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<-A>[I<module>][=I<assertions>] ]>
13 S<[ B<-C [I<number/list>] >]>
17 S<[ B<-i>[I<extension>] ]>
18 S<[ B<-eE> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
22 The normal way to run a Perl program is by making it directly
23 executable, or else by passing the name of the source file as an
24 argument on the command line. (An interactive Perl environment
25 is also possible--see L<perldebug> for details on how to do that.)
26 Upon startup, Perl looks for your program in one of the following
33 Specified line by line via B<-e> or B<-E> switches on the command line.
37 Contained in the file specified by the first filename on the command line.
38 (Note that systems supporting the #! notation invoke interpreters this
39 way. See L<Location of Perl>.)
43 Passed in implicitly via standard input. This works only if there are
44 no filename arguments--to pass arguments to a STDIN-read program you
45 must explicitly specify a "-" for the program name.
49 With methods 2 and 3, Perl starts parsing the input file from the
50 beginning, unless you've specified a B<-x> switch, in which case it
51 scans for the first line starting with #! and containing the word
52 "perl", and starts there instead. This is useful for running a program
53 embedded in a larger message. (In this case you would indicate the end
54 of the program using the C<__END__> token.)
56 The #! line is always examined for switches as the line is being
57 parsed. Thus, if you're on a machine that allows only one argument
58 with the #! line, or worse, doesn't even recognize the #! line, you
59 still can get consistent switch behavior regardless of how Perl was
60 invoked, even if B<-x> was used to find the beginning of the program.
62 Because historically some operating systems silently chopped off
63 kernel interpretation of the #! line after 32 characters, some
64 switches may be passed in on the command line, and some may not;
65 you could even get a "-" without its letter, if you're not careful.
66 You probably want to make sure that all your switches fall either
67 before or after that 32-character boundary. Most switches don't
68 actually care if they're processed redundantly, but getting a "-"
69 instead of a complete switch could cause Perl to try to execute
70 standard input instead of your program. And a partial B<-I> switch
71 could also cause odd results.
73 Some switches do care if they are processed twice, for instance
74 combinations of B<-l> and B<-0>. Either put all the switches after
75 the 32-character boundary (if applicable), or replace the use of
76 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
78 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
79 The sequences "-*" and "- " are specifically ignored so that you could,
80 if you were so inclined, say
82 #!/bin/sh -- # -*- perl -*- -p
83 eval 'exec perl -wS $0 ${1+"$@"}'
84 if $running_under_some_shell;
86 to let Perl see the B<-p> switch.
88 A similar trick involves the B<env> program, if you have it.
92 The examples above use a relative path to the perl interpreter,
93 getting whatever version is first in the user's path. If you want
94 a specific version of Perl, say, perl5.005_57, you should place
95 that directly in the #! line's path.
97 If the #! line does not contain the word "perl", the program named after
98 the #! is executed instead of the Perl interpreter. This is slightly
99 bizarre, but it helps people on machines that don't do #!, because they
100 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
101 dispatch the program to the correct interpreter for them.
103 After locating your program, Perl compiles the entire program to an
104 internal form. If there are any compilation errors, execution of the
105 program is not attempted. (This is unlike the typical shell script,
106 which might run part-way through before finding a syntax error.)
108 If the program is syntactically correct, it is executed. If the program
109 runs off the end without hitting an exit() or die() operator, an implicit
110 C<exit(0)> is provided to indicate successful completion.
112 =head2 #! and quoting on non-Unix systems
115 Unix's #! technique can be simulated on other systems:
123 extproc perl -S -your_switches
125 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
130 Create a batch file to run your program, and codify it in
131 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
132 distribution for more information).
136 The Win95/NT installation, when using the ActiveState installer for Perl,
137 will modify the Registry to associate the F<.pl> extension with the perl
138 interpreter. If you install Perl by other means (including building from
139 the sources), you may have to modify the Registry yourself. Note that
140 this means you can no longer tell the difference between an executable
141 Perl program and a Perl library file.
145 Under "Classic" MacOS, a perl program will have the appropriate Creator and
146 Type, so that double-clicking them will invoke the MacPerl application.
147 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
148 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
154 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
155 $ exit++ + ++$status != 0 and $exit = $status = undef;
157 at the top of your program, where B<-mysw> are any command line switches you
158 want to pass to Perl. You can now invoke the program directly, by saying
159 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
160 via F<DCL$PATH> by just using the name of the program).
162 This incantation is a bit much to remember, but Perl will display it for
163 you if you say C<perl "-V:startperl">.
167 Command-interpreters on non-Unix systems have rather different ideas
168 on quoting than Unix shells. You'll need to learn the special
169 characters in your command-interpreter (C<*>, C<\> and C<"> are
170 common) and how to protect whitespace and these characters to run
171 one-liners (see B<-e> below).
