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
408 262144 R Include reference counts of dumped variables (eg when using -Ds)
409 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
410 1048576 v Verbose: use in conjunction with other flags
411 2097152 C Copy On Write
412 4194304 A Consistency checks on internal structures
413 8388608 q quiet - currently only suppresses the "EXECUTING" message
415 All these flags require B<-DDEBUGGING> when you compile the Perl
416 executable (but see L<Devel::Peek>, L<re> which may change this).
417 See the F<INSTALL> file in the Perl source distribution
418 for how to do this. This flag is automatically set if you include B<-g>
419 option when C<Configure> asks you about optimizer/debugger flags.
421 If you're just trying to get a print out of each line of Perl code
422 as it executes, the way that C<sh -x> provides for shell scripts,
423 you can't use Perl's B<-D> switch. Instead do this
425 # If you have "env" utility
426 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
428 # Bourne shell syntax
429 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
432 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
434 See L<perldebug> for details and variations.
436 =item B<-e> I<commandline>
439 may be used to enter one line of program. If B<-e> is given, Perl
440 will not look for a filename in the argument list. Multiple B<-e>
441 commands may be given to build up a multi-line script. Make sure
442 to use semicolons where you would in a normal program.
444 =item B<-E> I<commandline>
447 behaves just like B<-e>, except that it implicitly enables all
448 optional features (in the main compilation unit). See L<feature>.
453 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
455 Perl can be built so that it by default will try to execute
456 F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block).
457 This is a hook that allows the sysadmin to customize how perl behaves.
458 It can for instance be used to add entries to the @INC array to make perl
459 find modules in non-standard locations.
461 =item B<-F>I<pattern>
464 specifies the pattern to split on if B<-a> is also in effect. The
465 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
466 put in single quotes. You can't use literal whitespace in the pattern.
471 prints a summary of the options.
473 =item B<-i>[I<extension>]
476 specifies that files processed by the C<E<lt>E<gt>> construct are to be
477 edited in-place. It does this by renaming the input file, opening the
478 output file by the original name, and selecting that output file as the
479 default for print() statements. The extension, if supplied, is used to
480 modify the name of the old file to make a backup copy, following these
483 If no extension is supplied, no backup is made and the current file is
486 If the extension doesn't contain a C<*>, then it is appended to the
487 end of the current filename as a suffix. If the extension does
488 contain one or more C<*> characters, then each C<*> is replaced
489 with the current filename. In Perl terms, you could think of this
492 ($backup = $extension) =~ s/\*/$file_name/g;
494 This allows you to add a prefix to the backup file, instead of (or in
495 addition to) a suffix:
497 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
499 Or even to place backup copies of the original files into another
500 directory (provided the directory already exists):
502 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
504 These sets of one-liners are equivalent:
506 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
507 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
509 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
510 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
512 From the shell, saying
514 $ perl -p -i.orig -e "s/foo/bar/; ... "
516 is the same as using the program:
518 #!/usr/bin/perl -pi.orig
521 which is equivalent to
524 $extension = '.orig';
526 if ($ARGV ne $oldargv) {
527 if ($extension !~ /\*/) {
528 $backup = $ARGV . $extension;
531 ($backup = $extension) =~ s/\*/$ARGV/g;
533 rename($ARGV, $backup);
534 open(ARGVOUT, ">$ARGV");
541 print; # this prints to original filename
545 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
546 know when the filename has changed. It does, however, use ARGVOUT for
547 the selected filehandle. Note that STDOUT is restored as the default
548 output filehandle after the loop.
550 As shown above, Perl creates the backup file whether or not any output
551 is actually changed. So this is just a fancy way to copy files:
553 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
555 $ perl -p -i'.orig' -e 1 file1 file2 file3...
557 You can use C<eof> without parentheses to locate the end of each input
558 file, in case you want to append to each file, or reset line numbering
559 (see example in L<perlfunc/eof>).
561 If, for a given file, Perl is unable to create the backup file as
562 specified in the extension then it will skip that file and continue on
563 with the next one (if it exists).
565 For a discussion of issues surrounding file permissions and B<-i>,
566 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?>.
