2 ''' $Header: perl_man.1,v 3.0.1.10 90/11/10 01:45:16 lwall Locked $
4 ''' $Log: perl.man.1,v $
5 ''' Revision 3.0.1.10 90/11/10 01:45:16 lwall
6 ''' patch38: random cleanup
8 ''' Revision 3.0.1.9 90/10/20 02:14:24 lwall
9 ''' patch37: fixed various typos in man page
11 ''' Revision 3.0.1.8 90/10/15 18:16:19 lwall
12 ''' patch29: added DATA filehandle to read stuff after __END__
13 ''' patch29: added cmp and <=>
14 ''' patch29: added -M, -A and -C
16 ''' Revision 3.0.1.7 90/08/09 04:24:03 lwall
17 ''' patch19: added -x switch to extract script from input trash
18 ''' patch19: Added -c switch to do compilation only
19 ''' patch19: bare identifiers are now strings if no other interpretation possible
20 ''' patch19: -s now returns size of file
21 ''' patch19: Added __LINE__ and __FILE__ tokens
22 ''' patch19: Added __END__ token
24 ''' Revision 3.0.1.6 90/08/03 11:14:44 lwall
25 ''' patch19: Intermediate diffs for Randal
27 ''' Revision 3.0.1.5 90/03/27 16:14:37 lwall
28 ''' patch16: .. now works using magical string increment
30 ''' Revision 3.0.1.4 90/03/12 16:44:33 lwall
31 ''' patch13: (LIST,) now legal
32 ''' patch13: improved LIST documentation
33 ''' patch13: example of if-elsif switch was wrong
35 ''' Revision 3.0.1.3 90/02/28 17:54:32 lwall
36 ''' patch9: @array in scalar context now returns length of array
37 ''' patch9: in manual, example of open and ?: was backwards
39 ''' Revision 3.0.1.2 89/11/17 15:30:03 lwall
40 ''' patch5: fixed some manual typos and indent problems
42 ''' Revision 3.0.1.1 89/11/11 04:41:22 lwall
43 ''' patch2: explained about sh and ${1+"$@"}
44 ''' patch2: documented that space must separate word and '' string
46 ''' Revision 3.0 89/10/18 15:21:29 lwall
63 .ie \\n(.$>=3 .ne \\$3
68 ''' Set up \*(-- to give an unbreakable dash;
69 ''' string Tr holds user defined translation string.
70 ''' Bell System Logo is used as a dummy character.
75 .if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
76 .if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
93 perl \- Practical Extraction and Report Language
96 [options] filename args
99 is an interpreted language optimized for scanning arbitrary text files,
100 extracting information from those text files, and printing reports based
102 It's also a good language for many system management tasks.
103 The language is intended to be practical (easy to use, efficient, complete)
104 rather than beautiful (tiny, elegant, minimal).
105 It combines (in the author's opinion, anyway) some of the best features of C,
106 \fIsed\fR, \fIawk\fR, and \fIsh\fR,
107 so people familiar with those languages should have little difficulty with it.
108 (Language historians will also note some vestiges of \fIcsh\fR, Pascal, and
110 Expression syntax corresponds quite closely to C expression syntax.
111 Unlike most Unix utilities,
113 does not arbitrarily limit the size of your data\*(--if you've got
116 can slurp in your whole file as a single string.
117 Recursion is of unlimited depth.
118 And the hash tables used by associative arrays grow as necessary to prevent
119 degraded performance.
121 uses sophisticated pattern matching techniques to scan large amounts of
123 Although optimized for scanning text,
125 can also deal with binary data, and can make dbm files look like associative
126 arrays (where dbm is available).
129 scripts are safer than C programs
130 through a dataflow tracing mechanism which prevents many stupid security holes.
131 If you have a problem that would ordinarily use \fIsed\fR
132 or \fIawk\fR or \fIsh\fR, but it
133 exceeds their capabilities or must run a little faster,
134 and you don't want to write the silly thing in C, then
137 There are also translators to turn your
148 looks for your script in one of the following places:
150 Specified line by line via
152 switches on the command line.
154 Contained in the file specified by the first filename on the command line.
155 (Note that systems supporting the #! notation invoke interpreters this way.)
157 Passed in implicitly via standard input.
158 This only works if there are no filename arguments\*(--to pass
161 script you must explicitly specify a \- for the script name.
163 After locating your script,
165 compiles it to an internal form.
166 If the script is syntactically correct, it is executed.
168 Note: on first reading this section may not make much sense to you. It's here
169 at the front for easy reference.
171 A single-character option may be combined with the following option, if any.
172 This is particularly useful when invoking a script using the #! construct which
173 only allows one argument. Example:
177 #!/usr/bin/perl \-spi.bak # same as \-s \-p \-i.bak
184 turns on autosplit mode when used with a
188 An implicit split command to the @F array
189 is done as the first thing inside the implicit while loop produced by
196 perl \-ane \'print pop(@F), "\en";\'
202 print pop(@F), "\en";
210 to check the syntax of the script and then exit without executing it.
213 runs the script under the perl debugger.
214 See the section on Debugging.
217 sets debugging flags.