173 On some systems, you may have to change single-quotes to double ones,
174 which you must I<not> do on Unix or Plan 9 systems. You might also
175 have to change a single % to a %%.
180 perl -e 'print "Hello world\n"'
183 perl -e "print \"Hello world\n\""
186 print "Hello world\n"
187 (then Run "Myscript" or Shift-Command-R)
190 perl -e "print ""Hello world\n"""
192 The problem is that none of this is reliable: it depends on the
193 command and it is entirely possible neither works. If B<4DOS> were
194 the command shell, this would probably work better:
196 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
198 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
199 when nobody was looking, but just try to find documentation for its
202 Under the Macintosh, it depends which environment you are using. The MacPerl
203 shell, or MPW, is much like Unix shells in its support for several
204 quoting variants, except that it makes free use of the Macintosh's non-ASCII
205 characters as control characters.
207 There is no general solution to all of this. It's just a mess.
209 =head2 Location of Perl
210 X<perl, location of interpreter>
212 It may seem obvious to say, but Perl is useful only when users can
213 easily find it. When possible, it's good for both F</usr/bin/perl>
214 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
215 that can't be done, system administrators are strongly encouraged
216 to put (symlinks to) perl and its accompanying utilities into a
217 directory typically found along a user's PATH, or in some other
218 obvious and convenient place.
220 In this documentation, C<#!/usr/bin/perl> on the first line of the program
221 will stand in for whatever method works on your system. You are
222 advised to use a specific path if you care about a specific version.
224 #!/usr/local/bin/perl5.00554
226 or if you just want to be running at least version, place a statement
227 like this at the top of your program:
231 =head2 Command Switches
232 X<perl, command switches> X<command switches>
234 As with all standard commands, a single-character switch may be
235 clustered with the following switch, if any.
237 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
243 =item B<-0>[I<octal/hexadecimal>]
246 specifies the input record separator (C<$/>) as an octal or
247 hexadecimal number. If there are no digits, the null character is the
248 separator. Other switches may precede or follow the digits. For
249 example, if you have a version of B<find> which can print filenames
250 terminated by the null character, you can say this:
252 find . -name '*.orig' -print0 | perl -n0e unlink
254 The special value 00 will cause Perl to slurp files in paragraph mode.
255 The value 0777 will cause Perl to slurp files whole because there is no
256 legal byte with that value.
258 If you want to specify any Unicode character, use the hexadecimal
259 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
260 (This means that you cannot use the C<-x> with a directory name that
261 consists of hexadecimal digits.)
263 =item B<-A[I<module>][=I<assertions>]>
266 Activates the assertions given after the equal sign as a comma-separated
267 list of assertion names or regular expressions. If no assertion name
268 is given, activates all assertions.
270 The module L<assertions::activate> is used by default to activate the
271 selected assertions. An alternate module may be specified including
272 its name between the switch and the equal sign.
274 See L<assertions> and L<assertions::activate>.
279 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
280 split command to the @F array is done as the first thing inside the
281 implicit while loop produced by the B<-n> or B<-p>.
283 perl -ane 'print pop(@F), "\n";'
292 An alternate delimiter may be specified using B<-F>.
294 =item B<-C [I<number/list>]>
297 The C<-C> flag controls some Unicode of the Perl Unicode features.
299 As of 5.8.1, the C<-C> can be followed either by a number or a list
300 of option letters. The letters, their numeric values, and effects
301 are as follows; listing the letters is equal to summing the numbers.
303 I 1 STDIN is assumed to be in UTF-8
304 O 2 STDOUT will be in UTF-8
305 E 4 STDERR will be in UTF-8
307 i 8 UTF-8 is the default PerlIO layer for input streams
308 o 16 UTF-8 is the default PerlIO layer for output streams
310 A 32 the @ARGV elements are expected to be strings encoded
312 L 64 normally the "IOEioA" are unconditional,
313 the L makes them conditional on the locale environment
314 variables (the LC_ALL, LC_TYPE, and LANG, in the order
315 of decreasing precedence) -- if the variables indicate
316 UTF-8, then the selected "IOEioA" are in effect
317 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching code in
320 =for documenting_the_underdocumented
321 perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
324 perltodo mentions Unicode in %ENV and filenames. I guess that these will be
325 options e and f (or F).
327 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
328 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
331 The C<io> options mean that any subsequent open() (or similar I/O
332 operations) will have the C<:utf8> PerlIO layer implicitly applied
333 to them, in other words, UTF-8 is expected from any input stream,
334 and UTF-8 is produced to any output stream. This is just the default,
335 with explicit layers in open() and with binmode() one can manipulate
338 C<-C> on its own (not followed by any number or option list), or the
339 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
340 same effect as C<-CSDL>. In other words, the standard I/O handles and
341 the default C<open()> layer are UTF-8-fied B<but> only if the locale
342 environment variables indicate a UTF-8 locale. This behaviour follows
343 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
345 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
346 disable all the above Unicode features.
