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...'> ]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
17 S<[ B<-A [I<assertions>] >]>
18 S<[ B<-C [I<number/list>] >]>
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> 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
114 Unix's #! technique can be simulated on other systems:
122 extproc perl -S -your_switches
124 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
129 Create a batch file to run your program, and codify it in
130 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
131 distribution for more information).
135 The Win95/NT installation, when using the ActiveState installer for Perl,
136 will modify the Registry to associate the F<.pl> extension with the perl
137 interpreter. If you install Perl by other means (including building from
138 the sources), you may have to modify the Registry yourself. Note that
139 this means you can no longer tell the difference between an executable
140 Perl program and a Perl library file.
144 Under "Classic" MacOS, a perl program will have the appropriate Creator and
145 Type, so that double-clicking them will invoke the MacPerl application.
146 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
147 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
153 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
154 $ exit++ + ++$status != 0 and $exit = $status = undef;
156 at the top of your program, where B<-mysw> are any command line switches you
157 want to pass to Perl. You can now invoke the program directly, by saying
158 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
159 via F<DCL$PATH> by just using the name of the program).
161 This incantation is a bit much to remember, but Perl will display it for
162 you if you say C<perl "-V:startperl">.
166 Command-interpreters on non-Unix systems have rather different ideas
167 on quoting than Unix shells. You'll need to learn the special
168 characters in your command-interpreter (C<*>, C<\> and C<"> are
169 common) and how to protect whitespace and these characters to run
170 one-liners (see B<-e> below).
172 On some systems, you may have to change single-quotes to double ones,
173 which you must I<not> do on Unix or Plan 9 systems. You might also
174 have to change a single % to a %%.
179 perl -e 'print "Hello world\n"'
182 perl -e "print \"Hello world\n\""
185 print "Hello world\n"
186 (then Run "Myscript" or Shift-Command-R)
189 perl -e "print ""Hello world\n"""
191 The problem is that none of this is reliable: it depends on the
192 command and it is entirely possible neither works. If B<4DOS> were
193 the command shell, this would probably work better:
195 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
197 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
198 when nobody was looking, but just try to find documentation for its
201 Under the Macintosh, it depends which environment you are using. The MacPerl
202 shell, or MPW, is much like Unix shells in its support for several
203 quoting variants, except that it makes free use of the Macintosh's non-ASCII
204 characters as control characters.
206 There is no general solution to all of this. It's just a mess.
208 =head2 Location of Perl
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
231 As with all standard commands, a single-character switch may be
232 clustered with the following switch, if any.
234 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
240 =item B<-0>[I<octal/hexadecimal>]
242 specifies the input record separator (C<$/>) as an octal or
243 hexadecimal number. If there are no digits, the null character is the
244 separator. Other switches may precede or follow the digits. For
245 example, if you have a version of B<find> which can print filenames
246 terminated by the null character, you can say this:
248 find . -name '*.orig' -print0 | perl -n0e unlink
250 The special value 00 will cause Perl to slurp files in paragraph mode.
251 The value 0777 will cause Perl to slurp files whole because there is no
252 legal byte with that value.
254 If you want to specify any Unicode character, use the hexadecimal
255 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
256 (This means that you cannot use the C<-x> with a directory name that
257 consists of hexadecimal digits.)
259 =item B<-A [I<assertions>]>
261 Activates the assertions given after the switch as a comma-separated
262 list of assertion names. If no assertion name is given, activates all
263 assertions. See L<assertions>.
267 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
268 split command to the @F array is done as the first thing inside the
269 implicit while loop produced by the B<-n> or B<-p>.
271 perl -ane 'print pop(@F), "\n";'
280 An alternate delimiter may be specified using B<-F>.
282 =item B<-C [I<number/list>]>
284 The C<-C> flag controls some Unicode of the Perl Unicode features.
286 As of 5.8.1, the C<-C> can be followed either by a number or a list
287 of option letters. The letters, their numeric values, and effects
288 are as follows; listing the letters is equal to summing the numbers.