218 To watch how it executes your script, use
220 (This only works if debugging is compiled into your
222 Another nice value is \-D1024, which lists your compiled syntax tree.
223 And \-D512 displays compiled regular expressions.
225 .BI \-e " commandline"
226 may be used to enter one line of script.
229 commands may be given to build up a multi-line script.
234 will not look for a script filename in the argument list.
237 specifies that files processed by the <> construct are to be edited
239 It does this by renaming the input file, opening the output file by the
240 same name, and selecting that output file as the default for print statements.
241 The extension, if supplied, is added to the name of the
242 old file to make a backup copy.
243 If no extension is supplied, no backup is made.
244 Saying \*(L"perl \-p \-i.bak \-e "s/foo/bar/;" .\|.\|. \*(R" is the same as using
249 #!/usr/bin/perl \-pi.bak
252 which is equivalent to
257 if ($ARGV ne $oldargv) {
258 rename($ARGV, $ARGV . \'.bak\');
259 open(ARGVOUT, ">$ARGV");
266 print; # this prints to original filename
273 form doesn't need to compare $ARGV to $oldargv to know when
274 the filename has changed.
275 It does, however, use ARGVOUT for the selected filehandle.
278 is restored as the default output filehandle after the loop.
280 You can use eof to locate the end of each input file, in case you want
281 to append to each file, or reset line numbering (see example under eof).
284 may be used in conjunction with
286 to tell the C preprocessor where to look for include files.
287 By default /usr/include and /usr/lib/perl are searched.
292 to assume the following loop around your script, which makes it iterate
293 over filename arguments somewhat like \*(L"sed \-n\*(R" or \fIawk\fR:
298 .\|.\|. # your script goes here
302 Note that the lines are not printed by default.
305 to have lines printed.
306 Here is an efficient way to delete all files older than a week:
309 find . \-mtime +7 \-print | perl \-ne \'chop;unlink;\'
312 This is faster than using the \-exec switch of find because you don't have to
313 start a process on every filename found.
318 to assume the following loop around your script, which makes it iterate
319 over filename arguments somewhat like \fIsed\fR:
324 .\|.\|. # your script goes here
330 Note that the lines are printed automatically.
331 To suppress printing use the
341 causes your script to be run through the C preprocessor before
344 (Since both comments and cpp directives begin with the # character,
345 you should avoid starting comments with any words recognized
346 by the C preprocessor such as \*(L"if\*(R", \*(L"else\*(R" or \*(L"define\*(R".)
349 enables some rudimentary switch parsing for switches on the command line
350 after the script name but before any filename arguments (or before a \-\|\-).
351 Any switch found there is removed from @ARGV and sets the corresponding variable in the
354 The following script prints \*(L"true\*(R" if and only if the script is
355 invoked with a \-xyz switch.
360 if ($xyz) { print "true\en"; }
367 use the PATH environment variable to search for the script
368 (unless the name of the script starts with a slash).
369 Typically this is used to emulate #! startup on machines that don't
370 support #!, in the following manner:
374 eval "exec /usr/bin/perl \-S $0 $*"
375 if $running_under_some_shell;
378 The system ignores the first line and feeds the script to /bin/sh,
379 which proceeds to try to execute the
381 script as a shell script.
382 The shell executes the second line as a normal shell command, and thus
386 On some systems $0 doesn't always contain the full pathname,
391 to search for the script if necessary.
394 locates the script, it parses the lines and ignores them because
395 the variable $running_under_some_shell is never true.
396 A better construct than $* would be ${1+"$@"}, which handles embedded spaces
397 and such in the filenames, but doesn't work if the script is being interpreted
399 In order to start up sh rather than csh, some systems may have to replace the
400 #! line with a line containing just
401 a colon, which will be politely ignored by perl.
402 Other systems can't control that, and need a totally devious construct that
403 will work under any of csh, sh or perl, such as the following:
407 eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
408 & eval 'exec /usr/bin/perl -S $0 $argv:q'
416 to dump core after compiling your script.
417 You can then take this core dump and turn it into an executable file
418 by using the undump program (not supplied).
419 This speeds startup at the expense of some disk space (which you can
420 minimize by stripping the executable).
421 (Still, a "hello world" executable comes out to about 200K on my machine.)
422 If you are going to run your executable as a set-id program then you
423 should probably compile it using taintperl rather than normal perl.
424 If you want to execute a portion of your script before dumping, use the
425 dump operator instead.
426 Note: availability of undump is platform specific and may not be available
427 for a specific port of perl.
432 to do unsafe operations.
433 Currently the only \*(L"unsafe\*(R" operation is the unlinking of directories while
434 running as superuser.
437 prints the version and patchlevel of your
442 prints warnings about identifiers that are mentioned only once, and scalar
443 variables that are used before being set.
444 Also warns about redefined subroutines, and references to undefined
445 filehandles or filehandles opened readonly that you are attempting to
447 Also warns you if you use == on values that don't look like numbers, and if
448 your subroutines recurse more than 100 deep.
453 that the script is embedded in a message.
454 Leading garbage will be discarded until the first line that starts
455 with #! and contains the string "perl".
456 Any meaningful switches on that line will be applied (but only one
457 group of switches, as with normal #! processing).