348 The read-only magic variable C<${^UNICODE}> reflects the numeric value
349 of this setting. This is variable is set during Perl startup and is
350 thereafter read-only. If you want runtime effects, use the three-arg
351 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
352 and the C<open> pragma (see L<open>).
354 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
355 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
356 This feature was practically unused, however, and the command line
357 switch was therefore "recycled".)
362 causes Perl to check the syntax of the program and then exit without
363 executing it. Actually, it I<will> execute C<BEGIN>, C<UNITCHECK>,
364 C<CHECK>, and C<use> blocks, because these are considered as occurring
365 outside the execution of your program. C<INIT> and C<END> blocks,
366 however, will be skipped.
373 runs the program under the Perl debugger. See L<perldebug>.
374 If B<t> is specified, it indicates to the debugger that threads
375 will be used in the code being debugged.
377 =item B<-d:>I<foo[=bar,baz]>
380 =item B<-dt:>I<foo[=bar,baz]>
382 runs the program under the control of a debugging, profiling, or
383 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
384 the program using the Devel::DProf profiler. As with the B<-M>
385 flag, options may be passed to the Devel::foo package where they
386 will be received and interpreted by the Devel::foo::import routine.
387 The comma-separated list of options must follow a C<=> character.
388 If B<t> is specified, it indicates to the debugger that threads
389 will be used in the code being debugged.
392 =item B<-D>I<letters>
393 X<-D> X<DEBUGGING> X<-DDEBUGGING>
397 sets debugging flags. To watch how it executes your program, use
398 B<-Dtls>. (This works only if debugging is compiled into your
399 Perl.) Another nice value is B<-Dx>, which lists your compiled
400 syntax tree. And B<-Dr> displays compiled regular expressions;
401 the format of the output is explained in L<perldebguts>.
403 As an alternative, specify a number instead of list of letters (e.g.,
404 B<-D14> is equivalent to B<-Dtls>):
406 1 p Tokenizing and parsing (with v, displays parse stack)
407 2 s Stack snapshots (with v, displays all stacks)
408 4 l Context (loop) stack processing
410 16 o Method and overloading resolution
411 32 c String/numeric conversions
412 64 P Print profiling info, preprocessor command for -P, source file input state
413 128 m Memory allocation
414 256 f Format processing
415 512 r Regular expression parsing and execution
416 1024 x Syntax tree dump
417 2048 u Tainting checks
418 4096 (Obsolete, previously used for LEAKTEST)
419 8192 H Hash dump -- usurps values()
420 16384 X Scratchpad allocation
422 65536 S Thread synchronization
424 262144 R Include reference counts of dumped variables (eg when using -Ds)
425 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
426 1048576 v Verbose: use in conjunction with other flags
427 2097152 C Copy On Write
428 4194304 A Consistency checks on internal structures
429 8388608 q quiet - currently only suppresses the "EXECUTING" message
431 All these flags require B<-DDEBUGGING> when you compile the Perl
432 executable (but see L<Devel::Peek>, L<re> which may change this).
433 See the F<INSTALL> file in the Perl source distribution
434 for how to do this. This flag is automatically set if you include B<-g>
435 option when C<Configure> asks you about optimizer/debugger flags.
437 If you're just trying to get a print out of each line of Perl code
438 as it executes, the way that C<sh -x> provides for shell scripts,
439 you can't use Perl's B<-D> switch. Instead do this
441 # If you have "env" utility
442 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
444 # Bourne shell syntax
445 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
448 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
450 See L<perldebug> for details and variations.
452 =item B<-e> I<commandline>
455 may be used to enter one line of program. If B<-e> is given, Perl
456 will not look for a filename in the argument list. Multiple B<-e>
457 commands may be given to build up a multi-line script. Make sure
458 to use semicolons where you would in a normal program.
460 =item B<-E> I<commandline>
463 behaves just like B<-e>, except that it implicitly enables all
464 optional features (in the main compilation unit). See L<feature>.
469 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
471 Perl can be built so that it by default will try to execute
472 F<$Config{sitelib}/sitecustomize.pl> at startup. This is a hook that
473 allows the sysadmin to customize how perl behaves. It can for
474 instance be used to add entries to the @INC array to make perl find
475 modules in non-standard locations.
477 =item B<-F>I<pattern>
480 specifies the pattern to split on if B<-a> is also in effect. The
481 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
482 put in single quotes. You can't use literal whitespace in the pattern.
487 prints a summary of the options.
