3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTtuUWX> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
12 S<[ B<-C [I<number/list>] >]>
16 S<[ B<-i>[I<extension>] ]>
17 S<[ B<-eE> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
21 The normal way to run a Perl program is by making it directly
22 executable, or else by passing the name of the source file as an
23 argument on the command line. (An interactive Perl environment
24 is also possible--see L<perldebug> for details on how to do that.)
25 Upon startup, Perl looks for your program in one of the following
32 Specified line by line via B<-e> or B<-E> switches on the command line.
36 Contained in the file specified by the first filename on the command line.
37 (Note that systems supporting the #! notation invoke interpreters this
38 way. See L<Location of Perl>.)
42 Passed in implicitly via standard input. This works only if there are
43 no filename arguments--to pass arguments to a STDIN-read program you
44 must explicitly specify a "-" for the program name.
48 With methods 2 and 3, Perl starts parsing the input file from the
49 beginning, unless you've specified a B<-x> switch, in which case it
50 scans for the first line starting with #! and containing the word
51 "perl", and starts there instead. This is useful for running a program
52 embedded in a larger message. (In this case you would indicate the end
53 of the program using the C<__END__> token.)
55 The #! line is always examined for switches as the line is being
56 parsed. Thus, if you're on a machine that allows only one argument
57 with the #! line, or worse, doesn't even recognize the #! line, you
58 still can get consistent switch behavior regardless of how Perl was
59 invoked, even if B<-x> was used to find the beginning of the program.
61 Because historically some operating systems silently chopped off
62 kernel interpretation of the #! line after 32 characters, some
63 switches may be passed in on the command line, and some may not;
64 you could even get a "-" without its letter, if you're not careful.
65 You probably want to make sure that all your switches fall either
66 before or after that 32-character boundary. Most switches don't
67 actually care if they're processed redundantly, but getting a "-"
68 instead of a complete switch could cause Perl to try to execute
69 standard input instead of your program. And a partial B<-I> switch
70 could also cause odd results.
72 Some switches do care if they are processed twice, for instance
73 combinations of B<-l> and B<-0>. Either put all the switches after
74 the 32-character boundary (if applicable), or replace the use of
75 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
77 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
78 The sequences "-*" and "- " are specifically ignored so that you could,
79 if you were so inclined, say
81 #!/bin/sh -- # -*- perl -*- -p
82 eval 'exec perl -wS $0 ${1+"$@"}'
83 if $running_under_some_shell;
85 to let Perl see the B<-p> switch.
87 A similar trick involves the B<env> program, if you have it.
91 The examples above use a relative path to the perl interpreter,
92 getting whatever version is first in the user's path. If you want
93 a specific version of Perl, say, perl5.005_57, you should place
94 that directly in the #! line's path.
96 If the #! line does not contain the word "perl", the program named after
97 the #! is executed instead of the Perl interpreter. This is slightly
98 bizarre, but it helps people on machines that don't do #!, because they
99 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
100 dispatch the program to the correct interpreter for them.
102 After locating your program, Perl compiles the entire program to an
103 internal form. If there are any compilation errors, execution of the
104 program is not attempted. (This is unlike the typical shell script,
105 which might run part-way through before finding a syntax error.)
107 If the program is syntactically correct, it is executed. If the program
108 runs off the end without hitting an exit() or die() operator, an implicit
109 C<exit(0)> is provided to indicate successful completion.
111 =head2 #! and quoting on non-Unix systems
114 Unix's #! technique can be simulated on other systems:
122 extproc perl -S -your_switches
124 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
129 Create a batch file to run your program, and codify it in
130 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
131 distribution for more information).
135 The Win95/NT installation, when using the ActiveState installer for Perl,
136 will modify the Registry to associate the F<.pl> extension with the perl
137 interpreter. If you install Perl by other means (including building from
138 the sources), you may have to modify the Registry yourself. Note that
139 this means you can no longer tell the difference between an executable
140 Perl program and a Perl library file.
144 Under "Classic" MacOS, a perl program will have the appropriate Creator and
145 Type, so that double-clicking them will invoke the MacPerl application.
146 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
147 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
153 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
154 $ exit++ + ++$status != 0 and $exit = $status = undef;
156 at the top of your program, where B<-mysw> are any command line switches you
157 want to pass to Perl. You can now invoke the program directly, by saying
158 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
159 via F<DCL$PATH> by just using the name of the program).
161 This incantation is a bit much to remember, but Perl will display it for
162 you if you say C<perl "-V:startperl">.
166 Command-interpreters on non-Unix systems have rather different ideas
167 on quoting than Unix shells. You'll need to learn the special
168 characters in your command-interpreter (C<*>, C<\> and C<"> are
169 common) and how to protect whitespace and these characters to run
170 one-liners (see B<-e> below).
