2 ''' $Header: perl.man.1,v 3.0.1.1 89/11/11 04:41:22 lwall Locked $
4 ''' $Log: perl.man.1,v $
5 ''' Revision 3.0.1.1 89/11/11 04:41:22 lwall
6 ''' patch2: explained about sh and ${1+"$@"}
7 ''' patch2: documented that space must separate word and '' string
9 ''' Revision 3.0 89/10/18 15:21:29 lwall
31 ''' Set up \*(-- to give an unbreakable dash;
32 ''' string Tr holds user defined translation string.
33 ''' Bell System Logo is used as a dummy character.
38 .if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
39 .if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
56 perl \- Practical Extraction and Report Language
59 [options] filename args
62 is an interpreted language optimized for scanning arbitrary text files,
63 extracting information from those text files, and printing reports based
65 It's also a good language for many system management tasks.
66 The language is intended to be practical (easy to use, efficient, complete)
67 rather than beautiful (tiny, elegant, minimal).
68 It combines (in the author's opinion, anyway) some of the best features of C,
69 \fIsed\fR, \fIawk\fR, and \fIsh\fR,
70 so people familiar with those languages should have little difficulty with it.
71 (Language historians will also note some vestiges of \fIcsh\fR, Pascal, and
73 Expression syntax corresponds quite closely to C expression syntax.
74 Unlike most Unix utilities,
76 does not arbitrarily limit the size of your data\*(--if you've got
79 can slurp in your whole file as a single string.
80 Recursion is of unlimited depth.
81 And the hash tables used by associative arrays grow as necessary to prevent
84 uses sophisticated pattern matching techniques to scan large amounts of
86 Although optimized for scanning text,
88 can also deal with binary data, and can make dbm files look like associative
89 arrays (where dbm is available).
92 scripts are safer than C programs
93 through a dataflow tracing mechanism which prevents many stupid security holes.
94 If you have a problem that would ordinarily use \fIsed\fR
95 or \fIawk\fR or \fIsh\fR, but it
96 exceeds their capabilities or must run a little faster,
97 and you don't want to write the silly thing in C, then
100 There are also translators to turn your
111 looks for your script in one of the following places:
113 Specified line by line via
115 switches on the command line.
117 Contained in the file specified by the first filename on the command line.
118 (Note that systems supporting the #! notation invoke interpreters this way.)
120 Passed in implicitly via standard input.
121 This only works if there are no filename arguments\*(--to pass
124 script you must explicitly specify a \- for the script name.
126 After locating your script,
128 compiles it to an internal form.
129 If the script is syntactically correct, it is executed.
131 Note: on first reading this section may not make much sense to you. It's here
132 at the front for easy reference.
134 A single-character option may be combined with the following option, if any.
135 This is particularly useful when invoking a script using the #! construct which
136 only allows one argument. Example:
140 #!/usr/bin/perl \-spi.bak # same as \-s \-p \-i.bak
147 turns on autosplit mode when used with a
151 An implicit split command to the @F array
152 is done as the first thing inside the implicit while loop produced by
159 perl \-ane \'print pop(@F), "\en";\'
165 print pop(@F), "\en";
171 runs the script under the perl debugger.
172 See the section on Debugging.
175 sets debugging flags.
176 To watch how it executes your script, use
178 (This only works if debugging is compiled into your
180 Another nice value is \-D1024, which lists your compiled syntax tree.
181 And \-D512 displays compiled regular expressions.
183 .BI \-e " commandline"
184 may be used to enter one line of script.
187 commands may be given to build up a multi-line script.
192 will not look for a script filename in the argument list.
195 specifies that files processed by the <> construct are to be edited
197 It does this by renaming the input file, opening the output file by the
198 same name, and selecting that output file as the default for print statements.
199 The extension, if supplied, is added to the name of the
200 old file to make a backup copy.
201 If no extension is supplied, no backup is made.
202 Saying \*(L"perl \-p \-i.bak \-e "s/foo/bar/;" .\|.\|. \*(R" is the same as using
207 #!/usr/bin/perl \-pi.bak
210 which is equivalent to
215 if ($ARGV ne $oldargv) {
216 rename($ARGV, $ARGV . \'.bak\');
217 open(ARGVOUT, ">$ARGV");
224 print; # this prints to original filename
231 form doesn't need to compare $ARGV to $oldargv to know when
232 the filename has changed.
233 It does, however, use ARGVOUT for the selected filehandle.
236 is restored as the default output filehandle after the loop.