290 I 1 STDIN is assumed to be in UTF-8
291 O 2 STDOUT will be in UTF-8
292 E 4 STDERR will be in UTF-8
294 i 8 UTF-8 is the default PerlIO layer for input streams
295 o 16 UTF-8 is the default PerlIO layer for output streams
297 A 32 the @ARGV elements are expected to be strings encoded
299 L 64 normally the "IOEioA" are unconditional,
300 the L makes them conditional on the locale environment
301 variables (the LC_ALL, LC_TYPE, and LANG, in the order
302 of decreasing precedence) -- if the variables indicate
303 UTF-8, then the selected "IOEioA" are in effect
305 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
306 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
309 The C<io> options mean that any subsequent open() (or similar I/O
310 operations) will have the C<:utf8> PerlIO layer implicitly applied
311 to them, in other words, UTF-8 is expected from any input stream,
312 and UTF-8 is produced to any output stream. This is just the default,
313 with explicit layers in open() and with binmode() one can manipulate
316 C<-C> on its own (not followed by any number or option list), or the
317 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
318 same effect as C<-CSDL>. In other words, the standard I/O handles and
319 the default C<open()> layer are UTF-8-fied B<but> only if the locale
320 environment variables indicate a UTF-8 locale. This behaviour follows
321 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
323 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
324 disable all the above Unicode features.
326 The read-only magic variable C<${^UNICODE}> reflects the numeric value
327 of this setting. This is variable is set during Perl startup and is
328 thereafter read-only. If you want runtime effects, use the three-arg
329 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
330 and the C<open> pragma (see L<open>).
332 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
333 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
334 This feature was practically unused, however, and the command line
335 switch was therefore "recycled".)
339 causes Perl to check the syntax of the program and then exit without
340 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
341 C<use> blocks, because these are considered as occurring outside the
342 execution of your program. C<INIT> and C<END> blocks, however, will
349 runs the program under the Perl debugger. See L<perldebug>.
350 If B<t> is specified, it indicates to the debugger that threads
351 will be used in the code being debugged.
353 =item B<-d:>I<foo[=bar,baz]>
355 =item B<-dt:>I<foo[=bar,baz]>
357 runs the program under the control of a debugging, profiling, or
358 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
359 the program using the Devel::DProf profiler. As with the B<-M>
360 flag, options may be passed to the Devel::foo package where they
361 will be received and interpreted by the Devel::foo::import routine.
362 The comma-separated list of options must follow a C<=> character.
363 If B<t> is specified, it indicates to the debugger that threads
364 will be used in the code being debugged.
367 =item B<-D>I<letters>
371 sets debugging flags. To watch how it executes your program, use
372 B<-Dtls>. (This works only if debugging is compiled into your
373 Perl.) Another nice value is B<-Dx>, which lists your compiled
374 syntax tree. And B<-Dr> displays compiled regular expressions;
375 the format of the output is explained in L<perldebguts>.
377 As an alternative, specify a number instead of list of letters (e.g.,
378 B<-D14> is equivalent to B<-Dtls>):
380 1 p Tokenizing and parsing (with v, displays parse stack)
381 2 s Stack snapshots (with v, displays all stacks)
382 4 l Context (loop) stack processing
384 16 o Method and overloading resolution
385 32 c String/numeric conversions
386 64 P Print profiling info, preprocessor command for -P, source file input state
387 128 m Memory allocation
388 256 f Format processing
389 512 r Regular expression parsing and execution
390 1024 x Syntax tree dump
391 2048 u Tainting checks
392 4096 (Obsolete, previously used for LEAKTEST)
393 8192 H Hash dump -- usurps values()
394 16384 X Scratchpad allocation
396 65536 S Thread synchronization
398 262144 R Include reference counts of dumped variables (eg when using -Ds)
399 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
400 1048576 v Verbose: use in conjunction with other flags
401 2097152 C Copy On Write
402 4194304 A Consistency checks on internal structures
403 8388608 q quiet - currently only suppresses the "EXECUTING" message
405 All these flags require B<-DDEBUGGING> when you compile the Perl
406 executable (but see L<Devel::Peek>, L<re> which may change this).