458 If a directory name is specified, Perl will switch to that directory
459 before running the script.
462 switch only controls the the disposal of leading garbage.
463 The script must be terminated with __END__ if there is trailing garbage
464 to be ignored (the script can process any or all of the trailing garbage
465 via the DATA filehandle if desired).
466 .Sh "Data Types and Objects"
469 has three data types: scalars, arrays of scalars, and
470 associative arrays of scalars.
471 Normal arrays are indexed by number, and associative arrays by string.
473 The interpretation of operations and values in perl sometimes
474 depends on the requirements
475 of the context around the operation or value.
476 There are three major contexts: string, numeric and array.
477 Certain operations return array values
478 in contexts wanting an array, and scalar values otherwise.
479 (If this is true of an operation it will be mentioned in the documentation
481 Operations which return scalars don't care whether the context is looking
482 for a string or a number, but
483 scalar variables and values are interpreted as strings or numbers
484 as appropriate to the context.
485 A scalar is interpreted as TRUE in the boolean sense if it is not the null
487 Booleans returned by operators are 1 for true and 0 or \'\' (the null
490 There are actually two varieties of null string: defined and undefined.
491 Undefined null strings are returned when there is no real value for something,
492 such as when there was an error, or at end of file, or when you refer
493 to an uninitialized variable or element of an array.
494 An undefined null string may become defined the first time you access it, but
495 prior to that you can use the defined() operator to determine whether the
496 value is defined or not.
498 References to scalar variables always begin with \*(L'$\*(R', even when referring
499 to a scalar that is part of an array.
504 $days \h'|2i'# a simple scalar variable
505 $days[28] \h'|2i'# 29th element of array @days
506 $days{\'Feb\'}\h'|2i'# one value from an associative array
507 $#days \h'|2i'# last index of array @days
509 but entire arrays or array slices are denoted by \*(L'@\*(R':
511 @days \h'|2i'# ($days[0], $days[1],\|.\|.\|. $days[n])
512 @days[3,4,5]\h'|2i'# same as @days[3.\|.5]
513 @days{'a','c'}\h'|2i'# same as ($days{'a'},$days{'c'})
515 and entire associative arrays are denoted by \*(L'%\*(R':
517 %days \h'|2i'# (key1, val1, key2, val2 .\|.\|.)
520 Any of these eight constructs may serve as an lvalue,
521 that is, may be assigned to.
522 (It also turns out that an assignment is itself an lvalue in
523 certain contexts\*(--see examples under s, tr and chop.)
524 Assignment to a scalar evaluates the righthand side in a scalar context,
525 while assignment to an array or array slice evaluates the righthand side
528 You may find the length of array @days by evaluating
529 \*(L"$#days\*(R", as in
531 (Actually, it's not the length of the array, it's the subscript of the last element, since there is (ordinarily) a 0th element.)
532 Assigning to $#days changes the length of the array.
533 Shortening an array by this method does not actually destroy any values.
534 Lengthening an array that was previously shortened recovers the values that
535 were in those elements.
536 You can also gain some measure of efficiency by preextending an array that
538 (You can also extend an array by assigning to an element that is off the
540 This differs from assigning to $#whatever in that intervening values
541 are set to null rather than recovered.)
542 You can truncate an array down to nothing by assigning the null list () to
544 The following are exactly equivalent
548 $#whatever = $[ \- 1;
552 If you evaluate an array in a scalar context, it returns the length of
554 The following is always true:
557 @whatever == $#whatever \- $[ + 1;
561 Multi-dimensional arrays are not directly supported, but see the discussion
562 of the $; variable later for a means of emulating multiple subscripts with
563 an associative array.
564 You could also write a subroutine to turn multiple subscripts into a single
567 Every data type has its own namespace.
568 You can, without fear of conflict, use the same name for a scalar variable,
569 an array, an associative array, a filehandle, a subroutine name, and/or
571 Since variable and array references always start with \*(L'$\*(R', \*(L'@\*(R',
572 or \*(L'%\*(R', the \*(L"reserved\*(R" words aren't in fact reserved
573 with respect to variable names.
574 (They ARE reserved with respect to labels and filehandles, however, which
575 don't have an initial special character.
576 Hint: you could say open(LOG,\'logfile\') rather than open(log,\'logfile\').
577 Using uppercase filehandles also improves readability and protects you
578 from conflict with future reserved words.)
579 Case IS significant\*(--\*(L"FOO\*(R", \*(L"Foo\*(R" and \*(L"foo\*(R" are all
581 Names which start with a letter may also contain digits and underscores.
582 Names which do not start with a letter are limited to one character,
583 e.g. \*(L"$%\*(R" or \*(L"$$\*(R".
584 (Most of the one character names have a predefined significance to
588 Numeric literals are specified in any of the usual floating point or
600 String literals are delimited by either single or double quotes.
601 They work much like shell quotes:
602 double-quoted string literals are subject to backslash and variable
603 substitution; single-quoted strings are not (except for \e\' and \e\e).
604 The usual backslash rules apply for making characters such as newline, tab, etc.
605 You can also embed newlines directly in your strings, i.e. they can end on
606 a different line than they begin.