172 On some systems, you may have to change single-quotes to double ones,
173 which you must I<not> do on Unix or Plan 9 systems. You might also
174 have to change a single % to a %%.
179 perl -e 'print "Hello world\n"'
182 perl -e "print \"Hello world\n\""
185 print "Hello world\n"
186 (then Run "Myscript" or Shift-Command-R)
189 perl -e "print ""Hello world\n"""
191 The problem is that none of this is reliable: it depends on the
192 command and it is entirely possible neither works. If B<4DOS> were
193 the command shell, this would probably work better:
195 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
197 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
198 when nobody was looking, but just try to find documentation for its
201 Under the Macintosh, it depends which environment you are using. The MacPerl
202 shell, or MPW, is much like Unix shells in its support for several
203 quoting variants, except that it makes free use of the Macintosh's non-ASCII
204 characters as control characters.
206 There is no general solution to all of this. It's just a mess.
208 =head2 Location of Perl
209 X<perl, location of interpreter>
211 It may seem obvious to say, but Perl is useful only when users can
212 easily find it. When possible, it's good for both F</usr/bin/perl>
213 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
214 that can't be done, system administrators are strongly encouraged
215 to put (symlinks to) perl and its accompanying utilities into a
216 directory typically found along a user's PATH, or in some other
217 obvious and convenient place.
219 In this documentation, C<#!/usr/bin/perl> on the first line of the program
220 will stand in for whatever method works on your system. You are
221 advised to use a specific path if you care about a specific version.
223 #!/usr/local/bin/perl5.00554
225 or if you just want to be running at least version, place a statement
226 like this at the top of your program:
230 =head2 Command Switches
231 X<perl, command switches> X<command switches>
233 As with all standard commands, a single-character switch may be
234 clustered with the following switch, if any.
236 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
242 =item B<-0>[I<octal/hexadecimal>]
245 specifies the input record separator (C<$/>) as an octal or
246 hexadecimal number. If there are no digits, the null character is the
247 separator. Other switches may precede or follow the digits. For
248 example, if you have a version of B<find> which can print filenames
249 terminated by the null character, you can say this:
251 find . -name '*.orig' -print0 | perl -n0e unlink
253 The special value 00 will cause Perl to slurp files in paragraph mode.
254 The value 0777 will cause Perl to slurp files whole because there is no
255 legal byte with that value.
257 If you want to specify any Unicode character, use the hexadecimal
258 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
259 (This means that you cannot use the C<-x> with a directory name that
260 consists of hexadecimal digits.)
265 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
266 split command to the @F array is done as the first thing inside the
267 implicit while loop produced by the B<-n> or B<-p>.
269 perl -ane 'print pop(@F), "\n";'
278 An alternate delimiter may be specified using B<-F>.
280 =item B<-C [I<number/list>]>
283 The C<-C> flag controls some of the Perl Unicode features.
285 As of 5.8.1, the C<-C> can be followed either by a number or a list
286 of option letters. The letters, their numeric values, and effects
287 are as follows; listing the letters is equal to summing the numbers.
289 I 1 STDIN is assumed to be in UTF-8
290 O 2 STDOUT will be in UTF-8
291 E 4 STDERR will be in UTF-8
293 i 8 UTF-8 is the default PerlIO layer for input streams
294 o 16 UTF-8 is the default PerlIO layer for output streams
296 A 32 the @ARGV elements are expected to be strings encoded
298 L 64 normally the "IOEioA" are unconditional,
299 the L makes them conditional on the locale environment
300 variables (the LC_ALL, LC_TYPE, and LANG, in the order
301 of decreasing precedence) -- if the variables indicate
302 UTF-8, then the selected "IOEioA" are in effect
303 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching code in
306 =for documenting_the_underdocumented
307 perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
310 perltodo mentions Unicode in %ENV and filenames. I guess that these will be
311 options e and f (or F).
313 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
314 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
317 The C<io> options mean that any subsequent open() (or similar I/O
318 operations) will have the C<:utf8> PerlIO layer implicitly applied
319 to them, in other words, UTF-8 is expected from any input stream,
320 and UTF-8 is produced to any output stream. This is just the default,
321 with explicit layers in open() and with binmode() one can manipulate
324 C<-C> on its own (not followed by any number or option list), or the
325 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
326 same effect as C<-CSDL>. In other words, the standard I/O handles and
327 the default C<open()> layer are UTF-8-fied B<but> only if the locale
328 environment variables indicate a UTF-8 locale. This behaviour follows
329 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
331 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
332 disable all the above Unicode features.
334 The read-only magic variable C<${^UNICODE}> reflects the numeric value
335 of this setting. This is variable is set during Perl startup and is
336 thereafter read-only. If you want runtime effects, use the three-arg
337 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
338 and the C<open> pragma (see L<open>).