407 See the F<INSTALL> file in the Perl source distribution
408 for how to do this. This flag is automatically set if you include B<-g>
409 option when C<Configure> asks you about optimizer/debugger flags.
411 If you're just trying to get a print out of each line of Perl code
412 as it executes, the way that C<sh -x> provides for shell scripts,
413 you can't use Perl's B<-D> switch. Instead do this
415 # If you have "env" utility
416 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
418 # Bourne shell syntax
419 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
422 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
424 See L<perldebug> for details and variations.
426 =item B<-e> I<commandline>
428 may be used to enter one line of program. If B<-e> is given, Perl
429 will not look for a filename in the argument list. Multiple B<-e>
430 commands may be given to build up a multi-line script. Make sure
431 to use semicolons where you would in a normal program.
433 =item B<-F>I<pattern>
435 specifies the pattern to split on if B<-a> is also in effect. The
436 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
437 put in single quotes.
441 prints a summary of the options.
443 =item B<-i>[I<extension>]
445 specifies that files processed by the C<E<lt>E<gt>> construct are to be
446 edited in-place. It does this by renaming the input file, opening the
447 output file by the original name, and selecting that output file as the
448 default for print() statements. The extension, if supplied, is used to
449 modify the name of the old file to make a backup copy, following these
452 If no extension is supplied, no backup is made and the current file is
455 If the extension doesn't contain a C<*>, then it is appended to the
456 end of the current filename as a suffix. If the extension does
457 contain one or more C<*> characters, then each C<*> is replaced
458 with the current filename. In Perl terms, you could think of this
461 ($backup = $extension) =~ s/\*/$file_name/g;
463 This allows you to add a prefix to the backup file, instead of (or in
464 addition to) a suffix:
466 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
468 Or even to place backup copies of the original files into another
469 directory (provided the directory already exists):
471 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
473 These sets of one-liners are equivalent:
475 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
476 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
478 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
479 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
481 From the shell, saying
483 $ perl -p -i.orig -e "s/foo/bar/; ... "
485 is the same as using the program:
487 #!/usr/bin/perl -pi.orig
490 which is equivalent to
493 $extension = '.orig';
495 if ($ARGV ne $oldargv) {
496 if ($extension !~ /\*/) {
497 $backup = $ARGV . $extension;
500 ($backup = $extension) =~ s/\*/$ARGV/g;
502 rename($ARGV, $backup);
503 open(ARGVOUT, ">$ARGV");
510 print; # this prints to original filename
514 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
515 know when the filename has changed. It does, however, use ARGVOUT for
516 the selected filehandle. Note that STDOUT is restored as the default
517 output filehandle after the loop.
519 As shown above, Perl creates the backup file whether or not any output
520 is actually changed. So this is just a fancy way to copy files:
522 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
524 $ perl -p -i'.orig' -e 1 file1 file2 file3...
526 You can use C<eof> without parentheses to locate the end of each input
527 file, in case you want to append to each file, or reset line numbering
528 (see example in L<perlfunc/eof>).
530 If, for a given file, Perl is unable to create the backup file as
531 specified in the extension then it will skip that file and continue on
532 with the next one (if it exists).
534 For a discussion of issues surrounding file permissions and B<-i>,
535 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?>.
537 You cannot use B<-i> to create directories or to strip extensions from
540 Perl does not expand C<~> in filenames, which is good, since some
541 folks use it for their backup files:
543 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
545 Note that because B<-i> renames or deletes the original file before
546 creating a new file of the same name, UNIX-style soft and hard links will
549 Finally, the B<-i> switch does not impede execution when no
550 files are given on the command line. In this case, no backup is made
551 (the original file cannot, of course, be determined) and processing
552 proceeds from STDIN to STDOUT as might be expected.
