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>] >]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ B<-eE> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
20 The normal way to run a Perl program is by making it directly
21 executable, or else by passing the name of the source file as an
22 argument on the command line. (An interactive Perl environment
23 is also possible--see L<perldebug> for details on how to do that.)
24 Upon startup, Perl looks for your program in one of the following
31 Specified line by line via B<-e> or B<-E> switches on the command line.
35 Contained in the file specified by the first filename on the command line.
36 (Note that systems supporting the #! notation invoke interpreters this
37 way. See L<Location of Perl>.)
41 Passed in implicitly via standard input. This works only if there are
42 no filename arguments--to pass arguments to a STDIN-read program you
43 must explicitly specify a "-" for the program name.
47 With methods 2 and 3, Perl starts parsing the input file from the
48 beginning, unless you've specified a B<-x> switch, in which case it
49 scans for the first line starting with #! and containing the word
50 "perl", and starts there instead. This is useful for running a program
51 embedded in a larger message. (In this case you would indicate the end
52 of the program using the C<__END__> token.)
54 The #! line is always examined for switches as the line is being
55 parsed. Thus, if you're on a machine that allows only one argument
56 with the #! line, or worse, doesn't even recognize the #! line, you
57 still can get consistent switch behavior regardless of how Perl was
58 invoked, even if B<-x> was used to find the beginning of the program.
60 Because historically some operating systems silently chopped off
61 kernel interpretation of the #! line after 32 characters, some
62 switches may be passed in on the command line, and some may not;
63 you could even get a "-" without its letter, if you're not careful.
64 You probably want to make sure that all your switches fall either
65 before or after that 32-character boundary. Most switches don't
66 actually care if they're processed redundantly, but getting a "-"
67 instead of a complete switch could cause Perl to try to execute
68 standard input instead of your program. And a partial B<-I> switch
69 could also cause odd results.
71 Some switches do care if they are processed twice, for instance
72 combinations of B<-l> and B<-0>. Either put all the switches after
73 the 32-character boundary (if applicable), or replace the use of
74 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
76 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
77 The sequences "-*" and "- " are specifically ignored so that you could,
78 if you were so inclined, say
80 #!/bin/sh -- # -*- perl -*- -p
81 eval 'exec perl -wS $0 ${1+"$@"}'
82 if $running_under_some_shell;
84 to let Perl see the B<-p> switch.
86 A similar trick involves the B<env> program, if you have it.
90 The examples above use a relative path to the perl interpreter,
91 getting whatever version is first in the user's path. If you want
92 a specific version of Perl, say, perl5.005_57, you should place
93 that directly in the #! line's path.
95 If the #! line does not contain the word "perl", the program named after
96 the #! is executed instead of the Perl interpreter. This is slightly
97 bizarre, but it helps people on machines that don't do #!, because they
98 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
99 dispatch the program to the correct interpreter for them.
101 After locating your program, Perl compiles the entire program to an
102 internal form. If there are any compilation errors, execution of the
103 program is not attempted. (This is unlike the typical shell script,
104 which might run part-way through before finding a syntax error.)
106 If the program is syntactically correct, it is executed. If the program
107 runs off the end without hitting an exit() or die() operator, an implicit
108 C<exit(0)> is provided to indicate successful completion.
110 =head2 #! and quoting on non-Unix systems
113 Unix's #! technique can be simulated on other systems:
121 extproc perl -S -your_switches
123 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
128 Create a batch file to run your program, and codify it in
129 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
130 distribution for more information).
134 The Win95/NT installation, when using the ActiveState installer for Perl,
135 will modify the Registry to associate the F<.pl> extension with the perl
136 interpreter. If you install Perl by other means (including building from
137 the sources), you may have to modify the Registry yourself. Note that
138 this means you can no longer tell the difference between an executable
139 Perl program and a Perl library file.
143 Under "Classic" MacOS, a perl program will have the appropriate Creator and
144 Type, so that double-clicking them will invoke the MacPerl application.
145 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
146 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
152 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
153 $ exit++ + ++$status != 0 and $exit = $status = undef;
155 at the top of your program, where B<-mysw> are any command line switches you
156 want to pass to Perl. You can now invoke the program directly, by saying
157 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
158 via F<DCL$PATH> by just using the name of the program).
160 This incantation is a bit much to remember, but Perl will display it for
161 you if you say C<perl "-V:startperl">.
165 Command-interpreters on non-Unix systems have rather different ideas
166 on quoting than Unix shells. You'll need to learn the special
167 characters in your command-interpreter (C<*>, C<\> and C<"> are
168 common) and how to protect whitespace and these characters to run
169 one-liners (see B<-e> below).