568 You cannot use B<-i> to create directories or to strip extensions from
571 Perl does not expand C<~> in filenames, which is good, since some
572 folks use it for their backup files:
574 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
576 Note that because B<-i> renames or deletes the original file before
577 creating a new file of the same name, UNIX-style soft and hard links will
580 Finally, the B<-i> switch does not impede execution when no
581 files are given on the command line. In this case, no backup is made
582 (the original file cannot, of course, be determined) and processing
583 proceeds from STDIN to STDOUT as might be expected.
585 =item B<-I>I<directory>
588 Directories specified by B<-I> are prepended to the search path for
591 =item B<-l>[I<octnum>]
594 enables automatic line-ending processing. It has two separate
595 effects. First, it automatically chomps C<$/> (the input record
596 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
597 (the output record separator) to have the value of I<octnum> so
598 that any print statements will have that separator added back on.
599 If I<octnum> is omitted, sets C<$\> to the current value of
600 C<$/>. For instance, to trim lines to 80 columns:
602 perl -lpe 'substr($_, 80) = ""'
604 Note that the assignment C<$\ = $/> is done when the switch is processed,
605 so the input record separator can be different than the output record
606 separator if the B<-l> switch is followed by a B<-0> switch:
608 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
610 This sets C<$\> to newline and then sets C<$/> to the null character.
612 =item B<-m>[B<->]I<module>
615 =item B<-M>[B<->]I<module>
617 =item B<-M>[B<->]I<'module ...'>
619 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
621 B<-m>I<module> executes C<use> I<module> C<();> before executing your
624 B<-M>I<module> executes C<use> I<module> C<;> before executing your
625 program. You can use quotes to add extra code after the module name,
626 e.g., C<'-Mmodule qw(foo bar)'>.
628 If the first character after the B<-M> or B<-m> is a dash (C<->)
629 then the 'use' is replaced with 'no'.
631 A little builtin syntactic sugar means you can also say
632 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
633 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
634 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
635 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
636 removes the distinction between B<-m> and B<-M>.
638 A consequence of this is that B<-MFoo=number> never does a version check
639 (unless C<Foo::import()> itself is set up to do a version check, which
640 could happen for example if Foo inherits from Exporter.)
645 causes Perl to assume the following loop around your program, which
646 makes it iterate over filename arguments somewhat like B<sed -n> or
651 ... # your program goes here
654 Note that the lines are not printed by default. See B<-p> to have
655 lines printed. If a file named by an argument cannot be opened for
656 some reason, Perl warns you about it and moves on to the next file.
658 Here is an efficient way to delete all files that haven't been modified for
661 find . -mtime +7 -print | perl -nle unlink
663 This is faster than using the B<-exec> switch of B<find> because you don't
664 have to start a process on every filename found. It does suffer from
665 the bug of mishandling newlines in pathnames, which you can fix if
666 you follow the example under B<-0>.
668 C<BEGIN> and C<END> blocks may be used to capture control before or after
669 the implicit program loop, just as in B<awk>.
674 causes Perl to assume the following loop around your program, which
675 makes it iterate over filename arguments somewhat like B<sed>:
680 ... # your program goes here
682 print or die "-p destination: $!\n";
685 If a file named by an argument cannot be opened for some reason, Perl
686 warns you about it, and moves on to the next file. Note that the
687 lines are printed automatically. An error occurring during printing is
688 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
689 overrides a B<-n> switch.
691 C<BEGIN> and C<END> blocks may be used to capture control before or after
692 the implicit loop, just as in B<awk>.
697 enables rudimentary switch parsing for switches on the command
698 line after the program name but before any filename arguments (or before
699 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
700 corresponding variable in the Perl program. The following program
701 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
702 if it is invoked with B<-xyz=abc>.
705 if ($xyz) { print "$xyz\n" }
707 Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
708 with C<strict refs>. Also, when using this option on a script with
709 warnings enabled you may get a lot of spurious "used only once" warnings.
714 makes Perl use the PATH environment variable to search for the
715 program (unless the name of the program contains directory separators).