238 You can use eof to locate the end of each input file, in case you want
239 to append to each file, or reset line numbering (see example under eof).
242 may be used in conjunction with
244 to tell the C preprocessor where to look for include files.
245 By default /usr/include and /usr/lib/perl are searched.
250 to assume the following loop around your script, which makes it iterate
251 over filename arguments somewhat like \*(L"sed \-n\*(R" or \fIawk\fR:
256 .\|.\|. # your script goes here
260 Note that the lines are not printed by default.
263 to have lines printed.
264 Here is an efficient way to delete all files older than a week:
267 find . \-mtime +7 \-print | perl \-ne \'chop;unlink;\'
270 This is faster than using the \-exec switch of find because you don't have to
271 start a process on every filename found.
276 to assume the following loop around your script, which makes it iterate
277 over filename arguments somewhat like \fIsed\fR:
282 .\|.\|. # your script goes here
288 Note that the lines are printed automatically.
289 To suppress printing use the
299 causes your script to be run through the C preprocessor before
302 (Since both comments and cpp directives begin with the # character,
303 you should avoid starting comments with any words recognized
304 by the C preprocessor such as \*(L"if\*(R", \*(L"else\*(R" or \*(L"define\*(R".)
307 enables some rudimentary switch parsing for switches on the command line
308 after the script name but before any filename arguments (or before a \-\|\-).
309 Any switch found there is removed from @ARGV and sets the corresponding variable in the
312 The following script prints \*(L"true\*(R" if and only if the script is
313 invoked with a \-xyz switch.
318 if ($xyz) { print "true\en"; }
325 use the PATH environment variable to search for the script
326 (unless the name of the script starts with a slash).
327 Typically this is used to emulate #! startup on machines that don't
328 support #!, in the following manner:
332 eval "exec /usr/bin/perl \-S $0 $*"
333 if $running_under_some_shell;
336 The system ignores the first line and feeds the script to /bin/sh,
337 which proceeds to try to execute the
339 script as a shell script.
340 The shell executes the second line as a normal shell command, and thus
344 On some systems $0 doesn't always contain the full pathname,
349 to search for the script if necessary.
352 locates the script, it parses the lines and ignores them because
353 the variable $running_under_some_shell is never true.
354 A better construct than $* would be ${1+"$@"}, which handles embedded spaces
355 and such in the filenames, but doesn't work if the script is being interpreted
357 In order to start up sh rather than csh, some systems may have to replace the
358 #! line with a line containing just
359 a colon, which will be politely ignored by perl.
364 to dump core after compiling your script.
365 You can then take this core dump and turn it into an executable file
366 by using the undump program (not supplied).
367 This speeds startup at the expense of some disk space (which you can
368 minimize by stripping the executable).
369 (Still, a "hello world" executable comes out to about 200K on my machine.)
370 If you are going to run your executable as a set-id program then you
371 should probably compile it using taintperl rather than normal perl.
372 If you want to execute a portion of your script before dumping, use the
373 dump operator instead.
378 to do unsafe operations.
379 Currently the only \*(L"unsafe\*(R" operation is the unlinking of directories while
380 running as superuser.
383 prints the version and patchlevel of your
388 prints warnings about identifiers that are mentioned only once, and scalar
389 variables that are used before being set.
390 Also warns about redefined subroutines, and references to undefined
391 filehandles or filehandles opened readonly that you are attempting to
393 Also warns you if you use == on values that don't look like numbers, and if
394 your subroutines recurse more than 100 deep.
395 .Sh "Data Types and Objects"
398 has three data types: scalars, arrays of scalars, and
399 associative arrays of scalars.
400 Normal arrays are indexed by number, and associative arrays by string.
402 The interpretation of operations and values in perl sometimes
403 depends on the requirements
404 of the context around the operation or value.
405 There are three major contexts: string, numeric and array.
406 Certain operations return array values
407 in contexts wanting an array, and scalar values otherwise.
408 (If this is true of an operation it will be mentioned in the documentation
410 Operations which return scalars don't care whether the context is looking
411 for a string or a number, but
412 scalar variables and values are interpreted as strings or numbers
413 as appropriate to the context.
414 A scalar is interpreted as TRUE in the boolean sense if it is not the null
416 Booleans returned by operators are 1 for true and \'0\' or \'\' (the null
419 There are actually two varieties of null string: defined and undefined.
420 Undefined null strings are returned when there is no real value for something,
421 such as when there was an error, or at end of file, or when you refer
422 to an uninitialized variable or element of an array.
