individual element were a member of LIST. Thus arrays
684 lose their identity in a LIST\*(--the list
688 contains all the elements of @foo followed by all the elements of @bar,
689 followed by all the elements returned by the subroutine named SomeSub.
691 A list value may also be subscripted like a normal array.
695 $time = (stat($file))[8]; # stat returns array value
696 $digit = ('a','b','c','d','e','f')[$digit-10];
697 return (pop(@foo),pop(@foo))[0];
701 Array lists may be assigned to if and only if each element of the list
705 ($a, $b, $c) = (1, 2, 3);
707 ($map{\'red\'}, $map{\'blue\'}, $map{\'green\'}) = (0x00f, 0x0f0, 0xf00);
709 The final element may be an array or an associative array:
711 ($a, $b, @rest) = split;
712 local($a, $b, %rest) = @_;
715 You can actually put an array anywhere in the list, but the first array
716 in the list will soak up all the values, and anything after it will get
718 This may be useful in a local().
720 An associative array literal contains pairs of values to be interpreted
721 as a key and a value:
725 # same as map assignment above
726 %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
729 Array assignment in a scalar context returns the number of elements
730 produced by the expression on the right side of the assignment:
733 $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
737 There are several other pseudo-literals that you should know about.
738 If a string is enclosed by backticks (grave accents), it first undergoes
739 variable substitution just like a double quoted string.
740 It is then interpreted as a command, and the output of that command
741 is the value of the pseudo-literal, like in a shell.
742 The command is executed each time the pseudo-literal is evaluated.
743 The status value of the command is returned in $? (see Predefined Names
744 for the interpretation of $?).
745 Unlike in \f2csh\f1, no translation is done on the return
746 data\*(--newlines remain newlines.
747 Unlike in any of the shells, single quotes do not hide variable names
748 in the command from interpretation.
749 To pass a $ through to the shell you need to hide it with a backslash.
751 Evaluating a filehandle in angle brackets yields the next line
752 from that file (newline included, so it's never false until EOF, at
753 which time an undefined value is returned).
754 Ordinarily you must assign that value to a variable,
755 but there is one situation where an automatic assignment happens.
756 If (and only if) the input symbol is the only thing inside the conditional of a
759 automatically assigned to the variable \*(L"$_\*(R".
760 (This may seem like an odd thing to you, but you'll use the construct
764 Anyway, the following lines are equivalent to each other:
768 while ($_ = <STDIN>) { print; }
769 while (<STDIN>) { print; }
770 for (\|;\|<STDIN>;\|) { print; }
771 print while $_ = <STDIN>;
786 will also work except in packages, where they would be interpreted as
787 local identifiers rather than global.)
788 Additional filehandles may be created with the
792 If a <FILEHANDLE> is used in a context that is looking for an array, an array
793 consisting of all the input lines is returned, one line per array element.
794 It's easy to make a LARGE data space this way, so use with care.
796 The null filehandle <> is special and can be used to emulate the behavior of
797 \fIsed\fR and \fIawk\fR.
798 Input from <> comes either from standard input, or from each file listed on
800 Here's how it works: the first time <> is evaluated, the ARGV array is checked,
801 and if it is null, $ARGV[0] is set to \'-\', which when opened gives you standard
803 The ARGV array is then processed as a list of filenames.
809 .\|.\|. # code for each line
815 unshift(@ARGV, \'\-\') \|if \|$#ARGV < $[;
816 while ($ARGV = shift) {
819 .\|.\|. # code for each line
824 except that it isn't as cumbersome to say.
825 It really does shift array ARGV and put the current filename into
827 It also uses filehandle ARGV internally.
828 You can modify @ARGV before the first <> as long as you leave the first
829 filename at the beginning of the array.
830 Line numbers ($.) continue as if the input was one big happy file.
831 (But see example under eof for how to reset line numbers on each file.)