489 =item B<-i>[I<extension>]
492 specifies that files processed by the C<E<lt>E<gt>> construct are to be
493 edited in-place. It does this by renaming the input file, opening the
494 output file by the original name, and selecting that output file as the
495 default for print() statements. The extension, if supplied, is used to
496 modify the name of the old file to make a backup copy, following these
499 If no extension is supplied, no backup is made and the current file is
502 If the extension doesn't contain a C<*>, then it is appended to the
503 end of the current filename as a suffix. If the extension does
504 contain one or more C<*> characters, then each C<*> is replaced
505 with the current filename. In Perl terms, you could think of this
508 ($backup = $extension) =~ s/\*/$file_name/g;
510 This allows you to add a prefix to the backup file, instead of (or in
511 addition to) a suffix:
513 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
515 Or even to place backup copies of the original files into another
516 directory (provided the directory already exists):
518 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
520 These sets of one-liners are equivalent:
522 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
523 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
525 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
526 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
528 From the shell, saying
530 $ perl -p -i.orig -e "s/foo/bar/; ... "
532 is the same as using the program:
534 #!/usr/bin/perl -pi.orig
537 which is equivalent to
540 $extension = '.orig';
542 if ($ARGV ne $oldargv) {
543 if ($extension !~ /\*/) {
544 $backup = $ARGV . $extension;
547 ($backup = $extension) =~ s/\*/$ARGV/g;
549 rename($ARGV, $backup);
550 open(ARGVOUT, ">$ARGV");
557 print; # this prints to original filename
561 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
562 know when the filename has changed. It does, however, use ARGVOUT for
563 the selected filehandle. Note that STDOUT is restored as the default
564 output filehandle after the loop.
566 As shown above, Perl creates the backup file whether or not any output
567 is actually changed. So this is just a fancy way to copy files:
569 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
571 $ perl -p -i'.orig' -e 1 file1 file2 file3...
573 You can use C<eof> without parentheses to locate the end of each input
574 file, in case you want to append to each file, or reset line numbering
575 (see example in L<perlfunc/eof>).
577 If, for a given file, Perl is unable to create the backup file as
578 specified in the extension then it will skip that file and continue on
579 with the next one (if it exists).
581 For a discussion of issues surrounding file permissions and B<-i>,
582 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?>.
584 You cannot use B<-i> to create directories or to strip extensions from
587 Perl does not expand C<~> in filenames, which is good, since some
588 folks use it for their backup files:
590 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
592 Note that because B<-i> renames or deletes the original file before
593 creating a new file of the same name, UNIX-style soft and hard links will
596 Finally, the B<-i> switch does not impede execution when no
597 files are given on the command line. In this case, no backup is made
598 (the original file cannot, of course, be determined) and processing
599 proceeds from STDIN to STDOUT as might be expected.
601 =item B<-I>I<directory>
604 Directories specified by B<-I> are prepended to the search path for
605 modules (C<@INC>), and also tells the C preprocessor where to search for
606 include files. The C preprocessor is invoked with B<-P>; by default it
607 searches /usr/include and /usr/lib/perl.
609 =item B<-l>[I<octnum>]
612 enables automatic line-ending processing. It has two separate
613 effects. First, it automatically chomps C<$/> (the input record
614 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
615 (the output record separator) to have the value of I<octnum> so
616 that any print statements will have that separator added back on.
617 If I<octnum> is omitted, sets C<$\> to the current value of
618 C<$/>. For instance, to trim lines to 80 columns:
620 perl -lpe 'substr($_, 80) = ""'
622 Note that the assignment C<$\ = $/> is done when the switch is processed,
623 so the input record separator can be different than the output record
624 separator if the B<-l> switch is followed by a B<-0> switch:
626 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
628 This sets C<$\> to newline and then sets C<$/> to the null character.
630 =item B<-m>[B<->]I<module>
633 =item B<-M>[B<->]I<module>
635 =item B<-M>[B<->]I<'module ...'>
637 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
639 B<-m>I<module> executes C<use> I<module> C<();> before executing your
642 B<-M>I<module> executes C<use> I<module> C<;> before executing your
643 program. You can use quotes to add extra code after the module name,
644 e.g., C<'-Mmodule qw(foo bar)'>.
646 If the first character after the B<-M> or B<-m> is a dash (C<->)
647 then the 'use' is replaced with 'no'.
649 A little builtin syntactic sugar means you can also say
650 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
651 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
652 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
653 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
654 removes the distinction between B<-m> and B<-M>.
656 A consequence of this is that B<-MFoo=number> never does a version check
657 (unless C<Foo::import()> itself is set up to do a version check, which
658 could happen for example if Foo inherits from Exporter.)