340 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
341 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
342 This feature was practically unused, however, and the command line
343 switch was therefore "recycled".)
348 causes Perl to check the syntax of the program and then exit without
349 executing it. Actually, it I<will> execute C<BEGIN>, C<UNITCHECK>,
350 C<CHECK>, and C<use> blocks, because these are considered as occurring
351 outside the execution of your program. C<INIT> and C<END> blocks,
352 however, will be skipped.
359 runs the program under the Perl debugger. See L<perldebug>.
360 If B<t> is specified, it indicates to the debugger that threads
361 will be used in the code being debugged.
363 =item B<-d:>I<foo[=bar,baz]>
366 =item B<-dt:>I<foo[=bar,baz]>
368 runs the program under the control of a debugging, profiling, or
369 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
370 the program using the Devel::DProf profiler. As with the B<-M>
371 flag, options may be passed to the Devel::foo package where they
372 will be received and interpreted by the Devel::foo::import routine.
373 The comma-separated list of options must follow a C<=> character.
374 If B<t> is specified, it indicates to the debugger that threads
375 will be used in the code being debugged.
378 =item B<-D>I<letters>
379 X<-D> X<DEBUGGING> X<-DDEBUGGING>
383 sets debugging flags. To watch how it executes your program, use
384 B<-Dtls>. (This works only if debugging is compiled into your
385 Perl.) Another nice value is B<-Dx>, which lists your compiled
386 syntax tree. And B<-Dr> displays compiled regular expressions;
387 the format of the output is explained in L<perldebguts>.
389 As an alternative, specify a number instead of list of letters (e.g.,
390 B<-D14> is equivalent to B<-Dtls>):
392 1 p Tokenizing and parsing (with v, displays parse stack)
393 2 s Stack snapshots (with v, displays all stacks)
394 4 l Context (loop) stack processing
396 16 o Method and overloading resolution
397 32 c String/numeric conversions
398 64 P Print profiling info, preprocessor command for -P, source file input state
399 128 m Memory allocation
400 256 f Format processing
401 512 r Regular expression parsing and execution
402 1024 x Syntax tree dump
403 2048 u Tainting checks
404 4096 U Unofficial, User hacking (reserved for private, unreleased use)
405 8192 H Hash dump -- usurps values()
406 16384 X Scratchpad allocation
408 65536 S Thread synchronization
410 262144 R Include reference counts of dumped variables (eg when using -Ds)
411 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
412 1048576 v Verbose: use in conjunction with other flags
413 2097152 C Copy On Write
414 4194304 A Consistency checks on internal structures
415 8388608 q quiet - currently only suppresses the "EXECUTING" message
417 All these flags require B<-DDEBUGGING> when you compile the Perl
418 executable (but see L<Devel::Peek>, L<re> which may change this).
419 See the F<INSTALL> file in the Perl source distribution
420 for how to do this. This flag is automatically set if you include B<-g>
421 option when C<Configure> asks you about optimizer/debugger flags.
423 If you're just trying to get a print out of each line of Perl code
424 as it executes, the way that C<sh -x> provides for shell scripts,
425 you can't use Perl's B<-D> switch. Instead do this
427 # If you have "env" utility
428 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
430 # Bourne shell syntax
431 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
434 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
436 See L<perldebug> for details and variations.
438 =item B<-e> I<commandline>
441 may be used to enter one line of program. If B<-e> is given, Perl
442 will not look for a filename in the argument list. Multiple B<-e>
443 commands may be given to build up a multi-line script. Make sure
444 to use semicolons where you would in a normal program.
446 =item B<-E> I<commandline>
449 behaves just like B<-e>, except that it implicitly enables all
450 optional features (in the main compilation unit). See L<feature>.
455 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
457 Perl can be built so that it by default will try to execute
458 F<$Config{sitelib}/sitecustomize.pl> at startup. This is a hook that
459 allows the sysadmin to customize how perl behaves. It can for
460 instance be used to add entries to the @INC array to make perl find
461 modules in non-standard locations.
463 =item B<-F>I<pattern>
466 specifies the pattern to split on if B<-a> is also in effect. The
467 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
468 put in single quotes. You can't use literal whitespace in the pattern.
473 prints a summary of the options.