834 If you want to set @ARGV to your own list of files, go right ahead.
835 If you want to pass switches into your script, you can
836 put a loop on the front like this:
840 while ($_ = $ARGV[0], /\|^\-/\|) {
842 last if /\|^\-\|\-$\|/\|;
843 /\|^\-D\|(.*\|)/ \|&& \|($debug = $1);
844 /\|^\-v\|/ \|&& \|$verbose++;
845 .\|.\|. # other switches
848 .\|.\|. # code for each line
852 The <> symbol will return FALSE only once.
853 If you call it again after this it will assume you are processing another
854 @ARGV list, and if you haven't set @ARGV, will input from
857 If the string inside the angle brackets is a reference to a scalar variable
859 then that variable contains the name of the filehandle to input from.
861 If the string inside angle brackets is not a filehandle, it is interpreted
862 as a filename pattern to be globbed, and either an array of filenames or the
863 next filename in the list is returned, depending on context.
864 One level of $ interpretation is done first, but you can't say <$foo>
865 because that's an indirect filehandle as explained in the previous
867 You could insert curly brackets to force interpretation as a
868 filename glob: <${foo}>.
880 open(foo, "echo *.c | tr \-s \' \et\er\ef\' \'\e\e012\e\e012\e\e012\e\e012\'|");
887 In fact, it's currently implemented that way.
888 (Which means it will not work on filenames with spaces in them unless
889 you have /bin/csh on your machine.)
890 Of course, the shortest way to do the above is:
900 script consists of a sequence of declarations and commands.
901 The only things that need to be declared in
903 are report formats and subroutines.
904 See the sections below for more information on those declarations.
905 All uninitialized user-created objects are assumed to
906 start with a null or 0 value until they
907 are defined by some explicit operation such as assignment.
908 The sequence of commands is executed just once, unlike in
912 scripts, where the sequence of commands is executed for each input line.
913 While this means that you must explicitly loop over the lines of your input file
914 (or files), it also means you have much more control over which files and which
916 (Actually, I'm lying\*(--it is possible to do an implicit loop with either the
922 A declaration can be put anywhere a command can, but has no effect on the
923 execution of the primary sequence of commands--declarations all take effect
925 Typically all the declarations are put at the beginning or the end of the script.
928 is, for the most part, a free-form language.
929 (The only exception to this is format declarations, for fairly obvious reasons.)
930 Comments are indicated by the # character, and extend to the end of the line.
931 If you attempt to use /* */ C comments, it will be interpreted either as
932 division or pattern matching, depending on the context.
934 .Sh "Compound statements"
937 a sequence of commands may be treated as one command by enclosing it
939 We will call this a BLOCK.
941 The following compound commands may be used to control flow:
946 if (EXPR) BLOCK else BLOCK
947 if (EXPR) BLOCK elsif (EXPR) BLOCK .\|.\|. else BLOCK
948 LABEL while (EXPR) BLOCK
949 LABEL while (EXPR) BLOCK continue BLOCK
950 LABEL for (EXPR; EXPR; EXPR) BLOCK
951 LABEL foreach VAR (ARRAY) BLOCK
952 LABEL BLOCK continue BLOCK
955 Note that, unlike C and Pascal, these are defined in terms of BLOCKs, not
957 This means that the curly brackets are \fIrequired\fR\*(--no dangling statements allowed.
958 If you want to write conditionals without curly brackets there are several
960 The following all do the same thing:
964 if (!open(foo)) { die "Can't open $foo: $!"; }
965 die "Can't open $foo: $!" unless open(foo);
966 open(foo) || die "Can't open $foo: $!"; # foo or bust!
967 open(foo) ? \'hi mom\' : die "Can't open $foo: $!";
968 # a bit exotic, that last one
974 statement is straightforward.
975 Since BLOCKs are always bounded by curly brackets, there is never any
976 ambiguity about which
985 the sense of the test is reversed.
989 statement executes the block as long as the expression is true
990 (does not evaluate to the null string or 0).
991 The LABEL is optional, and if present, consists of an identifier followed by
993 The LABEL identifies the loop for the loop control statements
1001 BLOCK, it is always executed just before
1002 the conditional is about to be evaluated again, similarly to the third part
1006 Thus it can be used to increment a loop variable, even when the loop has
1007 been continued via the
1009 statement (similar to the C \*(L"continue\*(R" statement).
1013 is replaced by the word
1015 the sense of the test is reversed, but the conditional is still tested before
1016 the first iteration.