554 =item B<-I>I<directory>
556 Directories specified by B<-I> are prepended to the search path for
557 modules (C<@INC>), and also tells the C preprocessor where to search for
558 include files. The C preprocessor is invoked with B<-P>; by default it
559 searches /usr/include and /usr/lib/perl.
561 =item B<-l>[I<octnum>]
563 enables automatic line-ending processing. It has two separate
564 effects. First, it automatically chomps C<$/> (the input record
565 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
566 (the output record separator) to have the value of I<octnum> so
567 that any print statements will have that separator added back on.
568 If I<octnum> is omitted, sets C<$\> to the current value of
569 C<$/>. For instance, to trim lines to 80 columns:
571 perl -lpe 'substr($_, 80) = ""'
573 Note that the assignment C<$\ = $/> is done when the switch is processed,
574 so the input record separator can be different than the output record
575 separator if the B<-l> switch is followed by a B<-0> switch:
577 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
579 This sets C<$\> to newline and then sets C<$/> to the null character.
581 =item B<-m>[B<->]I<module>
583 =item B<-M>[B<->]I<module>
585 =item B<-M>[B<->]I<'module ...'>
587 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
589 B<-m>I<module> executes C<use> I<module> C<();> before executing your
592 B<-M>I<module> executes C<use> I<module> C<;> before executing your
593 program. You can use quotes to add extra code after the module name,
594 e.g., C<'-Mmodule qw(foo bar)'>.
596 If the first character after the B<-M> or B<-m> is a dash (C<->)
597 then the 'use' is replaced with 'no'.
599 A little builtin syntactic sugar means you can also say
600 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
601 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
602 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
603 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
604 removes the distinction between B<-m> and B<-M>.
608 causes Perl to assume the following loop around your program, which
609 makes it iterate over filename arguments somewhat like B<sed -n> or
614 ... # your program goes here
617 Note that the lines are not printed by default. See B<-p> to have
618 lines printed. If a file named by an argument cannot be opened for
619 some reason, Perl warns you about it and moves on to the next file.
621 Here is an efficient way to delete all files that haven't been modified for
624 find . -mtime +7 -print | perl -nle unlink
626 This is faster than using the B<-exec> switch of B<find> because you don't
627 have to start a process on every filename found. It does suffer from
628 the bug of mishandling newlines in pathnames, which you can fix if
629 you follow the example under B<-0>.
631 C<BEGIN> and C<END> blocks may be used to capture control before or after
632 the implicit program loop, just as in B<awk>.
636 causes Perl to assume the following loop around your program, which
637 makes it iterate over filename arguments somewhat like B<sed>:
642 ... # your program goes here
644 print or die "-p destination: $!\n";
647 If a file named by an argument cannot be opened for some reason, Perl
648 warns you about it, and moves on to the next file. Note that the
649 lines are printed automatically. An error occurring during printing is
650 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
651 overrides a B<-n> switch.
653 C<BEGIN> and C<END> blocks may be used to capture control before or after
654 the implicit loop, just as in B<awk>.
658 B<NOTE: Use of -P is strongly discouraged because of its inherent
659 problems, including poor portability.>
661 This option causes your program to be run through the C preprocessor before
662 compilation by Perl. Because both comments and B<cpp> directives begin
663 with the # character, you should avoid starting comments with any words
664 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
666 If you're considering using C<-P>, you might also want to look at the
667 Filter::cpp module from CPAN.
669 The problems of -P include, but are not limited to:
675 The C<#!> line is stripped, so any switches there don't apply.
679 A C<-P> on a C<#!> line doesn't work.
683 B<All> lines that begin with (whitespace and) a C<#> but
684 do not look like cpp commands, are stripped, including anything
685 inside Perl strings, regular expressions, and here-docs .
689 In some platforms the C preprocessor knows too much: it knows about
690 the C++ -style until-end-of-line comments starting with C<"//">.