475 =item B<-i>[I<extension>]
478 specifies that files processed by the C<E<lt>E<gt>> construct are to be
479 edited in-place. It does this by renaming the input file, opening the
480 output file by the original name, and selecting that output file as the
481 default for print() statements. The extension, if supplied, is used to
482 modify the name of the old file to make a backup copy, following these
485 If no extension is supplied, no backup is made and the current file is
488 If the extension doesn't contain a C<*>, then it is appended to the
489 end of the current filename as a suffix. If the extension does
490 contain one or more C<*> characters, then each C<*> is replaced
491 with the current filename. In Perl terms, you could think of this
494 ($backup = $extension) =~ s/\*/$file_name/g;
496 This allows you to add a prefix to the backup file, instead of (or in
497 addition to) a suffix:
499 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
501 Or even to place backup copies of the original files into another
502 directory (provided the directory already exists):
504 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
506 These sets of one-liners are equivalent:
508 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
509 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
511 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
512 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
514 From the shell, saying
516 $ perl -p -i.orig -e "s/foo/bar/; ... "
518 is the same as using the program:
520 #!/usr/bin/perl -pi.orig
523 which is equivalent to
526 $extension = '.orig';
528 if ($ARGV ne $oldargv) {
529 if ($extension !~ /\*/) {
530 $backup = $ARGV . $extension;
533 ($backup = $extension) =~ s/\*/$ARGV/g;
535 rename($ARGV, $backup);
536 open(ARGVOUT, ">$ARGV");
543 print; # this prints to original filename
547 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
548 know when the filename has changed. It does, however, use ARGVOUT for
549 the selected filehandle. Note that STDOUT is restored as the default
550 output filehandle after the loop.
552 As shown above, Perl creates the backup file whether or not any output
553 is actually changed. So this is just a fancy way to copy files:
555 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
557 $ perl -p -i'.orig' -e 1 file1 file2 file3...
559 You can use C<eof> without parentheses to locate the end of each input
560 file, in case you want to append to each file, or reset line numbering
561 (see example in L<perlfunc/eof>).
563 If, for a given file, Perl is unable to create the backup file as
564 specified in the extension then it will skip that file and continue on
565 with the next one (if it exists).
567 For a discussion of issues surrounding file permissions and B<-i>,
568 see L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>.
570 You cannot use B<-i> to create directories or to strip extensions from
573 Perl does not expand C<~> in filenames, which is good, since some
574 folks use it for their backup files:
576 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
578 Note that because B<-i> renames or deletes the original file before
579 creating a new file of the same name, UNIX-style soft and hard links will
582 Finally, the B<-i> switch does not impede execution when no
583 files are given on the command line. In this case, no backup is made
584 (the original file cannot, of course, be determined) and processing
585 proceeds from STDIN to STDOUT as might be expected.
587 =item B<-I>I<directory>
590 Directories specified by B<-I> are prepended to the search path for
591 modules (C<@INC>), and also tells the C preprocessor where to search for
592 include files. The C preprocessor is invoked with B<-P>; by default it
593 searches /usr/include and /usr/lib/perl.
595 =item B<-l>[I<octnum>]
598 enables automatic line-ending processing. It has two separate
599 effects. First, it automatically chomps C<$/> (the input record
600 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
601 (the output record separator) to have the value of I<octnum> so
602 that any print statements will have that separator added back on.
603 If I<octnum> is omitted, sets C<$\> to the current value of
604 C<$/>. For instance, to trim lines to 80 columns:
606 perl -lpe 'substr($_, 80) = ""'
608 Note that the assignment C<$\ = $/> is done when the switch is processed,
609 so the input record separator can be different than the output record
610 separator if the B<-l> switch is followed by a B<-0> switch:
612 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
614 This sets C<$\> to newline and then sets C<$/> to the null character.
616 =item B<-m>[B<->]I<module>
619 =item B<-M>[B<->]I<module>
621 =item B<-M>[B<->]I<'module ...'>
623 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
625 B<-m>I<module> executes C<use> I<module> C<();> before executing your
628 B<-M>I<module> executes C<use> I<module> C<;> before executing your
629 program. You can use quotes to add extra code after the module name,
630 e.g., C<'-Mmodule qw(foo bar)'>.
632 If the first character after the B<-M> or B<-m> is a dash (C<->)
633 then the 'use' is replaced with 'no'.
635 A little builtin syntactic sugar means you can also say
636 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
637 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
638 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
639 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
640 removes the distinction between B<-m> and B<-M>.
642 A consequence of this is that B<-MFoo=number> never does a version check
643 (unless C<Foo::import()> itself is set up to do a version check, which
644 could happen for example if Foo inherits from Exporter.)
649 causes Perl to assume the following loop around your program, which
650 makes it iterate over filename arguments somewhat like B<sed -n> or
655 ... # your program goes here
658 Note that the lines are not printed by default. See B<-p> to have
659 lines printed. If a file named by an argument cannot be opened for
660 some reason, Perl warns you about it and moves on to the next file.