607 This is nice, but if you forget your trailing quote, the error will not be
610 finds another line containing the quote character, which
611 may be much further on in the script.
612 Variable substitution inside strings is limited to scalar variables, normal
613 array values, and array slices.
614 (In other words, identifiers beginning with $ or @, followed by an optional
615 bracketed expression as a subscript.)
616 The following code segment prints out \*(L"The price is $100.\*(R"
620 $Price = \'$100\';\h'|3.5i'# not interpreted
621 print "The price is $Price.\e\|n";\h'|3.5i'# interpreted
624 Note that you can put curly brackets around the identifier to delimit it
625 from following alphanumerics.
626 Also note that a single quoted string must be separated from a preceding
627 word by a space, since single quote is a valid character in an identifier
630 Two special literals are __LINE__ and __FILE__, which represent the current
631 line number and filename at that point in your program.
632 They may only be used as separate tokens; they will not be interpolated
634 In addition, the token __END__ may be used to indicate the logical end of the
635 script before the actual end of file.
636 Any following text is ignored (but may be read via the DATA filehandle).
637 The two control characters ^D and ^Z are synonyms for __END__.
639 A word that doesn't have any other interpretation in the grammar will be
640 treated as if it had single quotes around it.
641 For this purpose, a word consists only of alphanumeric characters and underline,
642 and must start with an alphabetic character.
643 As with filehandles and labels, a bare word that consists entirely of
644 lowercase letters risks conflict with future reserved words, and if you
647 switch, Perl will warn you about any such words.
649 Array values are interpolated into double-quoted strings by joining all the
650 elements of the array with the delimiter specified in the $" variable,
652 (Since in versions of perl prior to 3.0 the @ character was not a metacharacter
653 in double-quoted strings, the interpolation of @array, $array[EXPR],
654 @array[LIST], $array{EXPR}, or @array{LIST} only happens if array is
655 referenced elsewhere in the program or is predefined.)
656 The following are equivalent:
660 $temp = join($",@ARGV);
666 Within search patterns (which also undergo double-quotish substitution)
667 there is a bad ambiguity: Is /$foo[bar]/ to be
668 interpreted as /${foo}[bar]/ (where [bar] is a character class for the
669 regular expression) or as /${foo[bar]}/ (where [bar] is the subscript to
671 If @foo doesn't otherwise exist, then it's obviously a character class.
672 If @foo exists, perl takes a good guess about [bar], and is almost always right.
673 If it does guess wrong, or if you're just plain paranoid,
674 you can force the correct interpretation with curly brackets as above.
676 A line-oriented form of quoting is based on the shell here-is syntax.
677 Following a << you specify a string to terminate the quoted material, and all lines
678 following the current line down to the terminating string are the value
680 The terminating string may be either an identifier (a word), or some
682 If quoted, the type of quotes you use determines the treatment of the text,
683 just as in regular quoting.
684 An unquoted identifier works like double quotes.
685 There must be no space between the << and the identifier.
686 (If you put a space it will be treated as a null identifier, which is
687 valid, and matches the first blank line\*(--see Merry Christmas example below.)
688 The terminating string must appear by itself (unquoted and with no surrounding
689 whitespace) on the terminating line.
692 print <<EOF; # same as above
696 print <<"EOF"; # same as above
700 print << x 10; # null identifier is delimiter
703 print <<`EOC`; # execute commands
708 print <<foo, <<bar; # you can stack them
715 Array literals are denoted by separating individual values by commas, and
716 enclosing the list in parentheses:
722 In a context not requiring an array value, the value of the array literal
723 is the value of the final element, as in the C comma operator.
728 @foo = (\'cc\', \'\-E\', $bar);
730 assigns the entire array value to array foo, but
732 $foo = (\'cc\', \'\-E\', $bar);
735 assigns the value of variable bar to variable foo.
736 Note that the value of an actual array in a scalar context is the length
737 of the array; the following assigns to $foo the value 3:
741 @foo = (\'cc\', \'\-E\', $bar);
742 $foo = @foo; # $foo gets 3
745 You may have an optional comma before the closing parenthesis of an
746 array literal, so that you can say:
756 When a LIST is evaluated, each element of the list is evaluated in
757 an array context, and the resulting array value is interpolated into LIST
758 just as if each individual element were a member of LIST. Thus arrays
759 lose their identity in a LIST\*(--the list
763 contains all the elements of @foo followed by all the elements of @bar,
764 followed by all the elements returned by the subroutine named SomeSub.
766 A list value may also be subscripted like a normal array.
770 $time = (stat($file))[8]; # stat returns array value
771 $digit = ('a','b','c','d','e','f')[$digit-10];
772 return (pop(@foo),pop(@foo))[0];
776 Array lists may be assigned to if and only if each element of the list
780 ($a, $b, $c) = (1, 2, 3);
782 ($map{\'red\'}, $map{\'blue\'}, $map{\'green\'}) = (0x00f, 0x0f0, 0xf00);
784 The final element may be an array or an associative array:
786 ($a, $b, @rest) = split;
787 local($a, $b, %rest) = @_;
790 You can actually put an array anywhere in the list, but the first array
791 in the list will soak up all the values, and anything after it will get
793 This may be useful in a local().
795 An associative array literal contains pairs of values to be interpreted
796 as a key and a value:
800 # same as map assignment above
801 %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
804 Array assignment in a scalar context returns the number of elements
805 produced by the expression on the right side of the assignment:
808 $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
812 There are several other pseudo-literals that you should know about.
813 If a string is enclosed by backticks (grave accents), it first undergoes
814 variable substitution just like a double quoted string.