423 An undefined null string may become defined the first time you access it, but
424 prior to that you can use the defined() operator to determine whether the
425 value is defined or not.
427 References to scalar variables always begin with \*(L'$\*(R', even when referring
428 to a scalar that is part of an array.
433 $days \h'|2i'# a simple scalar variable
434 $days[28] \h'|2i'# 29th element of array @days
435 $days{\'Feb\'}\h'|2i'# one value from an associative array
436 $#days \h'|2i'# last index of array @days
438 but entire arrays or array slices are denoted by \*(L'@\*(R':
440 @days \h'|2i'# ($days[0], $days[1],\|.\|.\|. $days[n])
441 @days[3,4,5]\h'|2i'# same as @days[3.\|.5]
442 @days{'a','c'}\h'|2i'# same as ($days{'a'},$days{'c'})
444 and entire associative arrays are denoted by \*(L'%\*(R':
446 %days \h'|2i'# (key1, val1, key2, val2 .\|.\|.)
449 Any of these eight constructs may serve as an lvalue,
450 that is, may be assigned to.
451 (It also turns out that an assignment is itself an lvalue in
452 certain contexts\*(--see examples under s, tr and chop.)
453 Assignment to a scalar evaluates the righthand side in a scalar context,
454 while assignment to an array or array slice evaluates the righthand side
457 You may find the length of array @days by evaluating
458 \*(L"$#days\*(R", as in
460 (Actually, it's not the length of the array, it's the subscript of the last element, since there is (ordinarily) a 0th element.)
461 Assigning to $#days changes the length of the array.
462 Shortening an array by this method does not actually destroy any values.
463 Lengthening an array that was previously shortened recovers the values that
464 were in those elements.
465 You can also gain some measure of efficiency by preextending an array that
467 (You can also extend an array by assigning to an element that is off the
469 This differs from assigning to $#whatever in that intervening values
470 are set to null rather than recovered.)
471 You can truncate an array down to nothing by assigning the null list () to
473 The following are exactly equivalent
477 $#whatever = $[ \- 1;
481 Multi-dimensional arrays are not directly supported, but see the discussion
482 of the $; variable later for a means of emulating multiple subscripts with
483 an associative array.
485 Every data type has its own namespace.
486 You can, without fear of conflict, use the same name for a scalar variable,
487 an array, an associative array, a filehandle, a subroutine name, and/or
489 Since variable and array references always start with \*(L'$\*(R', \*(L'@\*(R',
490 or \*(L'%\*(R', the \*(L"reserved\*(R" words aren't in fact reserved
491 with respect to variable names.
492 (They ARE reserved with respect to labels and filehandles, however, which
493 don't have an initial special character.
494 Hint: you could say open(LOG,\'logfile\') rather than open(log,\'logfile\').
495 Using uppercase filehandles also improves readability and protects you
496 from conflict with future reserved words.)
497 Case IS significant\*(--\*(L"FOO\*(R", \*(L"Foo\*(R" and \*(L"foo\*(R" are all
499 Names which start with a letter may also contain digits and underscores.
500 Names which do not start with a letter are limited to one character,
501 e.g. \*(L"$%\*(R" or \*(L"$$\*(R".
502 (Most of the one character names have a predefined significance to
506 Numeric literals are specified in any of the usual floating point or
518 String literals are delimited by either single or double quotes.
519 They work much like shell quotes:
520 double-quoted string literals are subject to backslash and variable
521 substitution; single-quoted strings are not (except for \e\' and \e\e).
522 The usual backslash rules apply for making characters such as newline, tab, etc.
523 You can also embed newlines directly in your strings, i.e. they can end on
524 a different line than they begin.
525 This is nice, but if you forget your trailing quote, the error will not be
528 finds another line containing the quote character, which
529 may be much further on in the script.
530 Variable substitution inside strings is limited to scalar variables, normal
531 array values, and array slices.
532 (In other words, identifiers beginning with $ or @, followed by an optional
533 bracketed expression as a subscript.)
534 The following code segment prints out \*(L"The price is $100.\*(R"
538 $Price = \'$100\';\h'|3.5i'# not interpreted
539 print "The price is $Price.\e\|n";\h'|3.5i'# interpreted
542 Note that you can put curly brackets around the identifier to delimit it
543 from following alphanumerics.