662 Here is an efficient way to delete all files that haven't been modified for
665 find . -mtime +7 -print | perl -nle unlink
667 This is faster than using the B<-exec> switch of B<find> because you don't
668 have to start a process on every filename found. It does suffer from
669 the bug of mishandling newlines in pathnames, which you can fix if
670 you follow the example under B<-0>.
672 C<BEGIN> and C<END> blocks may be used to capture control before or after
673 the implicit program loop, just as in B<awk>.
678 causes Perl to assume the following loop around your program, which
679 makes it iterate over filename arguments somewhat like B<sed>:
684 ... # your program goes here
686 print or die "-p destination: $!\n";
689 If a file named by an argument cannot be opened for some reason, Perl
690 warns you about it, and moves on to the next file. Note that the
691 lines are printed automatically. An error occurring during printing is
692 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
693 overrides a B<-n> switch.
695 C<BEGIN> and C<END> blocks may be used to capture control before or after
696 the implicit loop, just as in B<awk>.
701 B<NOTE: Use of -P is strongly discouraged because of its inherent
702 problems, including poor portability. It is deprecated and will be
703 removed in a future version of Perl.>
705 This option causes your program to be run through the C preprocessor before
706 compilation by Perl. Because both comments and B<cpp> directives begin
707 with the # character, you should avoid starting comments with any words
708 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
710 If you're considering using C<-P>, you might also want to look at the
711 Filter::cpp module from CPAN.
713 The problems of -P include, but are not limited to:
719 The C<#!> line is stripped, so any switches there don't apply.
723 A C<-P> on a C<#!> line doesn't work.
727 B<All> lines that begin with (whitespace and) a C<#> but
728 do not look like cpp commands, are stripped, including anything
729 inside Perl strings, regular expressions, and here-docs .
733 In some platforms the C preprocessor knows too much: it knows about
734 the C++ -style until-end-of-line comments starting with C<"//">.
735 This will cause problems with common Perl constructs like
739 because after -P this will became illegal code
743 The workaround is to use some other quoting separator than C<"/">,
744 like for example C<"!">:
752 It requires not only a working C preprocessor but also a working
753 F<sed>. If not on UNIX, you are probably out of luck on this.
757 Script line numbers are not preserved.
761 The C<-x> does not work with C<-P>.
768 enables rudimentary switch parsing for switches on the command
769 line after the program name but before any filename arguments (or before
770 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
771 corresponding variable in the Perl program. The following program
772 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
773 if it is invoked with B<-xyz=abc>.
776 if ($xyz) { print "$xyz\n" }
778 Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
779 with C<strict refs>. Also, when using this option on a script with
780 warnings enabled you may get a lot of spurious "used only once" warnings.
785 makes Perl use the PATH environment variable to search for the
786 program (unless the name of the program contains directory separators).
788 On some platforms, this also makes Perl append suffixes to the
789 filename while searching for it. For example, on Win32 platforms,
790 the ".bat" and ".cmd" suffixes are appended if a lookup for the
791 original name fails, and if the name does not already end in one
792 of those suffixes. If your Perl was compiled with DEBUGGING turned
793 on, using the -Dp switch to Perl shows how the search progresses.
795 Typically this is used to emulate #! startup on platforms that don't
796 support #!. Its also convenient when debugging a script that uses #!,
797 and is thus normally found by the shell's $PATH search mechanism.
799 This example works on many platforms that have a shell compatible with
803 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
804 if $running_under_some_shell;
806 The system ignores the first line and feeds the program to F</bin/sh>,
807 which proceeds to try to execute the Perl program as a shell script.
808 The shell executes the second line as a normal shell command, and thus
809 starts up the Perl interpreter. On some systems $0 doesn't always
810 contain the full pathname, so the B<-S> tells Perl to search for the
811 program if necessary. After Perl locates the program, it parses the
812 lines and ignores them because the variable $running_under_some_shell
813 is never true. If the program will be interpreted by csh, you will need
814 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
815 embedded spaces (and such) in the argument list. To start up sh rather
816 than csh, some systems may have to replace the #! line with a line
817 containing just a colon, which will be politely ignored by Perl. Other
818 systems can't control that, and need a totally devious construct that
819 will work under any of B<csh>, B<sh>, or Perl, such as the following:
821 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
822 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
823 if $running_under_some_shell;
825 If the filename supplied contains directory separators (i.e., is an
826 absolute or relative pathname), and if that file is not found,
827 platforms that append file extensions will do so and try to look
828 for the file with those extensions added, one by one.
830 On DOS-like platforms, if the program does not contain directory
831 separators, it will first be searched for in the current directory
832 before being searched for on the PATH. On Unix platforms, the
833 program will be searched for strictly on the PATH.