815 It is then interpreted as a command, and the output of that command
816 is the value of the pseudo-literal, like in a shell.
817 In a scalar context, a single string consisting of all the output is
819 In an array context, an array of values is returned, one for each line
821 (You can set $/ to use a different line terminator.)
822 The command is executed each time the pseudo-literal is evaluated.
823 The status value of the command is returned in $? (see Predefined Names
824 for the interpretation of $?).
825 Unlike in \f2csh\f1, no translation is done on the return
826 data\*(--newlines remain newlines.
827 Unlike in any of the shells, single quotes do not hide variable names
828 in the command from interpretation.
829 To pass a $ through to the shell you need to hide it with a backslash.
831 Evaluating a filehandle in angle brackets yields the next line
832 from that file (newline included, so it's never false until EOF, at
833 which time an undefined value is returned).
834 Ordinarily you must assign that value to a variable,
835 but there is one situation where an automatic assignment happens.
836 If (and only if) the input symbol is the only thing inside the conditional of a
839 automatically assigned to the variable \*(L"$_\*(R".
840 (This may seem like an odd thing to you, but you'll use the construct
844 Anyway, the following lines are equivalent to each other:
848 while ($_ = <STDIN>) { print; }
849 while (<STDIN>) { print; }
850 for (\|;\|<STDIN>;\|) { print; }
851 print while $_ = <STDIN>;
866 will also work except in packages, where they would be interpreted as
867 local identifiers rather than global.)
868 Additional filehandles may be created with the
872 If a <FILEHANDLE> is used in a context that is looking for an array, an array
873 consisting of all the input lines is returned, one line per array element.
874 It's easy to make a LARGE data space this way, so use with care.
876 The null filehandle <> is special and can be used to emulate the behavior of
877 \fIsed\fR and \fIawk\fR.
878 Input from <> comes either from standard input, or from each file listed on
880 Here's how it works: the first time <> is evaluated, the ARGV array is checked,
881 and if it is null, $ARGV[0] is set to \'-\', which when opened gives you standard
883 The ARGV array is then processed as a list of filenames.
889 .\|.\|. # code for each line
895 unshift(@ARGV, \'\-\') \|if \|$#ARGV < $[;
896 while ($ARGV = shift) {
899 .\|.\|. # code for each line
904 except that it isn't as cumbersome to say.
905 It really does shift array ARGV and put the current filename into
907 It also uses filehandle ARGV internally.
908 You can modify @ARGV before the first <> as long as you leave the first
909 filename at the beginning of the array.
910 Line numbers ($.) continue as if the input was one big happy file.
911 (But see example under eof for how to reset line numbers on each file.)
914 If you want to set @ARGV to your own list of files, go right ahead.
915 If you want to pass switches into your script, you can
916 put a loop on the front like this:
920 while ($_ = $ARGV[0], /\|^\-/\|) {
922 last if /\|^\-\|\-$\|/\|;
923 /\|^\-D\|(.*\|)/ \|&& \|($debug = $1);
924 /\|^\-v\|/ \|&& \|$verbose++;
925 .\|.\|. # other switches
928 .\|.\|. # code for each line
932 The <> symbol will return FALSE only once.
933 If you call it again after this it will assume you are processing another
934 @ARGV list, and if you haven't set @ARGV, will input from
937 If the string inside the angle brackets is a reference to a scalar variable
939 then that variable contains the name of the filehandle to input from.
941 If the string inside angle brackets is not a filehandle, it is interpreted
942 as a filename pattern to be globbed, and either an array of filenames or the
943 next filename in the list is returned, depending on context.
944 One level of $ interpretation is done first, but you can't say <$foo>
945 because that's an indirect filehandle as explained in the previous
947 You could insert curly brackets to force interpretation as a
948 filename glob: <${foo}>.
960 open(foo, "echo *.c | tr \-s \' \et\er\ef\' \'\e\e012\e\e012\e\e012\e\e012\'|");
967 In fact, it's currently implemented that way.
968 (Which means it will not work on filenames with spaces in them unless
969 you have /bin/csh on your machine.)
970 Of course, the shortest way to do the above is:
980 script consists of a sequence of declarations and commands.
981 The only things that need to be declared in
983 are report formats and subroutines.
984 See the sections below for more information on those declarations.
985 All uninitialized user-created objects are assumed to
986 start with a null or 0 value until they
987 are defined by some explicit operation such as assignment.
988 The sequence of commands is executed just once, unlike in
992 scripts, where the sequence of commands is executed for each input line.
993 While this means that you must explicitly loop over the lines of your input file
994 (or files), it also means you have much more control over which files and which
996 (Actually, I'm lying\*(--it is possible to do an implicit loop with either the
1002 A declaration can be put anywhere a command can, but has no effect on the
1003 execution of the primary sequence of commands\(*--declarations all take effect
1005 Typically all the declarations are put at the beginning or the end of the script.
1008 is, for the most part, a free-form language.