544 Also note that a single quoted string must be separated from a preceding
545 word by a space, since single quote is a valid character in an identifier
548 Array values are interpolated into double-quoted strings by joining all the
549 elements of the array with the delimiter specified in the $" variable,
551 (Since in versions of perl prior to 3.0 the @ character was not a metacharacter
552 in double-quoted strings, the interpolation of @array, $array[EXPR],
553 @array[LIST], $array{EXPR}, or @array{LIST} only happens if array is
554 referenced elsewhere in the program or is predefined.)
555 The following are equivalent:
559 $temp = join($",@ARGV);
565 Within search patterns (which also undergo double-quotish substitution)
566 there is a bad ambiguity: Is /$foo[bar]/ to be
567 interpreted as /${foo}[bar]/ (where [bar] is a character class for the
568 regular expression) or as /${foo[bar]}/ (where [bar] is the subscript to
570 If @foo doesn't otherwise exist, then it's obviously a character class.
571 If @foo exists, perl takes a good guess about [bar], and is almost always right.
572 If it does guess wrong, or if you're just plain paranoid,
573 you can force the correct interpretation with curly brackets as above.
575 A line-oriented form of quoting is based on the shell here-is syntax.
576 Following a << you specify a string to terminate the quoted material, and all lines
577 following the current line down to the terminating string are the value
579 The terminating string may be either an identifier (a word), or some
581 If quoted, the type of quotes you use determines the treatment of the text,
582 just as in regular quoting.
583 An unquoted identifier works like double quotes.
584 There must be no space between the << and the identifier.
585 (If you put a space it will be treated as a null identifier, which is
586 valid, and matches the first blank line\*(--see Merry Christmas example below.)
587 The terminating string must appear by itself (unquoted and with no surrounding
588 whitespace) on the terminating line.
591 print <<EOF; # same as above
595 print <<"EOF"; # same as above
599 print << x 10; # null identifier is delimiter
602 print <<`EOC`; # execute commands
607 print <<foo, <<bar; # you can stack them
614 Array literals are denoted by separating individual values by commas, and
615 enclosing the list in parentheses.
616 In a context not requiring an array value, the value of the array literal
617 is the value of the final element, as in the C comma operator.
622 @foo = (\'cc\', \'\-E\', $bar);
624 assigns the entire array value to array foo, but
626 $foo = (\'cc\', \'\-E\', $bar);
629 assigns the value of variable bar to variable foo.
630 Array lists may be assigned to if and only if each element of the list
634 ($a, $b, $c) = (1, 2, 3);
636 ($map{\'red\'}, $map{\'blue\'}, $map{\'green\'}) = (0x00f, 0x0f0, 0xf00);
638 The final element may be an array or an associative array:
640 ($a, $b, @rest) = split;
641 local($a, $b, %rest) = @_;
644 You can actually put an array anywhere in the list, but the first array
645 in the list will soak up all the values, and anything after it will get
647 This may be useful in a local().
649 An associative array literal contains pairs of values to be interpreted
650 as a key and a value:
654 # same as map assignment above
655 %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
658 Array assignment in a scalar context returns the number of elements
659 produced by the expression on the right side of the assignment:
662 $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
666 There are several other pseudo-literals that you should know about.
667 If a string is enclosed by backticks (grave accents), it first undergoes
668 variable substitution just like a double quoted string.
669 It is then interpreted as a command, and the output of that command
670 is the value of the pseudo-literal, like in a shell.
671 The command is executed each time the pseudo-literal is evaluated.
672 The status value of the command is returned in $? (see Predefined Names
673 for the interpretation of $?).
674 Unlike in \f2csh\f1, no translation is done on the return
675 data\*(--newlines remain newlines.
676 Unlike in any of the shells, single quotes do not hide variable names
677 in the command from interpretation.
678 To pass a $ through to the shell you need to hide it with a backslash.
680 Evaluating a filehandle in angle brackets yields the next line
681 from that file (newline included, so it's never false until EOF, at
682 which time an undefined value is returned).
683 Ordinarily you must assign that value to a variable,
684 but there is one situation where in which an automatic assignment happens.
685 If (and only if) the input symbol is the only thing inside the conditional of a
688 automatically assigned to the variable \*(L"$_\*(R".
689 (This may seem like an odd thing to you, but you'll use the construct
693 Anyway, the following lines are equivalent to each other:
697 while ($_ = <STDIN>) { print; }
698 while (<STDIN>) { print; }
699 for (\|;\|<STDIN>;\|) { print; }
700 print while $_ = <STDIN>;
715 will also work except in packages, where they would be interpreted as
716 local identifiers rather than global.)