838 Like B<-T>, but taint checks will issue warnings rather than fatal
839 errors. These warnings can be controlled normally with C<no warnings
842 B<NOTE: this is not a substitute for -T.> This is meant only to be
843 used as a temporary development aid while securing legacy code:
844 for real production code and for new secure code written from scratch
845 always use the real B<-T>.
850 forces "taint" checks to be turned on so you can test them. Ordinarily
851 these checks are done only when running setuid or setgid. It's a
852 good idea to turn them on explicitly for programs that run on behalf
853 of someone else whom you might not necessarily trust, such as CGI
854 programs or any internet servers you might write in Perl. See
855 L<perlsec> for details. For security reasons, this option must be
856 seen by Perl quite early; usually this means it must appear early
857 on the command line or in the #! line for systems which support
863 This obsolete switch causes Perl to dump core after compiling your
864 program. You can then in theory take this core dump and turn it
865 into an executable file by using the B<undump> program (not supplied).
866 This speeds startup at the expense of some disk space (which you
867 can minimize by stripping the executable). (Still, a "hello world"
868 executable comes out to about 200K on my machine.) If you want to
869 execute a portion of your program before dumping, use the dump()
870 operator instead. Note: availability of B<undump> is platform
871 specific and may not be available for a specific port of Perl.
876 allows Perl to do unsafe operations. Currently the only "unsafe"
877 operations are attempting to unlink directories while running as
878 superuser, and running setuid programs with fatal taint checks turned
879 into warnings. Note that the B<-w> switch (or the C<$^W> variable)
880 must be used along with this option to actually I<generate> the
881 taint-check warnings.
886 prints the version and patchlevel of your perl executable.
891 prints summary of the major perl configuration values and the current
894 =item B<-V:>I<configvar>
896 Prints to STDOUT the value of the named configuration variable(s),
897 with multiples when your configvar argument looks like a regex (has
898 non-letters). For example:
901 libc='/lib/libc-2.2.4.so';
903 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
904 libc='/lib/libc-2.2.4.so';
906 libpth='/usr/local/lib /lib /usr/lib';
907 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
909 libc='/lib/libc-2.2.4.so';
913 Additionally, extra colons can be used to control formatting. A
914 trailing colon suppresses the linefeed and terminator ';', allowing
915 you to embed queries into shell commands. (mnemonic: PATH separator
918 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
919 compression-vars: zcat='' zip='zip' are here !
921 A leading colon removes the 'name=' part of the response, this allows
922 you to map to the name you need. (mnemonic: empty label)
924 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
927 Leading and trailing colons can be used together if you need
928 positional parameter values without the names. Note that in the case
929 below, the PERL_API params are returned in alphabetical order.
931 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
932 building_on 'linux' '5' '1' '9' now
937 prints warnings about dubious constructs, such as variable names
938 that are mentioned only once and scalar variables that are used
939 before being set, redefined subroutines, references to undefined
940 filehandles or filehandles opened read-only that you are attempting
941 to write on, values used as a number that don't look like numbers,
942 using an array as though it were a scalar, if your subroutines
943 recurse more than 100 deep, and innumerable other things.
945 This switch really just enables the internal C<$^W> variable. You
946 can disable or promote into fatal errors specific warnings using
947 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
948 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
949 facility is also available if you want to manipulate entire classes
950 of warnings; see L<warnings> or L<perllexwarn>.
955 Enables all warnings regardless of C<no warnings> or C<$^W>.
961 Disables all warnings regardless of C<use warnings> or C<$^W>.
967 =item B<-x>I<directory>
969 tells Perl that the program is embedded in a larger chunk of unrelated
970 ASCII text, such as in a mail message. Leading garbage will be
971 discarded until the first line that starts with #! and contains the
972 string "perl". Any meaningful switches on that line will be applied.
973 If a directory name is specified, Perl will switch to that directory
974 before running the program. The B<-x> switch controls only the
975 disposal of leading garbage. The program must be terminated with
976 C<__END__> if there is trailing garbage to be ignored (the program
977 can process any or all of the trailing garbage via the DATA filehandle
980 The directory, if specified, must appear immedately following the B<-x>
981 with no intervening whitespace.
986 X<perl, environment variables>
993 Used if chdir has no argument.
998 Used if chdir has no argument and HOME is not set.
1003 Used in executing subprocesses, and in finding the program if B<-S> is
1009 A list of directories in which to look for Perl library
1010 files before looking in the standard library and the current
1011 directory. Any architecture-specific directories under the specified
1012 locations are automatically included if they exist (this lookup
1013 being done at interpreter startup time.)