663 causes Perl to assume the following loop around your program, which
664 makes it iterate over filename arguments somewhat like B<sed -n> or
669 ... # your program goes here
672 Note that the lines are not printed by default. See B<-p> to have
673 lines printed. If a file named by an argument cannot be opened for
674 some reason, Perl warns you about it and moves on to the next file.
676 Here is an efficient way to delete all files that haven't been modified for
679 find . -mtime +7 -print | perl -nle unlink
681 This is faster than using the B<-exec> switch of B<find> because you don't
682 have to start a process on every filename found. It does suffer from
683 the bug of mishandling newlines in pathnames, which you can fix if
684 you follow the example under B<-0>.
686 C<BEGIN> and C<END> blocks may be used to capture control before or after
687 the implicit program loop, just as in B<awk>.
692 causes Perl to assume the following loop around your program, which
693 makes it iterate over filename arguments somewhat like B<sed>:
698 ... # your program goes here
700 print or die "-p destination: $!\n";
703 If a file named by an argument cannot be opened for some reason, Perl
704 warns you about it, and moves on to the next file. Note that the
705 lines are printed automatically. An error occurring during printing is
706 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
707 overrides a B<-n> switch.
709 C<BEGIN> and C<END> blocks may be used to capture control before or after
710 the implicit loop, just as in B<awk>.
715 B<NOTE: Use of -P is strongly discouraged because of its inherent
716 problems, including poor portability.>
718 This option causes your program to be run through the C preprocessor before
719 compilation by Perl. Because both comments and B<cpp> directives begin
720 with the # character, you should avoid starting comments with any words
721 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
723 If you're considering using C<-P>, you might also want to look at the
724 Filter::cpp module from CPAN.
726 The problems of -P include, but are not limited to:
732 The C<#!> line is stripped, so any switches there don't apply.
736 A C<-P> on a C<#!> line doesn't work.
740 B<All> lines that begin with (whitespace and) a C<#> but
741 do not look like cpp commands, are stripped, including anything
742 inside Perl strings, regular expressions, and here-docs .
746 In some platforms the C preprocessor knows too much: it knows about
747 the C++ -style until-end-of-line comments starting with C<"//">.
748 This will cause problems with common Perl constructs like
752 because after -P this will became illegal code
756 The workaround is to use some other quoting separator than C<"/">,
757 like for example C<"!">:
765 It requires not only a working C preprocessor but also a working
766 F<sed>. If not on UNIX, you are probably out of luck on this.
770 Script line numbers are not preserved.
774 The C<-x> does not work with C<-P>.
781 enables rudimentary switch parsing for switches on the command
782 line after the program name but before any filename arguments (or before
783 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
784 corresponding variable in the Perl program. The following program
785 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
786 if it is invoked with B<-xyz=abc>.
789 if ($xyz) { print "$xyz\n" }
791 Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
792 with C<strict refs>. Also, when using this option on a script with
793 warnings enabled you may get a lot of spurious "used only once" warnings.
798 makes Perl use the PATH environment variable to search for the
799 program (unless the name of the program contains directory separators).
801 On some platforms, this also makes Perl append suffixes to the
802 filename while searching for it. For example, on Win32 platforms,
803 the ".bat" and ".cmd" suffixes are appended if a lookup for the
804 original name fails, and if the name does not already end in one
805 of those suffixes. If your Perl was compiled with DEBUGGING turned
806 on, using the -Dp switch to Perl shows how the search progresses.
808 Typically this is used to emulate #! startup on platforms that don't
809 support #!. Its also convenient when debugging a script that uses #!,
810 and is thus normally found by the shell's $PATH search mechanism.
812 This example works on many platforms that have a shell compatible with
816 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
817 if $running_under_some_shell;
819 The system ignores the first line and feeds the program to F</bin/sh>,
820 which proceeds to try to execute the Perl program as a shell script.
821 The shell executes the second line as a normal shell command, and thus
822 starts up the Perl interpreter. On some systems $0 doesn't always
823 contain the full pathname, so the B<-S> tells Perl to search for the
824 program if necessary. After Perl locates the program, it parses the
825 lines and ignores them because the variable $running_under_some_shell
826 is never true. If the program will be interpreted by csh, you will need
827 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
828 embedded spaces (and such) in the argument list. To start up sh rather
829 than csh, some systems may have to replace the #! line with a line
830 containing just a colon, which will be politely ignored by Perl. Other
831 systems can't control that, and need a totally devious construct that
832 will work under any of B<csh>, B<sh>, or Perl, such as the following:
834 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
835 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
836 if $running_under_some_shell;
838 If the filename supplied contains directory separators (i.e., is an
839 absolute or relative pathname), and if that file is not found,
840 platforms that append file extensions will do so and try to look
841 for the file with those extensions added, one by one.