691 This will cause problems with common Perl constructs like
695 because after -P this will became illegal code
699 The workaround is to use some other quoting separator than C<"/">,
700 like for example C<"!">:
708 It requires not only a working C preprocessor but also a working
709 F<sed>. If not on UNIX, you are probably out of luck on this.
713 Script line numbers are not preserved.
717 The C<-x> does not work with C<-P>.
723 enables rudimentary switch parsing for switches on the command
724 line after the program name but before any filename arguments (or before
725 an argument of B<-->). This means you can have switches with two leading
726 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
727 corresponding variable in the Perl program. The following program
728 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
729 if it is invoked with B<-xyz=abc>.
732 if ($xyz) { print "$xyz\n" }
734 Do note that B<--help> creates the variable ${-help}, which is not compliant
735 with C<strict refs>. Also, when using this option on a script with
736 warnings enabled you may get a lot of spurious "used only once" warnings.
740 makes Perl use the PATH environment variable to search for the
741 program (unless the name of the program contains directory separators).
743 On some platforms, this also makes Perl append suffixes to the
744 filename while searching for it. For example, on Win32 platforms,
745 the ".bat" and ".cmd" suffixes are appended if a lookup for the
746 original name fails, and if the name does not already end in one
747 of those suffixes. If your Perl was compiled with DEBUGGING turned
748 on, using the -Dp switch to Perl shows how the search progresses.
750 Typically this is used to emulate #! startup on platforms that don't
751 support #!. Its also convenient when debugging a script that uses #!,
752 and is thus normally found by the shell's $PATH search mechanism.
754 This example works on many platforms that have a shell compatible with
758 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
759 if $running_under_some_shell;
761 The system ignores the first line and feeds the program to F</bin/sh>,
762 which proceeds to try to execute the Perl program as a shell script.
763 The shell executes the second line as a normal shell command, and thus
764 starts up the Perl interpreter. On some systems $0 doesn't always
765 contain the full pathname, so the B<-S> tells Perl to search for the
766 program if necessary. After Perl locates the program, it parses the
767 lines and ignores them because the variable $running_under_some_shell
768 is never true. If the program will be interpreted by csh, you will need
769 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
770 embedded spaces (and such) in the argument list. To start up sh rather
771 than csh, some systems may have to replace the #! line with a line
772 containing just a colon, which will be politely ignored by Perl. Other
773 systems can't control that, and need a totally devious construct that
774 will work under any of B<csh>, B<sh>, or Perl, such as the following:
776 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
777 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
778 if $running_under_some_shell;
780 If the filename supplied contains directory separators (i.e., is an
781 absolute or relative pathname), and if that file is not found,
782 platforms that append file extensions will do so and try to look
783 for the file with those extensions added, one by one.
785 On DOS-like platforms, if the program does not contain directory
786 separators, it will first be searched for in the current directory
787 before being searched for on the PATH. On Unix platforms, the
788 program will be searched for strictly on the PATH.
792 Like B<-T>, but taint checks will issue warnings rather than fatal
793 errors. These warnings can be controlled normally with C<no warnings
796 B<NOTE: this is not a substitute for -T.> This is meant only to be
797 used as a temporary development aid while securing legacy code:
798 for real production code and for new secure code written from scratch
799 always use the real B<-T>.
803 forces "taint" checks to be turned on so you can test them. Ordinarily
804 these checks are done only when running setuid or setgid. It's a
805 good idea to turn them on explicitly for programs that run on behalf
806 of someone else whom you might not necessarily trust, such as CGI
807 programs or any internet servers you might write in Perl. See
808 L<perlsec> for details. For security reasons, this option must be
809 seen by Perl quite early; usually this means it must appear early
810 on the command line or in the #! line for systems which support
815 This obsolete switch causes Perl to dump core after compiling your
816 program. You can then in theory take this core dump and turn it
817 into an executable file by using the B<undump> program (not supplied).
818 This speeds startup at the expense of some disk space (which you
819 can minimize by stripping the executable). (Still, a "hello world"
820 executable comes out to about 200K on my machine.) If you want to
821 execute a portion of your program before dumping, use the dump()
822 operator instead. Note: availability of B<undump> is platform
823 specific and may not be available for a specific port of Perl.