171 On some systems, you may have to change single-quotes to double ones,
172 which you must I<not> do on Unix or Plan 9 systems. You might also
173 have to change a single % to a %%.
178 perl -e 'print "Hello world\n"'
181 perl -e "print \"Hello world\n\""
184 print "Hello world\n"
185 (then Run "Myscript" or Shift-Command-R)
188 perl -e "print ""Hello world\n"""
190 The problem is that none of this is reliable: it depends on the
191 command and it is entirely possible neither works. If B<4DOS> were
192 the command shell, this would probably work better:
194 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
196 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
197 when nobody was looking, but just try to find documentation for its
200 Under the Macintosh, it depends which environment you are using. The MacPerl
201 shell, or MPW, is much like Unix shells in its support for several
202 quoting variants, except that it makes free use of the Macintosh's non-ASCII
203 characters as control characters.
205 There is no general solution to all of this. It's just a mess.
207 =head2 Location of Perl
208 X<perl, location of interpreter>
210 It may seem obvious to say, but Perl is useful only when users can
211 easily find it. When possible, it's good for both F</usr/bin/perl>
212 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
213 that can't be done, system administrators are strongly encouraged
214 to put (symlinks to) perl and its accompanying utilities into a
215 directory typically found along a user's PATH, or in some other
216 obvious and convenient place.
218 In this documentation, C<#!/usr/bin/perl> on the first line of the program
219 will stand in for whatever method works on your system. You are
220 advised to use a specific path if you care about a specific version.
222 #!/usr/local/bin/perl5.00554
224 or if you just want to be running at least version, place a statement
225 like this at the top of your program:
229 =head2 Command Switches
230 X<perl, command switches> X<command switches>
232 As with all standard commands, a single-character switch may be
233 clustered with the following switch, if any.
235 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
241 =item B<-0>[I<octal/hexadecimal>]
244 specifies the input record separator (C<$/>) as an octal or
245 hexadecimal number. If there are no digits, the null character is the
246 separator. Other switches may precede or follow the digits. For
247 example, if you have a version of B<find> which can print filenames
248 terminated by the null character, you can say this:
250 find . -name '*.orig' -print0 | perl -n0e unlink
252 The special value 00 will cause Perl to slurp files in paragraph mode.
253 The value 0777 will cause Perl to slurp files whole because there is no
254 legal byte with that value.
256 If you want to specify any Unicode character, use the hexadecimal
257 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
258 (This means that you cannot use the C<-x> with a directory name that
259 consists of hexadecimal digits.)
264 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
265 split command to the @F array is done as the first thing inside the
266 implicit while loop produced by the B<-n> or B<-p>.
268 perl -ane 'print pop(@F), "\n";'
277 An alternate delimiter may be specified using B<-F>.
279 =item B<-C [I<number/list>]>
282 The C<-C> flag controls some of the Perl Unicode features.
284 As of 5.8.1, the C<-C> can be followed either by a number or a list
285 of option letters. The letters, their numeric values, and effects
286 are as follows; listing the letters is equal to summing the numbers.
288 I 1 STDIN is assumed to be in UTF-8
289 O 2 STDOUT will be in UTF-8
290 E 4 STDERR will be in UTF-8
292 i 8 UTF-8 is the default PerlIO layer for input streams
293 o 16 UTF-8 is the default PerlIO layer for output streams
295 A 32 the @ARGV elements are expected to be strings encoded
297 L 64 normally the "IOEioA" are unconditional,
298 the L makes them conditional on the locale environment
299 variables (the LC_ALL, LC_TYPE, and LANG, in the order
300 of decreasing precedence) -- if the variables indicate
301 UTF-8, then the selected "IOEioA" are in effect
302 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching code in
305 =for documenting_the_underdocumented
306 perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
309 perltodo mentions Unicode in %ENV and filenames. I guess that these will be
310 options e and f (or F).
312 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
313 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
316 The C<io> options mean that any subsequent open() (or similar I/O
317 operations) will have the C<:utf8> PerlIO layer implicitly applied
318 to them, in other words, UTF-8 is expected from any input stream,
319 and UTF-8 is produced to any output stream. This is just the default,
320 with explicit layers in open() and with binmode() one can manipulate
323 C<-C> on its own (not followed by any number or option list), or the
324 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
325 same effect as C<-CSDL>. In other words, the standard I/O handles and
326 the default C<open()> layer are UTF-8-fied B<but> only if the locale
327 environment variables indicate a UTF-8 locale. This behaviour follows
328 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
330 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
331 disable all the above Unicode features.