717 On some platforms, this also makes Perl append suffixes to the
718 filename while searching for it. For example, on Win32 platforms,
719 the ".bat" and ".cmd" suffixes are appended if a lookup for the
720 original name fails, and if the name does not already end in one
721 of those suffixes. If your Perl was compiled with DEBUGGING turned
722 on, using the -Dp switch to Perl shows how the search progresses.
724 Typically this is used to emulate #! startup on platforms that don't
725 support #!. Its also convenient when debugging a script that uses #!,
726 and is thus normally found by the shell's $PATH search mechanism.
728 This example works on many platforms that have a shell compatible with
732 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
733 if $running_under_some_shell;
735 The system ignores the first line and feeds the program to F</bin/sh>,
736 which proceeds to try to execute the Perl program as a shell script.
737 The shell executes the second line as a normal shell command, and thus
738 starts up the Perl interpreter. On some systems $0 doesn't always
739 contain the full pathname, so the B<-S> tells Perl to search for the
740 program if necessary. After Perl locates the program, it parses the
741 lines and ignores them because the variable $running_under_some_shell
742 is never true. If the program will be interpreted by csh, you will need
743 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
744 embedded spaces (and such) in the argument list. To start up sh rather
745 than csh, some systems may have to replace the #! line with a line
746 containing just a colon, which will be politely ignored by Perl. Other
747 systems can't control that, and need a totally devious construct that
748 will work under any of B<csh>, B<sh>, or Perl, such as the following:
750 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
751 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
752 if $running_under_some_shell;
754 If the filename supplied contains directory separators (i.e., is an
755 absolute or relative pathname), and if that file is not found,
756 platforms that append file extensions will do so and try to look
757 for the file with those extensions added, one by one.
759 On DOS-like platforms, if the program does not contain directory
760 separators, it will first be searched for in the current directory
761 before being searched for on the PATH. On Unix platforms, the
762 program will be searched for strictly on the PATH.
767 Like B<-T>, but taint checks will issue warnings rather than fatal
768 errors. These warnings can be controlled normally with C<no warnings
771 B<NOTE: this is not a substitute for -T.> This is meant only to be
772 used as a temporary development aid while securing legacy code:
773 for real production code and for new secure code written from scratch
774 always use the real B<-T>.
779 forces "taint" checks to be turned on so you can test them. Ordinarily
780 these checks are done only when running setuid or setgid. It's a
781 good idea to turn them on explicitly for programs that run on behalf
782 of someone else whom you might not necessarily trust, such as CGI
783 programs or any internet servers you might write in Perl. See
784 L<perlsec> for details. For security reasons, this option must be
785 seen by Perl quite early; usually this means it must appear early
786 on the command line or in the #! line for systems which support
792 This obsolete switch causes Perl to dump core after compiling your
793 program. You can then in theory take this core dump and turn it
794 into an executable file by using the B<undump> program (not supplied).
795 This speeds startup at the expense of some disk space (which you
796 can minimize by stripping the executable). (Still, a "hello world"
797 executable comes out to about 200K on my machine.) If you want to
798 execute a portion of your program before dumping, use the dump()
799 operator instead. Note: availability of B<undump> is platform
800 specific and may not be available for a specific port of Perl.
805 allows Perl to do unsafe operations. Currently the only "unsafe"
806 operations are attempting to unlink directories while running as
807 superuser, and running setuid programs with fatal taint checks turned
808 into warnings. Note that the B<-w> switch (or the C<$^W> variable)
809 must be used along with this option to actually I<generate> the
810 taint-check warnings.
815 prints the version and patchlevel of your perl executable.
820 prints summary of the major perl configuration values and the current
823 =item B<-V:>I<configvar>
825 Prints to STDOUT the value of the named configuration variable(s),
826 with multiples when your configvar argument looks like a regex (has
827 non-letters). For example:
830 libc='/lib/libc-2.2.4.so';
832 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
833 libc='/lib/libc-2.2.4.so';
835 libpth='/usr/local/lib /lib /usr/lib';
836 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
838 libc='/lib/libc-2.2.4.so';
842 Additionally, extra colons can be used to control formatting. A
843 trailing colon suppresses the linefeed and terminator ';', allowing
844 you to embed queries into shell commands. (mnemonic: PATH separator
847 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
848 compression-vars: zcat='' zip='zip' are here !