1009 (The only exception to this is format declarations, for fairly obvious reasons.)
1010 Comments are indicated by the # character, and extend to the end of the line.
1011 If you attempt to use /* */ C comments, it will be interpreted either as
1012 division or pattern matching, depending on the context.
1014 .Sh "Compound statements"
1017 a sequence of commands may be treated as one command by enclosing it
1019 We will call this a BLOCK.
1021 The following compound commands may be used to control flow:
1026 if (EXPR) BLOCK else BLOCK
1027 if (EXPR) BLOCK elsif (EXPR) BLOCK .\|.\|. else BLOCK
1028 LABEL while (EXPR) BLOCK
1029 LABEL while (EXPR) BLOCK continue BLOCK
1030 LABEL for (EXPR; EXPR; EXPR) BLOCK
1031 LABEL foreach VAR (ARRAY) BLOCK
1032 LABEL BLOCK continue BLOCK
1035 Note that, unlike C and Pascal, these are defined in terms of BLOCKs, not
1037 This means that the curly brackets are \fIrequired\fR\*(--no dangling statements allowed.
1038 If you want to write conditionals without curly brackets there are several
1039 other ways to do it.
1040 The following all do the same thing:
1044 if (!open(foo)) { die "Can't open $foo: $!"; }
1045 die "Can't open $foo: $!" unless open(foo);
1046 open(foo) || die "Can't open $foo: $!"; # foo or bust!
1047 open(foo) ? \'hi mom\' : die "Can't open $foo: $!";
1048 # a bit exotic, that last one
1054 statement is straightforward.
1055 Since BLOCKs are always bounded by curly brackets, there is never any
1056 ambiguity about which
1065 the sense of the test is reversed.
1069 statement executes the block as long as the expression is true
1070 (does not evaluate to the null string or 0).
1071 The LABEL is optional, and if present, consists of an identifier followed by
1073 The LABEL identifies the loop for the loop control statements
1081 BLOCK, it is always executed just before
1082 the conditional is about to be evaluated again, similarly to the third part
1086 Thus it can be used to increment a loop variable, even when the loop has
1087 been continued via the
1089 statement (similar to the C \*(L"continue\*(R" statement).
1093 is replaced by the word
1095 the sense of the test is reversed, but the conditional is still tested before
1096 the first iteration.
1102 statement, you may replace \*(L"(EXPR)\*(R" with a BLOCK, and the conditional
1103 is true if the value of the last command in that block is true.
1107 loop works exactly like the corresponding
1113 for ($i = 1; $i < 10; $i++) {
1127 The foreach loop iterates over a normal array value and sets the variable
1128 VAR to be each element of the array in turn.
1129 The variable is implicitly local to the loop, and regains its former value
1130 upon exiting the loop.
1131 The \*(L"foreach\*(R" keyword is actually identical to the \*(L"for\*(R" keyword,
1132 so you can use \*(L"foreach\*(R" for readability or \*(L"for\*(R" for brevity.
1133 If VAR is omitted, $_ is set to each value.
1134 If ARRAY is an actual array (as opposed to an expression returning an array
1135 value), you can modify each element of the array
1136 by modifying VAR inside the loop.
1141 for (@ary) { s/foo/bar/; }
1143 foreach $elem (@elements) {
1148 for ((10,9,8,7,6,5,4,3,2,1,\'BOOM\')) {
1149 print $_, "\en"; sleep(1);
1152 for (1..15) { print "Merry Christmas\en"; }
1155 foreach $item (split(/:[\e\e\en:]*/, $ENV{\'TERMCAP\'})) {
1156 print "Item: $item\en";
1161 The BLOCK by itself (labeled or not) is equivalent to a loop that executes
1163 Thus you can use any of the loop control statements in it to leave or
1168 This construct is particularly nice for doing case structures.
1173 if (/^abc/) { $abc = 1; last foo; }
1174 if (/^def/) { $def = 1; last foo; }
1175 if (/^xyz/) { $xyz = 1; last foo; }
1180 There is no official switch statement in perl, because there
1181 are already several ways to write the equivalent.
1182 In addition to the above, you could write
1187 $abc = 1, last foo if /^abc/;
1188 $def = 1, last foo if /^def/;
1189 $xyz = 1, last foo if /^xyz/;
1197 /^abc/ && do { $abc = 1; last foo; };
1198 /^def/ && do { $def = 1; last foo; };
1199 /^xyz/ && do { $xyz = 1; last foo; };
1207 /^abc/ && ($abc = 1, last foo);
1208 /^def/ && ($def = 1, last foo);
1209 /^xyz/ && ($xyz = 1, last foo);
1226 As it happens, these are all optimized internally to a switch structure,
1227 so perl jumps directly to the desired statement, and you needn't worry
1228 about perl executing a lot of unnecessary statements when you have a string
1229 of 50 elsifs, as long as you are testing the same simple scalar variable
1230 using ==, eq, or pattern matching as above.