333 The read-only magic variable C<${^UNICODE}> reflects the numeric value
334 of this setting. This is variable is set during Perl startup and is
335 thereafter read-only. If you want runtime effects, use the three-arg
336 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
337 and the C<open> pragma (see L<open>).
339 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
340 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
341 This feature was practically unused, however, and the command line
342 switch was therefore "recycled".)
347 causes Perl to check the syntax of the program and then exit without
348 executing it. Actually, it I<will> execute C<BEGIN>, C<UNITCHECK>,
349 C<CHECK>, and C<use> blocks, because these are considered as occurring
350 outside the execution of your program. C<INIT> and C<END> blocks,
351 however, will be skipped.
358 runs the program under the Perl debugger. See L<perldebug>.
359 If B<t> is specified, it indicates to the debugger that threads
360 will be used in the code being debugged.
362 =item B<-d:>I<foo[=bar,baz]>
365 =item B<-dt:>I<foo[=bar,baz]>
367 runs the program under the control of a debugging, profiling, or
368 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
369 the program using the Devel::DProf profiler. As with the B<-M>
370 flag, options may be passed to the Devel::foo package where they
371 will be received and interpreted by the Devel::foo::import routine.
372 The comma-separated list of options must follow a C<=> character.
373 If B<t> is specified, it indicates to the debugger that threads
374 will be used in the code being debugged.
377 =item B<-D>I<letters>
378 X<-D> X<DEBUGGING> X<-DDEBUGGING>
382 sets debugging flags. To watch how it executes your program, use
383 B<-Dtls>. (This works only if debugging is compiled into your
384 Perl.) Another nice value is B<-Dx>, which lists your compiled
385 syntax tree. And B<-Dr> displays compiled regular expressions;
386 the format of the output is explained in L<perldebguts>.
388 As an alternative, specify a number instead of list of letters (e.g.,
389 B<-D14> is equivalent to B<-Dtls>):
391 1 p Tokenizing and parsing (with v, displays parse stack)
392 2 s Stack snapshots (with v, displays all stacks)
393 4 l Context (loop) stack processing
395 16 o Method and overloading resolution
396 32 c String/numeric conversions
397 64 P Print profiling info, source file input state
398 128 m Memory allocation
399 256 f Format processing
400 512 r Regular expression parsing and execution
401 1024 x Syntax tree dump
402 2048 u Tainting checks
403 4096 U Unofficial, User hacking (reserved for private, unreleased use)
404 8192 H Hash dump -- usurps values()
405 16384 X Scratchpad allocation
407 65536 S Thread synchronization
409 262144 R Include reference counts of dumped variables (eg when using -Ds)
410 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
411 1048576 v Verbose: use in conjunction with other flags
412 2097152 C Copy On Write
413 4194304 A Consistency checks on internal structures
414 8388608 q quiet - currently only suppresses the "EXECUTING" message
416 All these flags require B<-DDEBUGGING> when you compile the Perl
417 executable (but see L<Devel::Peek>, L<re> which may change this).
418 See the F<INSTALL> file in the Perl source distribution
419 for how to do this. This flag is automatically set if you include B<-g>
420 option when C<Configure> asks you about optimizer/debugger flags.
422 If you're just trying to get a print out of each line of Perl code
423 as it executes, the way that C<sh -x> provides for shell scripts,
424 you can't use Perl's B<-D> switch. Instead do this
426 # If you have "env" utility
427 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
429 # Bourne shell syntax
430 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
433 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
435 See L<perldebug> for details and variations.
437 =item B<-e> I<commandline>
440 may be used to enter one line of program. If B<-e> is given, Perl
441 will not look for a filename in the argument list. Multiple B<-e>
442 commands may be given to build up a multi-line script. Make sure
443 to use semicolons where you would in a normal program.
445 =item B<-E> I<commandline>
448 behaves just like B<-e>, except that it implicitly enables all
449 optional features (in the main compilation unit). See L<feature>.
454 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
456 Perl can be built so that it by default will try to execute
457 F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block).
458 This is a hook that allows the sysadmin to customize how perl behaves.
459 It can for instance be used to add entries to the @INC array to make perl
460 find modules in non-standard locations.
462 =item B<-F>I<pattern>
465 specifies the pattern to split on if B<-a> is also in effect. The
466 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
467 put in single quotes. You can't use literal whitespace in the pattern.