843 On DOS-like platforms, if the program does not contain directory
844 separators, it will first be searched for in the current directory
845 before being searched for on the PATH. On Unix platforms, the
846 program will be searched for strictly on the PATH.
851 Like B<-T>, but taint checks will issue warnings rather than fatal
852 errors. These warnings can be controlled normally with C<no warnings
855 B<NOTE: this is not a substitute for -T.> This is meant only to be
856 used as a temporary development aid while securing legacy code:
857 for real production code and for new secure code written from scratch
858 always use the real B<-T>.
863 forces "taint" checks to be turned on so you can test them. Ordinarily
864 these checks are done only when running setuid or setgid. It's a
865 good idea to turn them on explicitly for programs that run on behalf
866 of someone else whom you might not necessarily trust, such as CGI
867 programs or any internet servers you might write in Perl. See
868 L<perlsec> for details. For security reasons, this option must be
869 seen by Perl quite early; usually this means it must appear early
870 on the command line or in the #! line for systems which support
876 This obsolete switch causes Perl to dump core after compiling your
877 program. You can then in theory take this core dump and turn it
878 into an executable file by using the B<undump> program (not supplied).
879 This speeds startup at the expense of some disk space (which you
880 can minimize by stripping the executable). (Still, a "hello world"
881 executable comes out to about 200K on my machine.) If you want to
882 execute a portion of your program before dumping, use the dump()
883 operator instead. Note: availability of B<undump> is platform
884 specific and may not be available for a specific port of Perl.
886 This switch has been superseded in favor of the new Perl code
887 generator backends to the compiler. See L<B> and L<B::Bytecode>
893 allows Perl to do unsafe operations. Currently the only "unsafe"
894 operations are attempting to unlink directories while running as
895 superuser, and running setuid programs with fatal taint checks turned
896 into warnings. Note that the B<-w> switch (or the C<$^W> variable)
897 must be used along with this option to actually I<generate> the
898 taint-check warnings.
903 prints the version and patchlevel of your perl executable.
908 prints summary of the major perl configuration values and the current
911 =item B<-V:>I<configvar>
913 Prints to STDOUT the value of the named configuration variable(s),
914 with multiples when your configvar argument looks like a regex (has
915 non-letters). For example:
918 libc='/lib/libc-2.2.4.so';
920 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
921 libc='/lib/libc-2.2.4.so';
923 libpth='/usr/local/lib /lib /usr/lib';
924 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
926 libc='/lib/libc-2.2.4.so';
930 Additionally, extra colons can be used to control formatting. A
931 trailing colon suppresses the linefeed and terminator ';', allowing
932 you to embed queries into shell commands. (mnemonic: PATH separator
935 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
936 compression-vars: zcat='' zip='zip' are here !
938 A leading colon removes the 'name=' part of the response, this allows
939 you to map to the name you need. (mnemonic: empty label)
941 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
944 Leading and trailing colons can be used together if you need
945 positional parameter values without the names. Note that in the case
946 below, the PERL_API params are returned in alphabetical order.
948 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
949 building_on 'linux' '5' '1' '9' now
954 prints warnings about dubious constructs, such as variable names
955 that are mentioned only once and scalar variables that are used
956 before being set, redefined subroutines, references to undefined
957 filehandles or filehandles opened read-only that you are attempting
958 to write on, values used as a number that don't look like numbers,
959 using an array as though it were a scalar, if your subroutines
960 recurse more than 100 deep, and innumerable other things.
962 This switch really just enables the internal C<$^W> variable. You
963 can disable or promote into fatal errors specific warnings using
964 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
965 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
966 facility is also available if you want to manipulate entire classes
967 of warnings; see L<warnings> or L<perllexwarn>.
972 Enables all warnings regardless of C<no warnings> or C<$^W>.
978 Disables all warnings regardless of C<use warnings> or C<$^W>.
984 =item B<-x> I<directory>
986 tells Perl that the program is embedded in a larger chunk of unrelated
987 ASCII text, such as in a mail message. Leading garbage will be
988 discarded until the first line that starts with #! and contains the
989 string "perl". Any meaningful switches on that line will be applied.
990 If a directory name is specified, Perl will switch to that directory
991 before running the program. The B<-x> switch controls only the
992 disposal of leading garbage. The program must be terminated with
993 C<__END__> if there is trailing garbage to be ignored (the program
994 can process any or all of the trailing garbage via the DATA filehandle
1000 X<perl, environment variables>
1007 Used if chdir has no argument.
1012 Used if chdir has no argument and HOME is not set.
1017 Used in executing subprocesses, and in finding the program if B<-S> is
1023 A list of directories in which to look for Perl library
1024 files before looking in the standard library and the current
1025 directory. Any architecture-specific directories under the specified
1026 locations are automatically included if they exist. If PERL5LIB is not
1027 defined, PERLLIB is used. Directories are separated (like in PATH) by
1028 a colon on unixish platforms and by a semicolon on Windows (the proper
1029 path separator being given by the command C<perl -V:path_sep>).