1231 (If you're curious as to whether the optimizer has done this for a particular
1232 case statement, you can use the \-D1024 switch to list the syntax tree
1234 .Sh "Simple statements"
1235 The only kind of simple statement is an expression evaluated for its side
1237 Every expression (simple statement) must be terminated with a semicolon.
1238 Note that this is like C, but unlike Pascal (and
1241 Any simple statement may optionally be followed by a
1242 single modifier, just before the terminating semicolon.
1243 The possible modifiers are:
1257 modifiers have the expected semantics.
1262 modifiers also have the expected semantics (conditional evaluated first),
1263 except when applied to a do-BLOCK command,
1264 in which case the block executes once before the conditional is evaluated.
1265 This is so that you can write loops like:
1272 } until $_ \|eq \|".\|\e\|n";
1277 operator below. Note also that the loop control commands described later will
1278 NOT work in this construct, since modifiers don't take loop labels.
1283 expressions work almost exactly like C expressions, only the differences
1284 will be mentioned here.
1290 The exponentiation operator.
1292 The exponentiation assignment operator.
1294 The null list, used to initialize an array to null.
1296 Concatenation of two strings.
1298 The concatenation assignment operator.
1300 String equality (== is numeric equality).
1301 For a mnemonic just think of \*(L"eq\*(R" as a string.
1302 (If you are used to the
1304 behavior of using == for either string or numeric equality
1305 based on the current form of the comparands, beware!
1306 You must be explicit here.)
1308 String inequality (!= is numeric inequality).
1312 String greater than.
1314 String less than or equal.
1316 String greater than or equal.
1318 String comparison, returning -1, 0, or 1.
1320 Numeric comparison, returning -1, 0, or 1.
1322 Certain operations search or modify the string \*(L"$_\*(R" by default.
1323 This operator makes that kind of operation work on some other string.
1324 The right argument is a search pattern, substitution, or translation.
1325 The left argument is what is supposed to be searched, substituted, or
1326 translated instead of the default \*(L"$_\*(R".
1327 The return value indicates the success of the operation.
1328 (If the right argument is an expression other than a search pattern,
1329 substitution, or translation, it is interpreted as a search pattern
1331 This is less efficient than an explicit search, since the pattern must
1332 be compiled every time the expression is evaluated.)
1333 The precedence of this operator is lower than unary minus and autoincrement/decrement, but higher than everything else.
1335 Just like =~ except the return value is negated.
1337 The repetition operator.
1338 Returns a string consisting of the left operand repeated the
1339 number of times specified by the right operand.
1342 print \'\-\' x 80; # print row of dashes
1343 print \'\-\' x80; # illegal, x80 is identifier
1345 print "\et" x ($tab/8), \' \' x ($tab%8); # tab over
1349 The repetition assignment operator.
1351 The range operator, which is really two different operators depending
1353 In an array context, returns an array of values counting (by ones)
1354 from the left value to the right value.
1355 This is useful for writing \*(L"for (1..10)\*(R" loops and for doing
1356 slice operations on arrays.
1358 In a scalar context, .\|. returns a boolean value.
1359 The operator is bistable, like a flip-flop..
1360 Each .\|. operator maintains its own boolean state.
1361 It is false as long as its left operand is false.
1362 Once the left operand is true, the range operator stays true
1363 until the right operand is true,
1364 AFTER which the range operator becomes false again.
1365 (It doesn't become false till the next time the range operator is evaluated.
1366 It can become false on the same evaluation it became true, but it still returns
1368 The right operand is not evaluated while the operator is in the \*(L"false\*(R" state,
1369 and the left operand is not evaluated while the operator is in the \*(L"true\*(R" state.
1370 The scalar .\|. operator is primarily intended for doing line number ranges
1372 the fashion of \fIsed\fR or \fIawk\fR.
1373 The precedence is a little lower than || and &&.
1374 The value returned is either the null string for false, or a sequence number
1375 (beginning with 1) for true.
1376 The sequence number is reset for each range encountered.
1377 The final sequence number in a range has the string \'E0\' appended to it, which
1378 doesn't affect its numeric value, but gives you something to search for if you
1379 want to exclude the endpoint.
1380 You can exclude the beginning point by waiting for the sequence number to be
1382 If either operand of scalar .\|. is static, that operand is implicitly compared
1383 to the $. variable, the current line number.
1388 As a scalar operator:
1389 if (101 .\|. 200) { print; } # print 2nd hundred lines
1391 next line if (1 .\|. /^$/); # skip header lines
1393 s/^/> / if (/^$/ .\|. eof()); # quote body
1396 As an array operator:
1397 for (101 .\|. 200) { print; } # print $_ 100 times
1399 @foo = @foo[$[ .\|. $#foo]; # an expensive no-op
1400 @foo = @foo[$#foo-4 .\|. $#foo]; # slice last 5 items
1405 This unary operator takes one argument, either a filename or a filehandle,
1406 and tests the associated file to see if something is true about it.
1407 If the argument is omitted, tests $_, except for \-t, which tests
1409 It returns 1 for true and \'\' for false, or the undefined value if the
1411 Precedence is higher than logical and relational operators, but lower than
1412 arithmetic operators.
1413 The operator may be any of:
1415 \-r File is readable by effective uid.