472 prints a summary of the options.
474 =item B<-i>[I<extension>]
477 specifies that files processed by the C<E<lt>E<gt>> construct are to be
478 edited in-place. It does this by renaming the input file, opening the
479 output file by the original name, and selecting that output file as the
480 default for print() statements. The extension, if supplied, is used to
481 modify the name of the old file to make a backup copy, following these
484 If no extension is supplied, no backup is made and the current file is
487 If the extension doesn't contain a C<*>, then it is appended to the
488 end of the current filename as a suffix. If the extension does
489 contain one or more C<*> characters, then each C<*> is replaced
490 with the current filename. In Perl terms, you could think of this
493 ($backup = $extension) =~ s/\*/$file_name/g;
495 This allows you to add a prefix to the backup file, instead of (or in
496 addition to) a suffix:
498 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
500 Or even to place backup copies of the original files into another
501 directory (provided the directory already exists):
503 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
505 These sets of one-liners are equivalent:
507 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
508 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
510 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
511 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
513 From the shell, saying
515 $ perl -p -i.orig -e "s/foo/bar/; ... "
517 is the same as using the program:
519 #!/usr/bin/perl -pi.orig
522 which is equivalent to
525 $extension = '.orig';
527 if ($ARGV ne $oldargv) {
528 if ($extension !~ /\*/) {
529 $backup = $ARGV . $extension;
532 ($backup = $extension) =~ s/\*/$ARGV/g;
534 rename($ARGV, $backup);
535 open(ARGVOUT, ">$ARGV");
542 print; # this prints to original filename
546 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
547 know when the filename has changed. It does, however, use ARGVOUT for
548 the selected filehandle. Note that STDOUT is restored as the default
549 output filehandle after the loop.
551 As shown above, Perl creates the backup file whether or not any output
552 is actually changed. So this is just a fancy way to copy files:
554 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
556 $ perl -p -i'.orig' -e 1 file1 file2 file3...
558 You can use C<eof> without parentheses to locate the end of each input
559 file, in case you want to append to each file, or reset line numbering
560 (see example in L<perlfunc/eof>).
562 If, for a given file, Perl is unable to create the backup file as
563 specified in the extension then it will skip that file and continue on
564 with the next one (if it exists).
566 For a discussion of issues surrounding file permissions and B<-i>,
567 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?>.
569 You cannot use B<-i> to create directories or to strip extensions from
572 Perl does not expand C<~> in filenames, which is good, since some
573 folks use it for their backup files:
575 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
577 Note that because B<-i> renames or deletes the original file before
578 creating a new file of the same name, UNIX-style soft and hard links will
581 Finally, the B<-i> switch does not impede execution when no
582 files are given on the command line. In this case, no backup is made
583 (the original file cannot, of course, be determined) and processing
584 proceeds from STDIN to STDOUT as might be expected.
586 =item B<-I>I<directory>
589 Directories specified by B<-I> are prepended to the search path for
592 =item B<-l>[I<octnum>]
595 enables automatic line-ending processing. It has two separate
596 effects. First, it automatically chomps C<$/> (the input record
597 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
598 (the output record separator) to have the value of I<octnum> so
599 that any print statements will have that separator added back on.
600 If I<octnum> is omitted, sets C<$\> to the current value of
601 C<$/>. For instance, to trim lines to 80 columns:
603 perl -lpe 'substr($_, 80) = ""'
605 Note that the assignment C<$\ = $/> is done when the switch is processed,
606 so the input record separator can be different than the output record
607 separator if the B<-l> switch is followed by a B<-0> switch:
609 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
611 This sets C<$\> to newline and then sets C<$/> to the null character.
613 =item B<-m>[B<->]I<module>
616 =item B<-M>[B<->]I<module>
618 =item B<-M>[B<->]I<'module ...'>
620 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
622 B<-m>I<module> executes C<use> I<module> C<();> before executing your
625 B<-M>I<module> executes C<use> I<module> C<;> before executing your
626 program. You can use quotes to add extra code after the module name,
627 e.g., C<'-Mmodule qw(foo bar)'>.
629 If the first character after the B<-M> or B<-m> is a dash (C<->)
630 then the 'use' is replaced with 'no'.
632 A little builtin syntactic sugar means you can also say
633 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
634 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
635 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
636 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
637 removes the distinction between B<-m> and B<-M>.
639 A consequence of this is that B<-MFoo=number> never does a version check
640 (unless C<Foo::import()> itself is set up to do a version check, which
641 could happen for example if Foo inherits from Exporter.)