850 A leading colon removes the 'name=' part of the response, this allows
851 you to map to the name you need. (mnemonic: empty label)
853 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
856 Leading and trailing colons can be used together if you need
857 positional parameter values without the names. Note that in the case
858 below, the PERL_API params are returned in alphabetical order.
860 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
861 building_on 'linux' '5' '1' '9' now
866 prints warnings about dubious constructs, such as variable names
867 that are mentioned only once and scalar variables that are used
868 before being set, redefined subroutines, references to undefined
869 filehandles or filehandles opened read-only that you are attempting
870 to write on, values used as a number that don't look like numbers,
871 using an array as though it were a scalar, if your subroutines
872 recurse more than 100 deep, and innumerable other things.
874 This switch really just enables the internal C<$^W> variable. You
875 can disable or promote into fatal errors specific warnings using
876 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
877 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
878 facility is also available if you want to manipulate entire classes
879 of warnings; see L<warnings> or L<perllexwarn>.
884 Enables all warnings regardless of C<no warnings> or C<$^W>.
890 Disables all warnings regardless of C<use warnings> or C<$^W>.
896 =item B<-x>I<directory>
898 tells Perl that the program is embedded in a larger chunk of unrelated
899 ASCII text, such as in a mail message. Leading garbage will be
900 discarded until the first line that starts with #! and contains the
901 string "perl". Any meaningful switches on that line will be applied.
903 All references to line numbers by the program (warnings, errors, ...)
904 will treat the #! line as the first line.
905 Thus a warning on the 2nd line of the program (which is on the 100th
906 line in the file) will be reported as line 2, and not as line 100.
907 This can be overridden by using the #line directive.
908 (See L<perlsyn/"Plain-Old-Comments-(Not!)">)
910 If a directory name is specified, Perl will switch to that directory
911 before running the program. The B<-x> switch controls only the
912 disposal of leading garbage. The program must be terminated with
913 C<__END__> if there is trailing garbage to be ignored (the program
914 can process any or all of the trailing garbage via the DATA filehandle
917 The directory, if specified, must appear immediately following the B<-x>
918 with no intervening whitespace.
923 X<perl, environment variables>
930 Used if chdir has no argument.
935 Used if chdir has no argument and HOME is not set.
940 Used in executing subprocesses, and in finding the program if B<-S> is
946 A list of directories in which to look for Perl library
947 files before looking in the standard library and the current
948 directory. Any architecture-specific directories under the specified
949 locations are automatically included if they exist (this lookup
950 being done at interpreter startup time.)
952 If PERL5LIB is not defined, PERLLIB is used. Directories are separated
953 (like in PATH) by a colon on unixish platforms and by a semicolon on
954 Windows (the proper path separator being given by the command C<perl
957 When running taint checks (either because the program was running setuid
958 or setgid, or the B<-T> or B<-t> switch was specified), neither variable
959 is used. The program should instead say:
961 use lib "/my/directory";
966 Command-line options (switches). Switches in this variable are taken
967 as if they were on every Perl command line. Only the B<-[CDIMUdmtw]>
968 switches are allowed. When running taint checks (because the program
969 was running setuid or setgid, or the B<-T> switch was used), this
970 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
971 enabled, and any subsequent options ignored.
976 A space (or colon) separated list of PerlIO layers. If perl is built
977 to use PerlIO system for IO (the default) these layers effect perl's IO.
979 It is conventional to start layer names with a colon e.g. C<:perlio> to
980 emphasise their similarity to variable "attributes". But the code that parses
981 layer specification strings (which is also used to decode the PERLIO
982 environment variable) treats the colon as a separator.
984 An unset or empty PERLIO is equivalent to the default set of layers for
985 your platform, for example C<:unix:perlio> on UNIX-like systems
986 and C<:unix:crlf> on Windows and other DOS-like systems.
988 The list becomes the default for I<all> perl's IO. Consequently only built-in
989 layers can appear in this list, as external layers (such as :encoding()) need
990 IO in order to load them!. See L<"open pragma"|open> for how to add external
991 encodings as defaults.