1416 \-w File is writable by effective uid.
1417 \-x File is executable by effective uid.
1418 \-o File is owned by effective uid.
1419 \-R File is readable by real uid.
1420 \-W File is writable by real uid.
1421 \-X File is executable by real uid.
1422 \-O File is owned by real uid.
1424 \-z File has zero size.
1425 \-s File has non-zero size (returns size).
1426 \-f File is a plain file.
1427 \-d File is a directory.
1428 \-l File is a symbolic link.
1429 \-p File is a named pipe (FIFO).
1430 \-S File is a socket.
1431 \-b File is a block special file.
1432 \-c File is a character special file.
1433 \-u File has setuid bit set.
1434 \-g File has setgid bit set.
1435 \-k File has sticky bit set.
1436 \-t Filehandle is opened to a tty.
1437 \-T File is a text file.
1438 \-B File is a binary file (opposite of \-T).
1439 \-M Age of file in days when script started.
1440 \-A Same for access time.
1441 \-C Same for inode change time.
1444 The interpretation of the file permission operators \-r, \-R, \-w, \-W, \-x and \-X
1445 is based solely on the mode of the file and the uids and gids of the user.
1446 There may be other reasons you can't actually read, write or execute the file.
1447 Also note that, for the superuser, \-r, \-R, \-w and \-W always return 1, and
1448 \-x and \-X return 1 if any execute bit is set in the mode.
1449 Scripts run by the superuser may thus need to do a stat() in order to determine
1450 the actual mode of the file, or temporarily set the uid to something else.
1458 next unless \-f $_; # ignore specials
1463 Note that \-s/a/b/ does not do a negated substitution.
1464 Saying \-exp($foo) still works as expected, however\*(--only single letters
1465 following a minus are interpreted as file tests.
1467 The \-T and \-B switches work as follows.
1468 The first block or so of the file is examined for odd characters such as
1469 strange control codes or metacharacters.
1470 If too many odd characters (>10%) are found, it's a \-B file, otherwise it's a \-T file.
1471 Also, any file containing null in the first block is considered a binary file.
1472 If \-T or \-B is used on a filehandle, the current stdio buffer is examined
1473 rather than the first block.
1474 Both \-T and \-B return TRUE on a null file, or a file at EOF when testing
1477 If any of the file tests (or either stat operator) are given the special
1478 filehandle consisting of a solitary underline, then the stat structure
1479 of the previous file test (or stat operator) is used, saving a system
1481 (This doesn't work with \-t, and you need to remember that lstat and -l
1482 will leave values in the stat structure for the symbolic link, not the
1487 print "Can do.\en" if -r $a || -w _ || -x _;
1491 print "Readable\en" if -r _;
1492 print "Writable\en" if -w _;
1493 print "Executable\en" if -x _;
1494 print "Setuid\en" if -u _;
1495 print "Setgid\en" if -g _;
1496 print "Sticky\en" if -k _;
1497 print "Text\en" if -T _;
1498 print "Binary\en" if -B _;
1502 Here is what C has that
1506 Address-of operator.
1508 Dereference-address operator.
1510 Type casting operator.
1514 does a certain amount of expression evaluation at compile time, whenever
1515 it determines that all of the arguments to an operator are static and have
1517 In particular, string concatenation happens at compile time between literals that don't do variable substitution.
1518 Backslash interpretation also happens at compile time.
1523 \'Now is the time for all\' . "\|\e\|n" .
1524 \'good men to come to.\'
1527 and this all reduces to one string internally.
1529 The autoincrement operator has a little extra built-in magic to it.
1530 If you increment a variable that is numeric, or that has ever been used in
1531 a numeric context, you get a normal increment.
1532 If, however, the variable has only been used in string contexts since it
1533 was set, and has a value that is not null and matches the
1534 pattern /^[a\-zA\-Z]*[0\-9]*$/, the increment is done
1535 as a string, preserving each character within its range, with carry:
1538 print ++($foo = \'99\'); # prints \*(L'100\*(R'
1539 print ++($foo = \'a0\'); # prints \*(L'a1\*(R'
1540 print ++($foo = \'Az\'); # prints \*(L'Ba\*(R'
1541 print ++($foo = \'zz\'); # prints \*(L'aaa\*(R'
1544 The autodecrement is not magical.
1546 The range operator (in an array context) makes use of the magical
1547 autoincrement algorithm if the minimum and maximum are strings.
1550 @alphabet = (\'A\' .. \'Z\');
1552 to get all the letters of the alphabet, or
1554 $hexdigit = (0 .. 9, \'a\' .. \'f\')[$num & 15];
1556 to get a hexadecimal digit, or
1558 @z2 = (\'01\' .. \'31\'); print @z2[$mday];
1560 to get dates with leading zeros.
1561 (If the final value specified is not in the sequence that the magical increment
1562 would produce, the sequence goes until the next value would be longer than
1563 the final value specified.)
1565 The || and && operators differ from C's in that, rather than returning 0 or 1,
1566 they return the last value evaluated.
1567 Thus, a portable way to find out the home directory might be:
1570 $home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
1571 (getpwuid($<))[7] || die "You're homeless!\en";