646 causes Perl to assume the following loop around your program, which
647 makes it iterate over filename arguments somewhat like B<sed -n> or
652 ... # your program goes here
655 Note that the lines are not printed by default. See B<-p> to have
656 lines printed. If a file named by an argument cannot be opened for
657 some reason, Perl warns you about it and moves on to the next file.
659 Here is an efficient way to delete all files that haven't been modified for
662 find . -mtime +7 -print | perl -nle unlink
664 This is faster than using the B<-exec> switch of B<find> because you don't
665 have to start a process on every filename found. It does suffer from
666 the bug of mishandling newlines in pathnames, which you can fix if
667 you follow the example under B<-0>.
669 C<BEGIN> and C<END> blocks may be used to capture control before or after
670 the implicit program loop, just as in B<awk>.
675 causes Perl to assume the following loop around your program, which
676 makes it iterate over filename arguments somewhat like B<sed>:
681 ... # your program goes here
683 print or die "-p destination: $!\n";
686 If a file named by an argument cannot be opened for some reason, Perl
687 warns you about it, and moves on to the next file. Note that the
688 lines are printed automatically. An error occurring during printing is
689 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
690 overrides a B<-n> switch.
692 C<BEGIN> and C<END> blocks may be used to capture control before or after
693 the implicit loop, just as in B<awk>.
698 enables rudimentary switch parsing for switches on the command
699 line after the program name but before any filename arguments (or before
700 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
701 corresponding variable in the Perl program. The following program
702 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
703 if it is invoked with B<-xyz=abc>.
706 if ($xyz) { print "$xyz\n" }
708 Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
709 with C<strict refs>. Also, when using this option on a script with
710 warnings enabled you may get a lot of spurious "used only once" warnings.
715 makes Perl use the PATH environment variable to search for the
716 program (unless the name of the program contains directory separators).
718 On some platforms, this also makes Perl append suffixes to the
719 filename while searching for it. For example, on Win32 platforms,
720 the ".bat" and ".cmd" suffixes are appended if a lookup for the
721 original name fails, and if the name does not already end in one
722 of those suffixes. If your Perl was compiled with DEBUGGING turned
723 on, using the -Dp switch to Perl shows how the search progresses.
725 Typically this is used to emulate #! startup on platforms that don't
726 support #!. Its also convenient when debugging a script that uses #!,
727 and is thus normally found by the shell's $PATH search mechanism.
729 This example works on many platforms that have a shell compatible with
733 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
734 if $running_under_some_shell;
736 The system ignores the first line and feeds the program to F</bin/sh>,
737 which proceeds to try to execute the Perl program as a shell script.
738 The shell executes the second line as a normal shell command, and thus
739 starts up the Perl interpreter. On some systems $0 doesn't always
740 contain the full pathname, so the B<-S> tells Perl to search for the
741 program if necessary. After Perl locates the program, it parses the
742 lines and ignores them because the variable $running_under_some_shell
743 is never true. If the program will be interpreted by csh, you will need
744 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
745 embedded spaces (and such) in the argument list. To start up sh rather
746 than csh, some systems may have to replace the #! line with a line
747 containing just a colon, which will be politely ignored by Perl. Other
748 systems can't control that, and need a totally devious construct that
749 will work under any of B<csh>, B<sh>, or Perl, such as the following:
751 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
752 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
753 if $running_under_some_shell;
755 If the filename supplied contains directory separators (i.e., is an
756 absolute or relative pathname), and if that file is not found,
757 platforms that append file extensions will do so and try to look
758 for the file with those extensions added, one by one.
760 On DOS-like platforms, if the program does not contain directory
761 separators, it will first be searched for in the current directory
762 before being searched for on the PATH. On Unix platforms, the
763 program will be searched for strictly on the PATH.
768 Like B<-T>, but taint checks will issue warnings rather than fatal
769 errors. These warnings can be controlled normally with C<no warnings
772 B<NOTE: this is not a substitute for -T.> This is meant only to be
773 used as a temporary development aid while securing legacy code:
774 for real production code and for new secure code written from scratch
775 always use the real B<-T>.
780 forces "taint" checks to be turned on so you can test them. Ordinarily
781 these checks are done only when running setuid or setgid. It's a
782 good idea to turn them on explicitly for programs that run on behalf
783 of someone else whom you might not necessarily trust, such as CGI
784 programs or any internet servers you might write in Perl. See
785 L<perlsec> for details. For security reasons, this option must be
786 seen by Perl quite early; usually this means it must appear early
787 on the command line or in the #! line for systems which support
793 This obsolete switch causes Perl to dump core after compiling your
794 program. You can then in theory take this core dump and turn it
795 into an executable file by using the B<undump> program (not supplied).