825 This switch has been superseded in favor of the new Perl code
826 generator backends to the compiler. See L<B> and L<B::Bytecode>
831 allows Perl to do unsafe operations. Currently the only "unsafe"
832 operations are the unlinking of directories while running as superuser,
833 and running setuid programs with fatal taint checks turned into
834 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
835 be used along with this option to actually I<generate> the
836 taint-check warnings.
840 prints the version and patchlevel of your perl executable.
844 prints summary of the major perl configuration values and the current
847 =item B<-V:>I<configvar>
849 Prints to STDOUT the value of the named configuration variable(s),
850 with multiples when your configvar argument looks like a regex (has
851 non-letters). For example:
854 libc='/lib/libc-2.2.4.so';
856 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
857 libc='/lib/libc-2.2.4.so';
859 libpth='/usr/local/lib /lib /usr/lib';
860 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
862 libc='/lib/libc-2.2.4.so';
866 Additionally, extra colons can be used to control formatting. A
867 trailing colon suppresses the linefeed and terminator ';', allowing
868 you to embed queries into shell commands. (mnemonic: PATH separator
871 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
872 compression-vars: zcat='' zip='zip' are here !
874 A leading colon removes the 'name=' part of the response, this allows
875 you to map to the name you need. (mnemonic: empty label)
877 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
880 Leading and trailing colons can be used together if you need
881 positional parameter values without the names. Note that in the case
882 below, the PERL_API params are returned in alphabetical order.
884 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
885 building_on 'linux' '5' '1' '9' now
889 prints warnings about dubious constructs, such as variable names
890 that are mentioned only once and scalar variables that are used
891 before being set, redefined subroutines, references to undefined
892 filehandles or filehandles opened read-only that you are attempting
893 to write on, values used as a number that doesn't look like numbers,
894 using an array as though it were a scalar, if your subroutines
895 recurse more than 100 deep, and innumerable other things.
897 This switch really just enables the internal C<$^W> variable. You
898 can disable or promote into fatal errors specific warnings using
899 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
900 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
901 facility is also available if you want to manipulate entire classes
902 of warnings; see L<warnings> or L<perllexwarn>.
906 Enables all warnings regardless of C<no warnings> or C<$^W>.
911 Disables all warnings regardless of C<use warnings> or C<$^W>.
916 =item B<-x> I<directory>
918 tells Perl that the program is embedded in a larger chunk of unrelated
919 ASCII text, such as in a mail message. Leading garbage will be
920 discarded until the first line that starts with #! and contains the
921 string "perl". Any meaningful switches on that line will be applied.
922 If a directory name is specified, Perl will switch to that directory
923 before running the program. The B<-x> switch controls only the
924 disposal of leading garbage. The program must be terminated with
925 C<__END__> if there is trailing garbage to be ignored (the program
926 can process any or all of the trailing garbage via the DATA filehandle
937 Used if chdir has no argument.
941 Used if chdir has no argument and HOME is not set.
945 Used in executing subprocesses, and in finding the program if B<-S> is
950 A list of directories in which to look for Perl library
951 files before looking in the standard library and the current
952 directory. Any architecture-specific directories under the specified
953 locations are automatically included if they exist. If PERL5LIB is not
954 defined, PERLLIB is used. Directories are separated (like in PATH) by
955 a colon on unixish platforms and by a semicolon on Windows (the proper
956 path separator being given by the command C<perl -V:path_sep>).
958 When running taint checks (either because the program was running setuid
959 or setgid, or the B<-T> switch was used), neither variable is used.
960 The program should instead say:
962 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<-[DIMUdmtw]>
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.
975 A space (or colon) separated list of PerlIO layers. If perl is built
976 to use PerlIO system for IO (the default) these layers effect perl's IO.
978 It is conventional to start layer names with a colon e.g. C<:perlio> to
979 emphasise their similarity to variable "attributes". But the code that parses
980 layer specification strings (which is also used to decode the PERLIO
981 environment variable) treats the colon as a separator.