1015 If PERL5LIB is not defined, PERLLIB is used. Directories are separated
1016 (like in PATH) by a colon on unixish platforms and by a semicolon on
1017 Windows (the proper path separator being given by the command C<perl
1020 When running taint checks (either because the program was running setuid
1021 or setgid, or the B<-T> or B<-t> switch was specified), neither variable
1022 is used. The program should instead say:
1024 use lib "/my/directory";
1029 Command-line options (switches). Switches in this variable are taken
1030 as if they were on every Perl command line. Only the B<-[CDIMUdmtwA]>
1031 switches are allowed. When running taint checks (because the program
1032 was running setuid or setgid, or the B<-T> switch was used), this
1033 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
1034 enabled, and any subsequent options ignored.
1039 A space (or colon) separated list of PerlIO layers. If perl is built
1040 to use PerlIO system for IO (the default) these layers effect perl's IO.
1042 It is conventional to start layer names with a colon e.g. C<:perlio> to
1043 emphasise their similarity to variable "attributes". But the code that parses
1044 layer specification strings (which is also used to decode the PERLIO
1045 environment variable) treats the colon as a separator.
1047 An unset or empty PERLIO is equivalent to the default set of layers for
1048 your platform, for example C<:unix:perlio> on UNIX-like systems
1049 and C<:unix:crlf> on Windows and other DOS-like systems.
1051 The list becomes the default for I<all> perl's IO. Consequently only built-in
1052 layers can appear in this list, as external layers (such as :encoding()) need
1053 IO in order to load them!. See L<"open pragma"|open> for how to add external
1054 encodings as defaults.
1056 The layers that it makes sense to include in the PERLIO environment
1057 variable are briefly summarised below. For more details see L<PerlIO>.
1064 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
1065 Unlikely to be useful on its own in the global PERLIO environment variable.
1066 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1071 A layer which does CRLF to "\n" translation distinguishing "text" and
1072 "binary" files in the manner of MS-DOS and similar operating systems.
1073 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1074 as being an end-of-file marker.)
1079 A layer which implements "reading" of files by using C<mmap()> to
1080 make (whole) file appear in the process's address space, and then
1081 using that as PerlIO's "buffer".
1086 This is a re-implementation of "stdio-like" buffering written as a
1087 PerlIO "layer". As such it will call whatever layer is below it for
1088 its operations (typically C<:unix>).
1093 An experimental pseudolayer that removes the topmost layer.
1094 Use with the same care as is reserved for nitroglycerin.
1099 A pseudolayer that manipulates other layers. Applying the C<:raw>
1100 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1101 pass each byte as-is without any translation. In particular CRLF
1102 translation, and/or :utf8 intuited from locale are disabled.
1104 Unlike in the earlier versions of Perl C<:raw> is I<not>
1105 just the inverse of C<:crlf> - other layers which would affect the
1106 binary nature of the stream are also removed or disabled.
1111 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1112 library calls. The layer provides both buffering and IO.
1113 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1114 is platforms normal behaviour. You will need a C<:crlf> layer above it
1120 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1125 A pseudolayer that turns on a flag on the layer below to tell perl
1126 that output should be in utf8 and that input should be regarded as
1127 already in utf8 form. May be useful in PERLIO environment
1128 variable to make UTF-8 the default. (To turn off that behaviour
1129 use C<:bytes> layer.)
1134 On Win32 platforms this I<experimental> layer uses native "handle" IO
1135 rather than unix-like numeric file descriptor layer. Known to be
1136 buggy in this release.
1140 On all platforms the default set of layers should give acceptable results.
1142 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1143 Configure is setup to prefer "stdio" implementation if system's library
1144 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1147 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1148 has a number of bugs/mis-features for perl IO which are somewhat
1149 C compiler vendor/version dependent. Using our own C<crlf> layer as
1150 the buffer avoids those issues and makes things more uniform.
1151 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1154 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1155 compiler's numeric file descriptor routines. There is an experimental native
1156 C<win32> layer which is expected to be enhanced and should eventually be
1157 the default under Win32.
1162 If set to the name of a file or device then certain operations of PerlIO
1163 sub-system will be logged to that file (opened as append). Typical uses
1166 PERLIO_DEBUG=/dev/tty perl script ...
1168 and Win32 approximate equivalent:
1170 set PERLIO_DEBUG=CON
1173 This functionality is disabled for setuid scripts and for scripts run
1179 A list of directories in which to look for Perl library
1180 files before looking in the standard library and the current directory.
1181 If PERL5LIB is defined, PERLLIB is not used.
1186 The command used to load the debugger code. The default is:
1188 BEGIN { require 'perl5db.pl' }
1190 =item PERL5DB_THREADED
1193 If set to a true value, indicates to the debugger that the code being
1194 debugged uses threads.
1196 =item PERL5SHELL (specific to the Win32 port)
1199 May be set to an alternative shell that perl must use internally for
1200 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1201 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1202 to be space-separated. Precede any character that needs to be protected
1203 (like a space or backslash) with a backslash.