796 This speeds startup at the expense of some disk space (which you
797 can minimize by stripping the executable). (Still, a "hello world"
798 executable comes out to about 200K on my machine.) If you want to
799 execute a portion of your program before dumping, use the dump()
800 operator instead. Note: availability of B<undump> is platform
801 specific and may not be available for a specific port of Perl.
806 allows Perl to do unsafe operations. Currently the only "unsafe"
807 operations are attempting to unlink directories while running as
808 superuser, and running setuid programs with fatal taint checks turned
809 into warnings. Note that the B<-w> switch (or the C<$^W> variable)
810 must be used along with this option to actually I<generate> the
811 taint-check warnings.
816 prints the version and patchlevel of your perl executable.
821 prints summary of the major perl configuration values and the current
824 =item B<-V:>I<configvar>
826 Prints to STDOUT the value of the named configuration variable(s),
827 with multiples when your configvar argument looks like a regex (has
828 non-letters). For example:
831 libc='/lib/libc-2.2.4.so';
833 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
834 libc='/lib/libc-2.2.4.so';
836 libpth='/usr/local/lib /lib /usr/lib';
837 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
839 libc='/lib/libc-2.2.4.so';
843 Additionally, extra colons can be used to control formatting. A
844 trailing colon suppresses the linefeed and terminator ';', allowing
845 you to embed queries into shell commands. (mnemonic: PATH separator
848 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
849 compression-vars: zcat='' zip='zip' are here !
851 A leading colon removes the 'name=' part of the response, this allows
852 you to map to the name you need. (mnemonic: empty label)
854 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
857 Leading and trailing colons can be used together if you need
858 positional parameter values without the names. Note that in the case
859 below, the PERL_API params are returned in alphabetical order.
861 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
862 building_on 'linux' '5' '1' '9' now
867 prints warnings about dubious constructs, such as variable names
868 that are mentioned only once and scalar variables that are used
869 before being set, redefined subroutines, references to undefined
870 filehandles or filehandles opened read-only that you are attempting
871 to write on, values used as a number that don't look like numbers,
872 using an array as though it were a scalar, if your subroutines
873 recurse more than 100 deep, and innumerable other things.
875 This switch really just enables the internal C<$^W> variable. You
876 can disable or promote into fatal errors specific warnings using
877 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
878 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
879 facility is also available if you want to manipulate entire classes
880 of warnings; see L<warnings> or L<perllexwarn>.
885 Enables all warnings regardless of C<no warnings> or C<$^W>.
891 Disables all warnings regardless of C<use warnings> or C<$^W>.
897 =item B<-x>I<directory>
899 tells Perl that the program is embedded in a larger chunk of unrelated
900 ASCII text, such as in a mail message. Leading garbage will be
901 discarded until the first line that starts with #! and contains the
902 string "perl". Any meaningful switches on that line will be applied.
903 If a directory name is specified, Perl will switch to that directory
904 before running the program. The B<-x> switch controls only the
905 disposal of leading garbage. The program must be terminated with
906 C<__END__> if there is trailing garbage to be ignored (the program
907 can process any or all of the trailing garbage via the DATA filehandle
910 The directory, if specified, must appear immediately following the B<-x>
911 with no intervening whitespace.
916 X<perl, environment variables>
923 Used if chdir has no argument.
928 Used if chdir has no argument and HOME is not set.
933 Used in executing subprocesses, and in finding the program if B<-S> is
939 A list of directories in which to look for Perl library
940 files before looking in the standard library and the current
941 directory. Any architecture-specific directories under the specified
942 locations are automatically included if they exist (this lookup
943 being done at interpreter startup time.)
945 If PERL5LIB is not defined, PERLLIB is used. Directories are separated
946 (like in PATH) by a colon on unixish platforms and by a semicolon on
947 Windows (the proper path separator being given by the command C<perl
950 When running taint checks (either because the program was running setuid
951 or setgid, or the B<-T> or B<-t> switch was specified), neither variable
952 is used. The program should instead say:
954 use lib "/my/directory";
959 Command-line options (switches). Switches in this variable are taken
960 as if they were on every Perl command line. Only the B<-[CDIMUdmtw]>
961 switches are allowed. When running taint checks (because the program
962 was running setuid or setgid, or the B<-T> switch was used), this
963 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
964 enabled, and any subsequent options ignored.