717 Additional filehandles may be created with the
721 If a <FILEHANDLE> is used in a context that is looking for an array, an array
722 consisting of all the input lines is returned, one line per array element.
723 It's easy to make a LARGE data space this way, so use with care.
725 The null filehandle <> is special and can be used to emulate the behavior of
726 \fIsed\fR and \fIawk\fR.
727 Input from <> comes either from standard input, or from each file listed on
729 Here's how it works: the first time <> is evaluated, the ARGV array is checked,
730 and if it is null, $ARGV[0] is set to \'-\', which when opened gives you standard
732 The ARGV array is then processed as a list of filenames.
738 .\|.\|. # code for each line
744 unshift(@ARGV, \'\-\') \|if \|$#ARGV < $[;
745 while ($ARGV = shift) {
748 .\|.\|. # code for each line
753 except that it isn't as cumbersome to say.
754 It really does shift array ARGV and put the current filename into
756 It also uses filehandle ARGV internally.
757 You can modify @ARGV before the first <> as long as you leave the first
758 filename at the beginning of the array.
759 Line numbers ($.) continue as if the input was one big happy file.
760 (But see example under eof for how to reset line numbers on each file.)
763 If you want to set @ARGV to your own list of files, go right ahead.
764 If you want to pass switches into your script, you can
765 put a loop on the front like this:
769 while ($_ = $ARGV[0], /\|^\-/\|) {
771 last if /\|^\-\|\-$\|/\|;
772 /\|^\-D\|(.*\|)/ \|&& \|($debug = $1);
773 /\|^\-v\|/ \|&& \|$verbose++;
774 .\|.\|. # other switches
777 .\|.\|. # code for each line
781 The <> symbol will return FALSE only once.
782 If you call it again after this it will assume you are processing another
783 @ARGV list, and if you haven't set @ARGV, will input from
786 If the string inside the angle brackets is a reference to a scalar variable
788 then that variable contains the name of the filehandle to input from.
790 If the string inside angle brackets is not a filehandle, it is interpreted
791 as a filename pattern to be globbed, and either an array of filenames or the
792 next filename in the list is returned, depending on context.
793 One level of $ interpretation is done first, but you can't say <$foo>
794 because that's an indirect filehandle as explained in the previous
796 You could insert curly brackets to force interpretation as a
797 filename glob: <${foo}>.
809 open(foo, "echo *.c | tr \-s \' \et\er\ef\' \'\e\e012\e\e012\e\e012\e\e012\'|");
816 In fact, it's currently implemented that way.
817 (Which means it will not work on filenames with spaces in them unless
818 you have /bin/csh on your machine.)
819 Of course, the shortest way to do the above is:
829 script consists of a sequence of declarations and commands.
830 The only things that need to be declared in
832 are report formats and subroutines.
833 See the sections below for more information on those declarations.
834 All uninitialized objects user-created objects are assumed to
835 start with a null or 0 value until they
836 are defined by some explicit operation such as assignment.
837 The sequence of commands is executed just once, unlike in
841 scripts, where the sequence of commands is executed for each input line.
842 While this means that you must explicitly loop over the lines of your input file
843 (or files), it also means you have much more control over which files and which
845 (Actually, I'm lying\*(--it is possible to do an implicit loop with either the
851 A declaration can be put anywhere a command can, but has no effect on the
852 execution of the primary sequence of commands--declarations all take effect
854 Typically all the declarations are put at the beginning or the end of the script.
857 is, for the most part, a free-form language.
858 (The only exception to this is format declarations, for fairly obvious reasons.)
859 Comments are indicated by the # character, and extend to the end of the line.
860 If you attempt to use /* */ C comments, it will be interpreted either as
861 division or pattern matching, depending on the context.
863 .Sh "Compound statements"
866 a sequence of commands may be treated as one command by enclosing it
868 We will call this a BLOCK.
870 The following compound commands may be used to control flow:
875 if (EXPR) BLOCK else BLOCK
876 if (EXPR) BLOCK elsif (EXPR) BLOCK .\|.\|. else BLOCK
877 LABEL while (EXPR) BLOCK
878 LABEL while (EXPR) BLOCK continue BLOCK
879 LABEL for (EXPR; EXPR; EXPR) BLOCK
880 LABEL foreach VAR (ARRAY) BLOCK
881 LABEL BLOCK continue BLOCK
884 Note that, unlike C and Pascal, these are defined in terms of BLOCKs, not
886 This means that the curly brackets are \fIrequired\fR\*(--no dangling statements allowed.
887 If you want to write conditionals without curly brackets there are several
889 The following all do the same thing:
893 if (!open(foo)) { die "Can't open $foo: $!"; }
894 die "Can't open $foo: $!" unless open(foo);
895 open(foo) || die "Can't open $foo: $!"; # foo or bust!