993 The layers that it makes sense to include in the PERLIO environment
994 variable are briefly summarised below. For more details see L<PerlIO>.
1001 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
1002 Unlikely to be useful on its own in the global PERLIO environment variable.
1003 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1008 A layer which does CRLF to "\n" translation distinguishing "text" and
1009 "binary" files in the manner of MS-DOS and similar operating systems.
1010 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1011 as being an end-of-file marker.)
1016 A layer which implements "reading" of files by using C<mmap()> to
1017 make (whole) file appear in the process's address space, and then
1018 using that as PerlIO's "buffer".
1023 This is a re-implementation of "stdio-like" buffering written as a
1024 PerlIO "layer". As such it will call whatever layer is below it for
1025 its operations (typically C<:unix>).
1030 An experimental pseudolayer that removes the topmost layer.
1031 Use with the same care as is reserved for nitroglycerin.
1036 A pseudolayer that manipulates other layers. Applying the C<:raw>
1037 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1038 pass each byte as-is without any translation. In particular CRLF
1039 translation, and/or :utf8 intuited from locale are disabled.
1041 Unlike in the earlier versions of Perl C<:raw> is I<not>
1042 just the inverse of C<:crlf> - other layers which would affect the
1043 binary nature of the stream are also removed or disabled.
1048 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1049 library calls. The layer provides both buffering and IO.
1050 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1051 is platforms normal behaviour. You will need a C<:crlf> layer above it
1057 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1062 A pseudolayer that turns on a flag on the layer below to tell perl
1063 that output should be in utf8 and that input should be regarded as
1064 already in valid utf8 form. It does not check for validity and as such
1065 should be handled with caution for input. Generally C<:encoding(utf8)> is
1066 the best option when reading UTF-8 encoded data.
1071 On Win32 platforms this I<experimental> layer uses native "handle" IO
1072 rather than unix-like numeric file descriptor layer. Known to be
1073 buggy in this release.
1077 On all platforms the default set of layers should give acceptable results.
1079 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1080 Configure is setup to prefer "stdio" implementation if system's library
1081 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1084 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1085 has a number of bugs/mis-features for perl IO which are somewhat
1086 C compiler vendor/version dependent. Using our own C<crlf> layer as
1087 the buffer avoids those issues and makes things more uniform.
1088 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1091 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1092 compiler's numeric file descriptor routines. There is an experimental native
1093 C<win32> layer which is expected to be enhanced and should eventually be
1094 the default under Win32.
1099 If set to the name of a file or device then certain operations of PerlIO
1100 sub-system will be logged to that file (opened as append). Typical uses
1103 PERLIO_DEBUG=/dev/tty perl script ...
1105 and Win32 approximate equivalent:
1107 set PERLIO_DEBUG=CON
1110 This functionality is disabled for setuid scripts and for scripts run
1116 A list of directories in which to look for Perl library
1117 files before looking in the standard library and the current directory.
1118 If PERL5LIB is defined, PERLLIB is not used.
1123 The command used to load the debugger code. The default is:
1125 BEGIN { require 'perl5db.pl' }
1127 =item PERL5DB_THREADED
1130 If set to a true value, indicates to the debugger that the code being
1131 debugged uses threads.
1133 =item PERL5SHELL (specific to the Win32 port)
1136 May be set to an alternative shell that perl must use internally for
1137 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1138 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1139 to be space-separated. Precede any character that needs to be protected
1140 (like a space or backslash) with a backslash.
1142 Note that Perl doesn't use COMSPEC for this purpose because
1143 COMSPEC has a high degree of variability among users, leading to
1144 portability concerns. Besides, perl can use a shell that may not be
1145 fit for interactive use, and setting COMSPEC to such a shell may
1146 interfere with the proper functioning of other programs (which usually
1147 look in COMSPEC to find a shell fit for interactive use).