969 A space (or colon) separated list of PerlIO layers. If perl is built
970 to use PerlIO system for IO (the default) these layers effect perl's IO.
972 It is conventional to start layer names with a colon e.g. C<:perlio> to
973 emphasise their similarity to variable "attributes". But the code that parses
974 layer specification strings (which is also used to decode the PERLIO
975 environment variable) treats the colon as a separator.
977 An unset or empty PERLIO is equivalent to the default set of layers for
978 your platform, for example C<:unix:perlio> on UNIX-like systems
979 and C<:unix:crlf> on Windows and other DOS-like systems.
981 The list becomes the default for I<all> perl's IO. Consequently only built-in
982 layers can appear in this list, as external layers (such as :encoding()) need
983 IO in order to load them!. See L<"open pragma"|open> for how to add external
984 encodings as defaults.
986 The layers that it makes sense to include in the PERLIO environment
987 variable are briefly summarised below. For more details see L<PerlIO>.
994 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
995 Unlikely to be useful on its own in the global PERLIO environment variable.
996 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1001 A layer which does CRLF to "\n" translation distinguishing "text" and
1002 "binary" files in the manner of MS-DOS and similar operating systems.
1003 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1004 as being an end-of-file marker.)
1009 A layer which implements "reading" of files by using C<mmap()> to
1010 make (whole) file appear in the process's address space, and then
1011 using that as PerlIO's "buffer".
1016 This is a re-implementation of "stdio-like" buffering written as a
1017 PerlIO "layer". As such it will call whatever layer is below it for
1018 its operations (typically C<:unix>).
1023 An experimental pseudolayer that removes the topmost layer.
1024 Use with the same care as is reserved for nitroglycerin.
1029 A pseudolayer that manipulates other layers. Applying the C<:raw>
1030 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1031 pass each byte as-is without any translation. In particular CRLF
1032 translation, and/or :utf8 intuited from locale are disabled.
1034 Unlike in the earlier versions of Perl C<:raw> is I<not>
1035 just the inverse of C<:crlf> - other layers which would affect the
1036 binary nature of the stream are also removed or disabled.
1041 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1042 library calls. The layer provides both buffering and IO.
1043 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1044 is platforms normal behaviour. You will need a C<:crlf> layer above it
1050 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1055 A pseudolayer that turns on a flag on the layer below to tell perl
1056 that output should be in utf8 and that input should be regarded as
1057 already in valid utf8 form. It does not check for validity and as such
1058 should be handled with caution for input. Generally C<:encoding(utf8)> is
1059 the best option when reading UTF-8 encoded data.
1064 On Win32 platforms this I<experimental> layer uses native "handle" IO
1065 rather than unix-like numeric file descriptor layer. Known to be
1066 buggy in this release.
1070 On all platforms the default set of layers should give acceptable results.
1072 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1073 Configure is setup to prefer "stdio" implementation if system's library
1074 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1077 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1078 has a number of bugs/mis-features for perl IO which are somewhat
1079 C compiler vendor/version dependent. Using our own C<crlf> layer as
1080 the buffer avoids those issues and makes things more uniform.
1081 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1084 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1085 compiler's numeric file descriptor routines. There is an experimental native
1086 C<win32> layer which is expected to be enhanced and should eventually be
1087 the default under Win32.
1092 If set to the name of a file or device then certain operations of PerlIO
1093 sub-system will be logged to that file (opened as append). Typical uses
1096 PERLIO_DEBUG=/dev/tty perl script ...
1098 and Win32 approximate equivalent:
1100 set PERLIO_DEBUG=CON
1103 This functionality is disabled for setuid scripts and for scripts run
1109 A list of directories in which to look for Perl library
1110 files before looking in the standard library and the current directory.
1111 If PERL5LIB is defined, PERLLIB is not used.
1116 The command used to load the debugger code. The default is:
1118 BEGIN { require 'perl5db.pl' }
1120 =item PERL5DB_THREADED
1123 If set to a true value, indicates to the debugger that the code being
1124 debugged uses threads.
1126 =item PERL5SHELL (specific to the Win32 port)
1129 May be set to an alternative shell that perl must use internally for
1130 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1131 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1132 to be space-separated. Precede any character that needs to be protected
1133 (like a space or backslash) with a backslash.
1135 Note that Perl doesn't use COMSPEC for this purpose because
1136 COMSPEC has a high degree of variability among users, leading to
1137 portability concerns. Besides, perl can use a shell that may not be
1138 fit for interactive use, and setting COMSPEC to such a shell may
1139 interfere with the proper functioning of other programs (which usually
1140 look in COMSPEC to find a shell fit for interactive use).