896 open(foo) ? die "Can't open $foo: $!" : \'hi mom\';
897 # a bit exotic, that last one
903 statement is straightforward.
904 Since BLOCKs are always bounded by curly brackets, there is never any
905 ambiguity about which
914 the sense of the test is reversed.
918 statement executes the block as long as the expression is true
919 (does not evaluate to the null string or 0).
920 The LABEL is optional, and if present, consists of an identifier followed by
922 The LABEL identifies the loop for the loop control statements
930 BLOCK, it is always executed just before
931 the conditional is about to be evaluated again, similarly to the third part
935 Thus it can be used to increment a loop variable, even when the loop has
936 been continued via the
938 statement (similar to the C \*(L"continue\*(R" statement).
942 is replaced by the word
944 the sense of the test is reversed, but the conditional is still tested before
951 statement, you may replace \*(L"(EXPR)\*(R" with a BLOCK, and the conditional
952 is true if the value of the last command in that block is true.
956 loop works exactly like the corresponding
962 for ($i = 1; $i < 10; $i++) {
976 The foreach loop iterates over a normal array value and sets the variable
977 VAR to be each element of the array in turn.
978 The \*(L"foreach\*(R" keyword is actually identical to the \*(L"for\*(R" keyword,
979 so you can use \*(L"foreach\*(R" for readability or \*(L"for\*(R" for brevity.
980 If VAR is omitted, $_ is set to each value.
981 If ARRAY is an actual array (as opposed to an expression returning an array
982 value), you can modify each element of the array
983 by modifying VAR inside the loop.
988 for (@ary) { s/foo/bar/; }
990 foreach $elem (@elements) {
995 for ((10,9,8,7,6,5,4,3,2,1,\'BOOM\')) {
996 print $_, "\en"; sleep(1);
999 for (1..15) { print "Merry Christmas\en"; }
1002 foreach $item (split(/:[\e\e\en:]*/, $ENV{\'TERMCAP\'}) {
1003 print "Item: $item\en";
1008 The BLOCK by itself (labeled or not) is equivalent to a loop that executes
1010 Thus you can use any of the loop control statements in it to leave or
1015 This construct is particularly nice for doing case structures.
1020 if (/^abc/) { $abc = 1; last foo; }
1021 if (/^def/) { $def = 1; last foo; }
1022 if (/^xyz/) { $xyz = 1; last foo; }
1027 There is no official switch statement in perl, because there
1028 are already several ways to write the equivalent.
1029 In addition to the above, you could write
1034 $abc = 1, last foo if /^abc/;
1035 $def = 1, last foo if /^def/;
1036 $xyz = 1, last foo if /^xyz/;
1044 /^abc/ && do { $abc = 1; last foo; }
1045 /^def/ && do { $def = 1; last foo; }
1046 /^xyz/ && do { $xyz = 1; last foo; }
1054 /^abc/ && ($abc = 1, last foo);
1055 /^def/ && ($def = 1, last foo);
1056 /^xyz/ && ($xyz = 1, last foo);
1064 { $abc = 1; last foo; }
1066 { $def = 1; last foo; }
1068 { $xyz = 1; last foo; }
1073 As it happens, these are all optimized internally to a switch structure,
1074 so perl jumps directly to the desired statement, and you needn't worry
1075 about perl executing a lot of unnecessary statements when you have a string
1076 of 50 elsifs, as long as you are testing the same simple scalar variable
1077 using ==, eq, or pattern matching as above.
1078 (If you're curious as to whether the optimizer has done this for a particular
1079 case statement, you can use the \-D1024 switch to list the syntax tree
1081 .Sh "Simple statements"
1082 The only kind of simple statement is an expression evaluated for its side
1084 Every expression (simple statement) must be terminated with a semicolon.
1085 Note that this is like C, but unlike Pascal (and
1088 Any simple statement may optionally be followed by a
1089 single modifier, just before the terminating semicolon.