1031 When running taint checks (either because the program was running setuid
1032 or setgid, or the B<-T> switch was used), neither variable is used.
1033 The program should instead say:
1035 use lib "/my/directory";
1040 Command-line options (switches). Switches in this variable are taken
1041 as if they were on every Perl command line. Only the B<-[CDIMUdmtwA]>
1042 switches are allowed. When running taint checks (because the program
1043 was running setuid or setgid, or the B<-T> switch was used), this
1044 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
1045 enabled, and any subsequent options ignored.
1050 A space (or colon) separated list of PerlIO layers. If perl is built
1051 to use PerlIO system for IO (the default) these layers effect perl's IO.
1053 It is conventional to start layer names with a colon e.g. C<:perlio> to
1054 emphasise their similarity to variable "attributes". But the code that parses
1055 layer specification strings (which is also used to decode the PERLIO
1056 environment variable) treats the colon as a separator.
1058 An unset or empty PERLIO is equivalent to the default set of layers for
1059 your platform, for example C<:unix:perlio> on UNIX-like systems
1060 and C<:unix:crlf> on Windows and other DOS-like systems.
1062 The list becomes the default for I<all> perl's IO. Consequently only built-in
1063 layers can appear in this list, as external layers (such as :encoding()) need
1064 IO in order to load them!. See L<"open pragma"|open> for how to add external
1065 encodings as defaults.
1067 The layers that it makes sense to include in the PERLIO environment
1068 variable are briefly summarised below. For more details see L<PerlIO>.
1075 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
1076 Unlikely to be useful on its own in the global PERLIO environment variable.
1077 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1082 A layer which does CRLF to "\n" translation distinguishing "text" and
1083 "binary" files in the manner of MS-DOS and similar operating systems.
1084 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1085 as being an end-of-file marker.)
1090 A layer which implements "reading" of files by using C<mmap()> to
1091 make (whole) file appear in the process's address space, and then
1092 using that as PerlIO's "buffer".
1097 This is a re-implementation of "stdio-like" buffering written as a
1098 PerlIO "layer". As such it will call whatever layer is below it for
1099 its operations (typically C<:unix>).
1104 An experimental pseudolayer that removes the topmost layer.
1105 Use with the same care as is reserved for nitroglycerin.
1110 A pseudolayer that manipulates other layers. Applying the C<:raw>
1111 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1112 pass each byte as-is without any translation. In particular CRLF
1113 translation, and/or :utf8 intuited from locale are disabled.
1115 Unlike in the earlier versions of Perl C<:raw> is I<not>
1116 just the inverse of C<:crlf> - other layers which would affect the
1117 binary nature of the stream are also removed or disabled.
1122 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1123 library calls. The layer provides both buffering and IO.
1124 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1125 is platforms normal behaviour. You will need a C<:crlf> layer above it
1131 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1136 A pseudolayer that turns on a flag on the layer below to tell perl
1137 that output should be in utf8 and that input should be regarded as
1138 already in utf8 form. May be useful in PERLIO environment
1139 variable to make UTF-8 the default. (To turn off that behaviour
1140 use C<:bytes> layer.)
1145 On Win32 platforms this I<experimental> layer uses native "handle" IO
1146 rather than unix-like numeric file descriptor layer. Known to be
1147 buggy in this release.
1151 On all platforms the default set of layers should give acceptable results.
1153 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1154 Configure is setup to prefer "stdio" implementation if system's library
1155 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1158 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1159 has a number of bugs/mis-features for perl IO which are somewhat
1160 C compiler vendor/version dependent. Using our own C<crlf> layer as
1161 the buffer avoids those issues and makes things more uniform.
1162 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1165 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1166 compiler's numeric file descriptor routines. There is an experimental native
1167 C<win32> layer which is expected to be enhanced and should eventually be
1168 the default under Win32.
1173 If set to the name of a file or device then certain operations of PerlIO
1174 sub-system will be logged to that file (opened as append). Typical uses
1177 PERLIO_DEBUG=/dev/tty perl script ...
1179 and Win32 approximate equivalent:
1181 set PERLIO_DEBUG=CON
1184 This functionality is disabled for setuid scripts and for scripts run
1190 A list of directories in which to look for Perl library
1191 files before looking in the standard library and the current directory.
1192 If PERL5LIB is defined, PERLLIB is not used.
1197 The command used to load the debugger code. The default is:
1199 BEGIN { require 'perl5db.pl' }
1201 =item PERL5DB_THREADED
1204 If set to a true value, indicates to the debugger that the code being
1205 debugged uses threads.