983 An unset or empty PERLIO is equivalent to C<:stdio>.
985 The list becomes the default for I<all> perl's IO. Consequently only built-in
986 layers can appear in this list, as external layers (such as :encoding()) need
987 IO in order to load them!. See L<"open pragma"|open> for how to add external
988 encodings as defaults.
990 The layers that it makes sense to include in the PERLIO environment
991 variable are briefly summarised below. For more details see L<PerlIO>.
997 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
998 Unlikely to be useful on its own in the global PERLIO environment variable.
999 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1003 A layer which does CRLF to "\n" translation distinguishing "text" and
1004 "binary" files in the manner of MS-DOS and similar operating systems.
1005 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1006 as being an end-of-file marker.)
1010 A layer which implements "reading" of files by using C<mmap()> to
1011 make (whole) file appear in the process's address space, and then
1012 using that as PerlIO's "buffer".
1016 This is a re-implementation of "stdio-like" buffering written as a
1017 PerlIO "layer". As such it will call whatever layer is below it for
1018 its operations (typically C<:unix>).
1022 An experimental pseudolayer that removes the topmost layer.
1023 Use with the same care as is reserved for nitroglycerin.
1027 A pseudolayer that manipulates other layers. Applying the C<:raw>
1028 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1029 pass each byte as-is without any translation. In particular CRLF
1030 translation, and/or :utf8 intuited from locale are disabled.
1032 Unlike in the earlier versions of Perl C<:raw> is I<not>
1033 just the inverse of C<:crlf> - other layers which would affect the
1034 binary nature of the stream are also removed or disabled.
1038 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1039 library calls. The layer provides both buffering and IO.
1040 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1041 is platforms normal behaviour. You will need a C<:crlf> layer above it
1046 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1050 A pseudolayer that turns on a flag on the layer below to tell perl
1051 that output should be in utf8 and that input should be regarded as
1052 already in utf8 form. May be useful in PERLIO environment
1053 variable to make UTF-8 the default. (To turn off that behaviour
1054 use C<:bytes> layer.)
1058 On Win32 platforms this I<experimental> layer uses native "handle" IO
1059 rather than unix-like numeric file descriptor layer. Known to be
1060 buggy in this release.
1064 On all platforms the default set of layers should give acceptable results.
1066 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1067 Configure is setup to prefer "stdio" implementation if system's library
1068 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1071 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1072 has a number of bugs/mis-features for perl IO which are somewhat
1073 C compiler vendor/version dependent. Using our own C<crlf> layer as
1074 the buffer avoids those issues and makes things more uniform.
1075 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1078 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1079 compiler's numeric file descriptor routines. There is an experimental native
1080 C<win32> layer which is expected to be enhanced and should eventually be
1081 the default under Win32.
1085 If set to the name of a file or device then certain operations of PerlIO
1086 sub-system will be logged to that file (opened as append). Typical uses
1089 PERLIO_DEBUG=/dev/tty perl script ...
1091 and Win32 approximate equivalent:
1093 set PERLIO_DEBUG=CON
1096 This functionality is disabled for setuid scripts and for scripts run
1101 A list of directories in which to look for Perl library
1102 files before looking in the standard library and the current directory.
1103 If PERL5LIB is defined, PERLLIB is not used.
1107 The command used to load the debugger code. The default is:
1109 BEGIN { require 'perl5db.pl' }
1111 =item PERL5DB_THREADED
1113 If set to a true value, indicates to the debugger that the code being
1114 debugged uses threads.
1116 =item PERL5SHELL (specific to the Win32 port)
1118 May be set to an alternative shell that perl must use internally for
1119 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1120 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1121 to be space-separated. Precede any character that needs to be protected
1122 (like a space or backslash) with a backslash.
1124 Note that Perl doesn't use COMSPEC for this purpose because
1125 COMSPEC has a high degree of variability among users, leading to
1126 portability concerns. Besides, perl can use a shell that may not be
1127 fit for interactive use, and setting COMSPEC to such a shell may
1128 interfere with the proper functioning of other programs (which usually
1129 look in COMSPEC to find a shell fit for interactive use).