1090 The possible modifiers are:
1104 modifiers have the expected semantics.
1109 modifiers also have the expected semantics (conditional evaluated first),
1110 except when applied to a do-BLOCK command,
1111 in which case the block executes once before the conditional is evaluated.
1112 This is so that you can write loops like:
1119 } until $_ \|eq \|".\|\e\|n";
1124 operator below. Note also that the loop control commands described later will
1125 NOT work in this construct, since modifiers don't take loop labels.
1130 expressions work almost exactly like C expressions, only the differences
1131 will be mentioned here.
1137 The exponentiation operator.
1139 The exponentiation assignment operator.
1141 The null list, used to initialize an array to null.
1143 Concatenation of two strings.
1145 The concatenation assignment operator.
1147 String equality (== is numeric equality).
1148 For a mnemonic just think of \*(L"eq\*(R" as a string.
1149 (If you are used to the
1151 behavior of using == for either string or numeric equality
1152 based on the current form of the comparands, beware!
1153 You must be explicit here.)
1155 String inequality (!= is numeric inequality).
1159 String greater than.
1161 String less than or equal.
1163 String greater than or equal.
1165 Certain operations search or modify the string \*(L"$_\*(R" by default.
1166 This operator makes that kind of operation work on some other string.
1167 The right argument is a search pattern, substitution, or translation.
1168 The left argument is what is supposed to be searched, substituted, or
1169 translated instead of the default \*(L"$_\*(R".
1170 The return value indicates the success of the operation.
1171 (If the right argument is an expression other than a search pattern,
1172 substitution, or translation, it is interpreted as a search pattern
1174 This is less efficient than an explicit search, since the pattern must
1175 be compiled every time the expression is evaluated.)
1176 The precedence of this operator is lower than unary minus and autoincrement/decrement, but higher than everything else.
1178 Just like =~ except the return value is negated.
1180 The repetition operator.
1181 Returns a string consisting of the left operand repeated the
1182 number of times specified by the right operand.
1185 print \'\-\' x 80; # print row of dashes
1186 print \'\-\' x80; # illegal, x80 is identifier
1188 print "\et" x ($tab/8), \' \' x ($tab%8); # tab over
1192 The repetition assignment operator.
1194 The range operator, which is really two different operators depending
1196 In an array context, returns an array of values counting (by ones)
1197 from the left value to the right value.
1198 This is useful for writing \*(L"for (1..10)\*(R" loops and for doing
1199 slice operations on arrays.
1201 In a scalar context, .\|. returns a boolean value.
1202 The operator is bistable, like a flip-flop..
1203 Each .\|. operator maintains its own boolean state.
1204 It is false as long as its left operand is false.
1205 Once the left operand is true, the range operator stays true
1206 until the right operand is true,
1207 AFTER which the range operator becomes false again.
1208 (It doesn't become false till the next time the range operator is evaluated.
1209 It can become false on the same evaluation it became true, but it still returns
1211 The right operand is not evaluated while the operator is in the \*(L"false\*(R" state,
1212 and the left operand is not evaluated while the operator is in the \*(L"true\*(R" state.
1213 The scalar .\|. operator is primarily intended for doing line number ranges
1215 the fashion of \fIsed\fR or \fIawk\fR.
1216 The precedence is a little lower than || and &&.
1217 The value returned is either the null string for false, or a sequence number
1218 (beginning with 1) for true.
1219 The sequence number is reset for each range encountered.
1220 The final sequence number in a range has the string \'E0\' appended to it, which
1221 doesn't affect its numeric value, but gives you something to search for if you
1222 want to exclude the endpoint.
1223 You can exclude the beginning point by waiting for the sequence number to be
1225 If either operand of scalar .\|. is static, that operand is implicitly compared
1226 to the $. variable, the current line number.
1231 As a scalar operator:
1232 if (101 .\|. 200) { print; } # print 2nd hundred lines
1234 next line if (1 .\|. /^$/); # skip header lines
1236 s/^/> / if (/^$/ .\|. eof()); # quote body
1239 As an array operator:
1240 for (101 .\|. 200) { print; } # print $_ 100 times
1242 @foo = @foo[$[ .\|. $#foo]; # an expensive no-op
1243 @foo = @foo[$#foo-4 .\|. $#foo]; # slice last 5 items
1248 This unary operator takes one argument, either a filename or a filehandle,
1249 and tests the associated file to see if something is true about it.