1149 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1150 X<PERL_ALLOW_NON_IFS_LSP>
1152 Set to 1 to allow the use of non-IFS compatible LSP's.
1153 Perl normally searches for an IFS-compatible LSP because this is required
1154 for its emulation of Windows sockets as real filehandles. However, this may
1155 cause problems if you have a firewall such as McAfee Guardian which requires
1156 all applications to use its LSP which is not IFS-compatible, because clearly
1157 Perl will normally avoid using such an LSP.
1158 Setting this environment variable to 1 means that Perl will simply use the
1159 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1160 happy (and in that particular case Perl still works too because McAfee
1161 Guardian's LSP actually plays some other games which allow applications
1162 requiring IFS compatibility to work).
1164 =item PERL_DEBUG_MSTATS
1165 X<PERL_DEBUG_MSTATS>
1167 Relevant only if perl is compiled with the malloc included with the perl
1168 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1169 If set, this causes memory statistics to be dumped after execution. If set
1170 to an integer greater than one, also causes memory statistics to be dumped
1173 =item PERL_DESTRUCT_LEVEL
1174 X<PERL_DESTRUCT_LEVEL>
1176 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1177 this controls the behavior of global destruction of objects and other
1178 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1180 =item PERL_DL_NONLAZY
1183 Set to one to have perl resolve B<all> undefined symbols when it loads
1184 a dynamic library. The default behaviour is to resolve symbols when
1185 they are used. Setting this variable is useful during testing of
1186 extensions as it ensures that you get an error on misspelled function
1187 names even if the test suite doesn't call it.
1192 If using the C<encoding> pragma without an explicit encoding name, the
1193 PERL_ENCODING environment variable is consulted for an encoding name.
1195 =item PERL_HASH_SEED
1198 (Since Perl 5.8.1.) Used to randomise perl's internal hash function.
1199 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1200 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1201 things, that hash keys will always have the same ordering between
1202 different runs of perl.
1204 Most hashes return elements in the same order as Perl 5.8.0 by default.
1205 On a hash by hash basis, if pathological data is detected during a hash
1206 key insertion, then that hash will switch to an alternative random hash
1209 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1210 If perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1211 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1213 If PERL_HASH_SEED is unset or set to a non-numeric string, perl uses
1214 the pseudorandom seed supplied by the operating system and libraries.
1216 B<Please note that the hash seed is sensitive information>. Hashes are
1217 randomized to protect against local and remote attacks against Perl
1218 code. By manually setting a seed this protection may be partially or
1221 See L<perlsec/"Algorithmic Complexity Attacks"> and
1222 L</PERL_HASH_SEED_DEBUG> for more information.
1224 =item PERL_HASH_SEED_DEBUG
1225 X<PERL_HASH_SEED_DEBUG>
1227 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1228 the hash seed at the beginning of execution. This, combined with
1229 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1230 behavior caused by hash randomization.
1232 B<Note that the hash seed is sensitive information>: by knowing it one
1233 can craft a denial-of-service attack against Perl code, even remotely,
1234 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1235 B<Do not disclose the hash seed> to people who don't need to know it.
1236 See also hash_seed() of L<Hash::Util>.
1238 =item PERL_ROOT (specific to the VMS port)
1241 A translation concealed rooted logical name that contains perl and the
1242 logical device for the @INC path on VMS only. Other logical names that
1243 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1244 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1245 L<perlvms> and in F<README.vms> in the Perl source distribution.
1250 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1251 signals behaviour (immediate but unsafe) is restored. If set to
1252 C<safe> the safe (or deferred) signals are used.
1253 See L<perlipc/"Deferred Signals (Safe Signals)">.
1258 Equivalent to the B<-C> command-line switch. Note that this is not
1259 a boolean variable-- setting this to C<"1"> is not the right way to
1260 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1261 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1262 your shell before starting Perl). See the description of the C<-C>
1263 switch for more information.
1265 =item SYS$LOGIN (specific to the VMS port)
1268 Used if chdir has no argument and HOME and LOGDIR are not set.
1272 Perl also has environment variables that control how Perl handles data
1273 specific to particular natural languages. See L<perllocale>.
1275 Apart from these, Perl uses no other environment variables, except
1276 to make them available to the program being executed, and to child
1277 processes. However, programs running setuid would do well to execute
1278 the following lines before doing anything else, just to keep people
1281 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1282 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1283 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};