1131 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1133 Set to 1 to allow the use of non-IFS compatible LSP's.
1134 Perl normally searches for an IFS-compatible LSP because this is required
1135 for its emulation of Windows sockets as real filehandles. However, this may
1136 cause problems if you have a firewall such as McAfee Guardian which requires
1137 all applications to use its LSP which is not IFS-compatible, because clearly
1138 Perl will normally avoid using such an LSP.
1139 Setting this environment variable to 1 means that Perl will simply use the
1140 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1141 happy (and in that particular case Perl still works too because McAfee
1142 Guardian's LSP actually plays some other games which allow applications
1143 requiring IFS compatibility to work).
1145 =item PERL_DEBUG_MSTATS
1147 Relevant only if perl is compiled with the malloc included with the perl
1148 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1149 If set, this causes memory statistics to be dumped after execution. If set
1150 to an integer greater than one, also causes memory statistics to be dumped
1153 =item PERL_DESTRUCT_LEVEL
1155 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1156 this controls the behavior of global destruction of objects and other
1157 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1159 =item PERL_DL_NONLAZY
1161 Set to one to have perl resolve B<all> undefined symbols when it loads
1162 a dynamic library. The default behaviour is to resolve symbols when
1163 they are used. Setting this variable is useful during testing of
1164 extensions as it ensures that you get an error on misspelled function
1165 names even if the test suite doesn't call it.
1169 If using the C<encoding> pragma without an explicit encoding name, the
1170 PERL_ENCODING environment variable is consulted for an encoding name.
1172 =item PERL_HASH_SEED
1174 (Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
1175 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1176 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1177 things, that hash keys will be ordered the same between different runs
1180 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1181 If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1182 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1184 If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
1185 the pseudorandom seed supplied by the operating system and libraries.
1186 This means that each different run of Perl will have a different
1187 ordering of the results of keys(), values(), and each().
1189 B<Please note that the hash seed is sensitive information>. Hashes are
1190 randomized to protect against local and remote attacks against Perl
1191 code. By manually setting a seed this protection may be partially or
1194 See L<perlsec/"Algorithmic Complexity Attacks"> and
1195 L</PERL_HASH_SEED_DEBUG> for more information.
1197 =item PERL_HASH_SEED_DEBUG
1199 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1200 the hash seed at the beginning of execution. This, combined with
1201 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1202 behavior caused by hash randomization.
1204 B<Note that the hash seed is sensitive information>: by knowing it one
1205 can craft a denial-of-service attack against Perl code, even remotely,
1206 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1207 B<Do not disclose the hash seed> to people who don't need to know it.
1208 See also hash_seed() of L<Hash::Util>.
1210 =item PERL_ROOT (specific to the VMS port)
1212 A translation concealed rooted logical name that contains perl and the
1213 logical device for the @INC path on VMS only. Other logical names that
1214 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1215 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1216 L<perlvms> and in F<README.vms> in the Perl source distribution.
1220 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1221 signals behaviour (immediate but unsafe) is restored. If set to
1222 C<safe> the safe (or deferred) signals are used.
1223 See L<perlipc/"Deferred Signals (Safe Signals)">.
1227 Equivalent to the B<-C> command-line switch. Note that this is not
1228 a boolean variable-- setting this to C<"1"> is not the right way to
1229 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1230 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1231 your shell before starting Perl). See the description of the C<-C>
1232 switch for more information.
1234 =item SYS$LOGIN (specific to the VMS port)
1236 Used if chdir has no argument and HOME and LOGDIR are not set.
1240 Perl also has environment variables that control how Perl handles data
1241 specific to particular natural languages. See L<perllocale>.
1243 Apart from these, Perl uses no other environment variables, except
1244 to make them available to the program being executed, and to child
1245 processes. However, programs running setuid would do well to execute
1246 the following lines before doing anything else, just to keep people
1249 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1250 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1251 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};