1250 If the argument is omitted, tests $_, except for \-t, which tests
1252 It returns 1 for true and \'\' for false, or the undefined value if the
1254 Precedence is higher than logical and relational operators, but lower than
1255 arithmetic operators.
1256 The operator may be any of:
1258 \-r File is readable by effective uid.
1259 \-w File is writable by effective uid.
1260 \-x File is executable by effective uid.
1261 \-o File is owned by effective uid.
1262 \-R File is readable by real uid.
1263 \-W File is writable by real uid.
1264 \-X File is executable by real uid.
1265 \-O File is owned by real uid.
1267 \-z File has zero size.
1268 \-s File has non-zero size.
1269 \-f File is a plain file.
1270 \-d File is a directory.
1271 \-l File is a symbolic link.
1272 \-p File is a named pipe (FIFO).
1273 \-S File is a socket.
1274 \-b File is a block special file.
1275 \-c File is a character special file.
1276 \-u File has setuid bit set.
1277 \-g File has setgid bit set.
1278 \-k File has sticky bit set.
1279 \-t Filehandle is opened to a tty.
1280 \-T File is a text file.
1281 \-B File is a binary file (opposite of \-T).
1284 The interpretation of the file permission operators \-r, \-R, \-w, \-W, \-x and \-X
1285 is based solely on the mode of the file and the uids and gids of the user.
1286 There may be other reasons you can't actually read, write or execute the file.
1287 Also note that, for the superuser, \-r, \-R, \-w and \-W always return 1, and
1288 \-x and \-X return 1 if any execute bit is set in the mode.
1289 Scripts run by the superuser may thus need to do a stat() in order to determine
1290 the actual mode of the file, or temporarily set the uid to something else.
1298 next unless \-f $_; # ignore specials
1303 Note that \-s/a/b/ does not do a negated substitution.
1304 Saying \-exp($foo) still works as expected, however\*(--only single letters
1305 following a minus are interpreted as file tests.
1307 The \-T and \-B switches work as follows.
1308 The first block or so of the file is examined for odd characters such as
1309 strange control codes or metacharacters.
1310 If too many odd characters (>10%) are found, it's a \-B file, otherwise it's a \-T file.
1311 Also, any file containing null in the first block is considered a binary file.
1312 If \-T or \-B is used on a filehandle, the current stdio buffer is examined
1313 rather than the first block.
1314 Both \-T and \-B return TRUE on a null file, or a file at EOF when testing
1317 If any of the file tests (or either stat operator) are given the special
1318 filehandle consisting of a solitary underline, then the stat structure
1319 of the previous file test (or stat operator) is used, saving a system
1321 (This doesn't work with \-t, and you need to remember that lstat and -l
1322 will leave values in the stat structure for the symbolic link, not the
1327 print "Can do.\en" if -r $a || -w _ || -x _;
1331 print "Readable\en" if -r _;
1332 print "Writable\en" if -w _;
1333 print "Executable\en" if -x _;
1334 print "Setuid\en" if -u _;
1335 print "Setgid\en" if -g _;
1336 print "Sticky\en" if -k _;
1337 print "Text\en" if -T _;
1338 print "Binary\en" if -B _;
1342 Here is what C has that
1346 Address-of operator.
1348 Dereference-address operator.
1350 Type casting operator.
1354 does a certain amount of expression evaluation at compile time, whenever
1355 it determines that all of the arguments to an operator are static and have
1357 In particular, string concatenation happens at compile time between literals that don't do variable substitution.
1358 Backslash interpretation also happens at compile time.
1363 \'Now is the time for all\' . "\|\e\|n" .
1364 \'good men to come to.\'
1367 and this all reduces to one string internally.
1369 The autoincrement operator has a little extra built-in magic to it.
1370 If you increment a variable that is numeric, or that has ever been used in
1371 a numeric context, you get a normal increment.
1372 If, however, the variable has only been used in string contexts since it
1373 was set, and has a value that is not null and matches the
1374 pattern /^[a\-zA\-Z]*[0\-9]*$/, the increment is done
1375 as a string, preserving each character within its range, with carry:
1378 print ++($foo = \'99\'); # prints \*(L'100\*(R'
1379 print ++($foo = \'a0\'); # prints \*(L'a1\*(R'
1380 print ++($foo = \'Az\'); # prints \*(L'Ba\*(R'
1381 print ++($foo = \'zz\'); # prints \*(L'aaa\*(R'
1384 The autodecrement is not magical.