1022 statement, you may replace \*(L"(EXPR)\*(R" with a BLOCK, and the conditional
1023 is true if the value of the last command in that block is true.
1027 loop works exactly like the corresponding
1033 for ($i = 1; $i < 10; $i++) {
1047 The foreach loop iterates over a normal array value and sets the variable
1048 VAR to be each element of the array in turn.
1049 The \*(L"foreach\*(R" keyword is actually identical to the \*(L"for\*(R" keyword,
1050 so you can use \*(L"foreach\*(R" for readability or \*(L"for\*(R" for brevity.
1051 If VAR is omitted, $_ is set to each value.
1052 If ARRAY is an actual array (as opposed to an expression returning an array
1053 value), you can modify each element of the array
1054 by modifying VAR inside the loop.
1059 for (@ary) { s/foo/bar/; }
1061 foreach $elem (@elements) {
1066 for ((10,9,8,7,6,5,4,3,2,1,\'BOOM\')) {
1067 print $_, "\en"; sleep(1);
1070 for (1..15) { print "Merry Christmas\en"; }
1073 foreach $item (split(/:[\e\e\en:]*/, $ENV{\'TERMCAP\'}) {
1074 print "Item: $item\en";
1079 The BLOCK by itself (labeled or not) is equivalent to a loop that executes
1081 Thus you can use any of the loop control statements in it to leave or
1086 This construct is particularly nice for doing case structures.
1091 if (/^abc/) { $abc = 1; last foo; }
1092 if (/^def/) { $def = 1; last foo; }
1093 if (/^xyz/) { $xyz = 1; last foo; }
1098 There is no official switch statement in perl, because there
1099 are already several ways to write the equivalent.
1100 In addition to the above, you could write
1105 $abc = 1, last foo if /^abc/;
1106 $def = 1, last foo if /^def/;
1107 $xyz = 1, last foo if /^xyz/;
1115 /^abc/ && do { $abc = 1; last foo; }
1116 /^def/ && do { $def = 1; last foo; }
1117 /^xyz/ && do { $xyz = 1; last foo; }
1125 /^abc/ && ($abc = 1, last foo);
1126 /^def/ && ($def = 1, last foo);
1127 /^xyz/ && ($xyz = 1, last foo);
1144 As it happens, these are all optimized internally to a switch structure,
1145 so perl jumps directly to the desired statement, and you needn't worry
1146 about perl executing a lot of unnecessary statements when you have a string
1147 of 50 elsifs, as long as you are testing the same simple scalar variable
1148 using ==, eq, or pattern matching as above.
1149 (If you're curious as to whether the optimizer has done this for a particular
1150 case statement, you can use the \-D1024 switch to list the syntax tree
1152 .Sh "Simple statements"
1153 The only kind of simple statement is an expression evaluated for its side
1155 Every expression (simple statement) must be terminated with a semicolon.
1156 Note that this is like C, but unlike Pascal (and
1159 Any simple statement may optionally be followed by a
1160 single modifier, just before the terminating semicolon.
1161 The possible modifiers are:
1175 modifiers have the expected semantics.
1180 modifiers also have the expected semantics (conditional evaluated first),
1181 except when applied to a do-BLOCK command,
1182 in which case the block executes once before the conditional is evaluated.
1183 This is so that you can write loops like:
1190 } until $_ \|eq \|".\|\e\|n";
1195 operator below. Note also that the loop control commands described later will
1196 NOT work in this construct, since modifiers don't take loop labels.
1201 expressions work almost exactly like C expressions, only the differences
1202 will be mentioned here.
1208 The exponentiation operator.
1210 The exponentiation assignment operator.
1212 The null list, used to initialize an array to null.
1214 Concatenation of two strings.
1216 The concatenation assignment operator.
1218 String equality (== is numeric equality).
1219 For a mnemonic just think of \*(L"eq\*(R" as a string.
1220 (If you are used to the
1222 behavior of using == for either string or numeric equality
1223 based on the current form of the comparands, beware!