1207 =item PERL5SHELL (specific to the Win32 port)
1210 May be set to an alternative shell that perl must use internally for
1211 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1212 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1213 to be space-separated. Precede any character that needs to be protected
1214 (like a space or backslash) with a backslash.
1216 Note that Perl doesn't use COMSPEC for this purpose because
1217 COMSPEC has a high degree of variability among users, leading to
1218 portability concerns. Besides, perl can use a shell that may not be
1219 fit for interactive use, and setting COMSPEC to such a shell may
1220 interfere with the proper functioning of other programs (which usually
1221 look in COMSPEC to find a shell fit for interactive use).
1223 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1224 X<PERL_ALLOW_NON_IFS_LSP>
1226 Set to 1 to allow the use of non-IFS compatible LSP's.
1227 Perl normally searches for an IFS-compatible LSP because this is required
1228 for its emulation of Windows sockets as real filehandles. However, this may
1229 cause problems if you have a firewall such as McAfee Guardian which requires
1230 all applications to use its LSP which is not IFS-compatible, because clearly
1231 Perl will normally avoid using such an LSP.
1232 Setting this environment variable to 1 means that Perl will simply use the
1233 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1234 happy (and in that particular case Perl still works too because McAfee
1235 Guardian's LSP actually plays some other games which allow applications
1236 requiring IFS compatibility to work).
1238 =item PERL_DEBUG_MSTATS
1239 X<PERL_DEBUG_MSTATS>
1241 Relevant only if perl is compiled with the malloc included with the perl
1242 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1243 If set, this causes memory statistics to be dumped after execution. If set
1244 to an integer greater than one, also causes memory statistics to be dumped
1247 =item PERL_DESTRUCT_LEVEL
1248 X<PERL_DESTRUCT_LEVEL>
1250 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1251 this controls the behavior of global destruction of objects and other
1252 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1254 =item PERL_DL_NONLAZY
1257 Set to one to have perl resolve B<all> undefined symbols when it loads
1258 a dynamic library. The default behaviour is to resolve symbols when
1259 they are used. Setting this variable is useful during testing of
1260 extensions as it ensures that you get an error on misspelled function
1261 names even if the test suite doesn't call it.
1266 If using the C<encoding> pragma without an explicit encoding name, the
1267 PERL_ENCODING environment variable is consulted for an encoding name.
1269 =item PERL_HASH_SEED
1272 (Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
1273 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1274 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1275 things, that hash keys will be ordered the same between different runs
1278 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1279 If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1280 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1282 If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
1283 the pseudorandom seed supplied by the operating system and libraries.
1284 This means that each different run of Perl will have a different
1285 ordering of the results of keys(), values(), and each().
1287 B<Please note that the hash seed is sensitive information>. Hashes are
1288 randomized to protect against local and remote attacks against Perl
1289 code. By manually setting a seed this protection may be partially or
1292 See L<perlsec/"Algorithmic Complexity Attacks"> and
1293 L</PERL_HASH_SEED_DEBUG> for more information.
1295 =item PERL_HASH_SEED_DEBUG
1296 X<PERL_HASH_SEED_DEBUG>
1298 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1299 the hash seed at the beginning of execution. This, combined with
1300 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1301 behavior caused by hash randomization.
1303 B<Note that the hash seed is sensitive information>: by knowing it one
1304 can craft a denial-of-service attack against Perl code, even remotely,
1305 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1306 B<Do not disclose the hash seed> to people who don't need to know it.
1307 See also hash_seed() of L<Hash::Util>.
1309 =item PERL_ROOT (specific to the VMS port)
1312 A translation concealed rooted logical name that contains perl and the
1313 logical device for the @INC path on VMS only. Other logical names that
1314 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1315 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1316 L<perlvms> and in F<README.vms> in the Perl source distribution.
1321 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1322 signals behaviour (immediate but unsafe) is restored. If set to
1323 C<safe> the safe (or deferred) signals are used.
1324 See L<perlipc/"Deferred Signals (Safe Signals)">.
1329 Equivalent to the B<-C> command-line switch. Note that this is not
1330 a boolean variable-- setting this to C<"1"> is not the right way to
1331 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1332 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1333 your shell before starting Perl). See the description of the C<-C>
1334 switch for more information.
1336 =item SYS$LOGIN (specific to the VMS port)
1339 Used if chdir has no argument and HOME and LOGDIR are not set.
1343 Perl also has environment variables that control how Perl handles data
1344 specific to particular natural languages. See L<perllocale>.
1346 Apart from these, Perl uses no other environment variables, except
1347 to make them available to the program being executed, and to child
1348 processes. However, programs running setuid would do well to execute
1349 the following lines before doing anything else, just to keep people
1352 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1353 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1354 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};