1142 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1143 X<PERL_ALLOW_NON_IFS_LSP>
1145 Set to 1 to allow the use of non-IFS compatible LSP's.
1146 Perl normally searches for an IFS-compatible LSP because this is required
1147 for its emulation of Windows sockets as real filehandles. However, this may
1148 cause problems if you have a firewall such as McAfee Guardian which requires
1149 all applications to use its LSP which is not IFS-compatible, because clearly
1150 Perl will normally avoid using such an LSP.
1151 Setting this environment variable to 1 means that Perl will simply use the
1152 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1153 happy (and in that particular case Perl still works too because McAfee
1154 Guardian's LSP actually plays some other games which allow applications
1155 requiring IFS compatibility to work).
1157 =item PERL_DEBUG_MSTATS
1158 X<PERL_DEBUG_MSTATS>
1160 Relevant only if perl is compiled with the malloc included with the perl
1161 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1162 If set, this causes memory statistics to be dumped after execution. If set
1163 to an integer greater than one, also causes memory statistics to be dumped
1166 =item PERL_DESTRUCT_LEVEL
1167 X<PERL_DESTRUCT_LEVEL>
1169 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1170 this controls the behavior of global destruction of objects and other
1171 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1173 =item PERL_DL_NONLAZY
1176 Set to one to have perl resolve B<all> undefined symbols when it loads
1177 a dynamic library. The default behaviour is to resolve symbols when
1178 they are used. Setting this variable is useful during testing of
1179 extensions as it ensures that you get an error on misspelled function
1180 names even if the test suite doesn't call it.
1185 If using the C<encoding> pragma without an explicit encoding name, the
1186 PERL_ENCODING environment variable is consulted for an encoding name.
1188 =item PERL_HASH_SEED
1191 (Since Perl 5.8.1.) Used to randomise perl's internal hash function.
1192 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1193 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1194 things, that hash keys will always have the same ordering between
1195 different runs of perl.
1197 Most hashes return elements in the same order as Perl 5.8.0 by default.
1198 On a hash by hash basis, if pathological data is detected during a hash
1199 key insertion, then that hash will switch to an alternative random hash
1202 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1203 If perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1204 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1206 If PERL_HASH_SEED is unset or set to a non-numeric string, perl uses
1207 the pseudorandom seed supplied by the operating system and libraries.
1209 B<Please note that the hash seed is sensitive information>. Hashes are
1210 randomized to protect against local and remote attacks against Perl
1211 code. By manually setting a seed this protection may be partially or
1214 See L<perlsec/"Algorithmic Complexity Attacks"> and
1215 L</PERL_HASH_SEED_DEBUG> for more information.
1217 =item PERL_HASH_SEED_DEBUG
1218 X<PERL_HASH_SEED_DEBUG>
1220 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1221 the hash seed at the beginning of execution. This, combined with
1222 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1223 behavior caused by hash randomization.
1225 B<Note that the hash seed is sensitive information>: by knowing it one
1226 can craft a denial-of-service attack against Perl code, even remotely,
1227 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1228 B<Do not disclose the hash seed> to people who don't need to know it.
1229 See also hash_seed() of L<Hash::Util>.
1231 =item PERL_ROOT (specific to the VMS port)
1234 A translation concealed rooted logical name that contains perl and the
1235 logical device for the @INC path on VMS only. Other logical names that
1236 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1237 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1238 L<perlvms> and in F<README.vms> in the Perl source distribution.
1243 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1244 signals behaviour (immediate but unsafe) is restored. If set to
1245 C<safe> the safe (or deferred) signals are used.
1246 See L<perlipc/"Deferred Signals (Safe Signals)">.
1251 Equivalent to the B<-C> command-line switch. Note that this is not
1252 a boolean variable-- setting this to C<"1"> is not the right way to
1253 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1254 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1255 your shell before starting Perl). See the description of the C<-C>
1256 switch for more information.
1258 =item SYS$LOGIN (specific to the VMS port)
1261 Used if chdir has no argument and HOME and LOGDIR are not set.
1265 Perl also has environment variables that control how Perl handles data
1266 specific to particular natural languages. See L<perllocale>.
1268 Apart from these, Perl uses no other environment variables, except
1269 to make them available to the program being executed, and to child
1270 processes. However, programs running setuid would do well to execute
1271 the following lines before doing anything else, just to keep people
1274 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1275 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1276 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};