1224 You must be explicit here.)
1226 String inequality (!= is numeric inequality).
1230 String greater than.
1232 String less than or equal.
1234 String greater than or equal.
1236 Certain operations search or modify the string \*(L"$_\*(R" by default.
1237 This operator makes that kind of operation work on some other string.
1238 The right argument is a search pattern, substitution, or translation.
1239 The left argument is what is supposed to be searched, substituted, or
1240 translated instead of the default \*(L"$_\*(R".
1241 The return value indicates the success of the operation.
1242 (If the right argument is an expression other than a search pattern,
1243 substitution, or translation, it is interpreted as a search pattern
1245 This is less efficient than an explicit search, since the pattern must
1246 be compiled every time the expression is evaluated.)
1247 The precedence of this operator is lower than unary minus and autoincrement/decrement, but higher than everything else.
1249 Just like =~ except the return value is negated.
1251 The repetition operator.
1252 Returns a string consisting of the left operand repeated the
1253 number of times specified by the right operand.
1256 print \'\-\' x 80; # print row of dashes
1257 print \'\-\' x80; # illegal, x80 is identifier
1259 print "\et" x ($tab/8), \' \' x ($tab%8); # tab over
1263 The repetition assignment operator.
1265 The range operator, which is really two different operators depending
1267 In an array context, returns an array of values counting (by ones)
1268 from the left value to the right value.
1269 This is useful for writing \*(L"for (1..10)\*(R" loops and for doing
1270 slice operations on arrays.
1272 In a scalar context, .\|. returns a boolean value.
1273 The operator is bistable, like a flip-flop..
1274 Each .\|. operator maintains its own boolean state.
1275 It is false as long as its left operand is false.
1276 Once the left operand is true, the range operator stays true
1277 until the right operand is true,
1278 AFTER which the range operator becomes false again.
1279 (It doesn't become false till the next time the range operator is evaluated.
1280 It can become false on the same evaluation it became true, but it still returns
1282 The right operand is not evaluated while the operator is in the \*(L"false\*(R" state,
1283 and the left operand is not evaluated while the operator is in the \*(L"true\*(R" state.
1284 The scalar .\|. operator is primarily intended for doing line number ranges
1286 the fashion of \fIsed\fR or \fIawk\fR.
1287 The precedence is a little lower than || and &&.
1288 The value returned is either the null string for false, or a sequence number
1289 (beginning with 1) for true.
1290 The sequence number is reset for each range encountered.
1291 The final sequence number in a range has the string \'E0\' appended to it, which
1292 doesn't affect its numeric value, but gives you something to search for if you
1293 want to exclude the endpoint.
1294 You can exclude the beginning point by waiting for the sequence number to be
1296 If either operand of scalar .\|. is static, that operand is implicitly compared
1297 to the $. variable, the current line number.
1302 As a scalar operator:
1303 if (101 .\|. 200) { print; } # print 2nd hundred lines
1305 next line if (1 .\|. /^$/); # skip header lines
1307 s/^/> / if (/^$/ .\|. eof()); # quote body
1310 As an array operator:
1311 for (101 .\|. 200) { print; } # print $_ 100 times
1313 @foo = @foo[$[ .\|. $#foo]; # an expensive no-op
1314 @foo = @foo[$#foo-4 .\|. $#foo]; # slice last 5 items
1319 This unary operator takes one argument, either a filename or a filehandle,
1320 and tests the associated file to see if something is true about it.
1321 If the argument is omitted, tests $_, except for \-t, which tests
1323 It returns 1 for true and \'\' for false, or the undefined value if the
1325 Precedence is higher than logical and relational operators, but lower than
1326 arithmetic operators.
1327 The operator may be any of:
1329 \-r File is readable by effective uid.
1330 \-w File is writable by effective uid.
1331 \-x File is executable by effective uid.
1332 \-o File is owned by effective uid.
1333 \-R File is readable by real uid.
1334 \-W File is writable by real uid.
1335 \-X File is executable by real uid.
1336 \-O File is owned by real uid.
1338 \-z File has zero size.
1339 \-s File has non-zero size.
1340 \-f File is a plain file.
1341 \-d File is a directory.
1342 \-l File is a symbolic link.
1343 \-p File is a named pipe (FIFO).
1344 \-S File is a socket.
1345 \-b File is a block special file.
1346 \-c File is a character special file.