1205 Note that Perl doesn't use COMSPEC for this purpose because
1206 COMSPEC has a high degree of variability among users, leading to
1207 portability concerns. Besides, perl can use a shell that may not be
1208 fit for interactive use, and setting COMSPEC to such a shell may
1209 interfere with the proper functioning of other programs (which usually
1210 look in COMSPEC to find a shell fit for interactive use).
1212 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1213 X<PERL_ALLOW_NON_IFS_LSP>
1215 Set to 1 to allow the use of non-IFS compatible LSP's.
1216 Perl normally searches for an IFS-compatible LSP because this is required
1217 for its emulation of Windows sockets as real filehandles. However, this may
1218 cause problems if you have a firewall such as McAfee Guardian which requires
1219 all applications to use its LSP which is not IFS-compatible, because clearly
1220 Perl will normally avoid using such an LSP.
1221 Setting this environment variable to 1 means that Perl will simply use the
1222 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1223 happy (and in that particular case Perl still works too because McAfee
1224 Guardian's LSP actually plays some other games which allow applications
1225 requiring IFS compatibility to work).
1227 =item PERL_DEBUG_MSTATS
1228 X<PERL_DEBUG_MSTATS>
1230 Relevant only if perl is compiled with the malloc included with the perl
1231 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1232 If set, this causes memory statistics to be dumped after execution. If set
1233 to an integer greater than one, also causes memory statistics to be dumped
1236 =item PERL_DESTRUCT_LEVEL
1237 X<PERL_DESTRUCT_LEVEL>
1239 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1240 this controls the behavior of global destruction of objects and other
1241 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1243 =item PERL_DL_NONLAZY
1246 Set to one to have perl resolve B<all> undefined symbols when it loads
1247 a dynamic library. The default behaviour is to resolve symbols when
1248 they are used. Setting this variable is useful during testing of
1249 extensions as it ensures that you get an error on misspelled function
1250 names even if the test suite doesn't call it.
1255 If using the C<encoding> pragma without an explicit encoding name, the
1256 PERL_ENCODING environment variable is consulted for an encoding name.
1258 =item PERL_HASH_SEED
1261 (Since Perl 5.8.1.) Used to randomise perl's internal hash function.
1262 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1263 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1264 things, that hash keys will always have the same ordering between
1265 different runs of perl.
1267 Most hashes return elements in the same order as Perl 5.8.0 by default.
1268 On a hash by hash basis, if pathological data is detected during a hash
1269 key insertion, then that hash will switch to an alternative random hash
1272 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1273 If perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1274 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1276 If PERL_HASH_SEED is unset or set to a non-numeric string, perl uses
1277 the pseudorandom seed supplied by the operating system and libraries.
1279 B<Please note that the hash seed is sensitive information>. Hashes are
1280 randomized to protect against local and remote attacks against Perl
1281 code. By manually setting a seed this protection may be partially or
1284 See L<perlsec/"Algorithmic Complexity Attacks"> and
1285 L</PERL_HASH_SEED_DEBUG> for more information.
1287 =item PERL_HASH_SEED_DEBUG
1288 X<PERL_HASH_SEED_DEBUG>
1290 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1291 the hash seed at the beginning of execution. This, combined with
1292 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1293 behavior caused by hash randomization.
1295 B<Note that the hash seed is sensitive information>: by knowing it one
1296 can craft a denial-of-service attack against Perl code, even remotely,
1297 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1298 B<Do not disclose the hash seed> to people who don't need to know it.
1299 See also hash_seed() of L<Hash::Util>.
1301 =item PERL_ROOT (specific to the VMS port)
1304 A translation concealed rooted logical name that contains perl and the
1305 logical device for the @INC path on VMS only. Other logical names that
1306 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1307 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1308 L<perlvms> and in F<README.vms> in the Perl source distribution.
1313 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1314 signals behaviour (immediate but unsafe) is restored. If set to
1315 C<safe> the safe (or deferred) signals are used.
1316 See L<perlipc/"Deferred Signals (Safe Signals)">.
1321 Equivalent to the B<-C> command-line switch. Note that this is not
1322 a boolean variable-- setting this to C<"1"> is not the right way to
1323 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1324 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1325 your shell before starting Perl). See the description of the C<-C>
1326 switch for more information.
1328 =item SYS$LOGIN (specific to the VMS port)
1331 Used if chdir has no argument and HOME and LOGDIR are not set.
1335 Perl also has environment variables that control how Perl handles data
1336 specific to particular natural languages. See L<perllocale>.
1338 Apart from these, Perl uses no other environment variables, except
1339 to make them available to the program being executed, and to child
1340 processes. However, programs running setuid would do well to execute
1341 the following lines before doing anything else, just to keep people
1344 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1345 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1346 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};