1347 \-u File has setuid bit set.
1348 \-g File has setgid bit set.
1349 \-k File has sticky bit set.
1350 \-t Filehandle is opened to a tty.
1351 \-T File is a text file.
1352 \-B File is a binary file (opposite of \-T).
1355 The interpretation of the file permission operators \-r, \-R, \-w, \-W, \-x and \-X
1356 is based solely on the mode of the file and the uids and gids of the user.
1357 There may be other reasons you can't actually read, write or execute the file.
1358 Also note that, for the superuser, \-r, \-R, \-w and \-W always return 1, and
1359 \-x and \-X return 1 if any execute bit is set in the mode.
1360 Scripts run by the superuser may thus need to do a stat() in order to determine
1361 the actual mode of the file, or temporarily set the uid to something else.
1369 next unless \-f $_; # ignore specials
1374 Note that \-s/a/b/ does not do a negated substitution.
1375 Saying \-exp($foo) still works as expected, however\*(--only single letters
1376 following a minus are interpreted as file tests.
1378 The \-T and \-B switches work as follows.
1379 The first block or so of the file is examined for odd characters such as
1380 strange control codes or metacharacters.
1381 If too many odd characters (>10%) are found, it's a \-B file, otherwise it's a \-T file.
1382 Also, any file containing null in the first block is considered a binary file.
1383 If \-T or \-B is used on a filehandle, the current stdio buffer is examined
1384 rather than the first block.
1385 Both \-T and \-B return TRUE on a null file, or a file at EOF when testing
1388 If any of the file tests (or either stat operator) are given the special
1389 filehandle consisting of a solitary underline, then the stat structure
1390 of the previous file test (or stat operator) is used, saving a system
1392 (This doesn't work with \-t, and you need to remember that lstat and -l
1393 will leave values in the stat structure for the symbolic link, not the
1398 print "Can do.\en" if -r $a || -w _ || -x _;
1402 print "Readable\en" if -r _;
1403 print "Writable\en" if -w _;
1404 print "Executable\en" if -x _;
1405 print "Setuid\en" if -u _;
1406 print "Setgid\en" if -g _;
1407 print "Sticky\en" if -k _;
1408 print "Text\en" if -T _;
1409 print "Binary\en" if -B _;
1413 Here is what C has that
1417 Address-of operator.
1419 Dereference-address operator.
1421 Type casting operator.
1425 does a certain amount of expression evaluation at compile time, whenever
1426 it determines that all of the arguments to an operator are static and have
1428 In particular, string concatenation happens at compile time between literals that don't do variable substitution.
1429 Backslash interpretation also happens at compile time.
1434 \'Now is the time for all\' . "\|\e\|n" .
1435 \'good men to come to.\'
1438 and this all reduces to one string internally.
1440 The autoincrement operator has a little extra built-in magic to it.
1441 If you increment a variable that is numeric, or that has ever been used in
1442 a numeric context, you get a normal increment.
1443 If, however, the variable has only been used in string contexts since it
1444 was set, and has a value that is not null and matches the
1445 pattern /^[a\-zA\-Z]*[0\-9]*$/, the increment is done
1446 as a string, preserving each character within its range, with carry:
1449 print ++($foo = \'99\'); # prints \*(L'100\*(R'
1450 print ++($foo = \'a0\'); # prints \*(L'a1\*(R'
1451 print ++($foo = \'Az\'); # prints \*(L'Ba\*(R'
1452 print ++($foo = \'zz\'); # prints \*(L'aaa\*(R'
1455 The autodecrement is not magical.
1457 The range operator (in an array context) makes use of the magical
1458 autoincrement algorithm if the minimum and maximum are strings.
1461 @alphabet = (\'A\' .. \'Z\');
1463 to get all the letters of the alphabet, or
1465 $hexdigit = (0 .. 9, \'a\' .. \'f\')[$num & 15];
1467 to get a hexadecimal digit, or
1469 @z2 = (\'01\' .. \'31\'); print @z2[$mday];
1471 to get dates with leading zeros.
1472 (If the final value specified is not in the sequence that the magical increment
1473 would produce, the sequence goes until the next value would be longer than
1474 the final value specified.)