3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTtuUWX> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
12 S<[ B<-C [I<number/list>] >]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ [B<-e>|B<-E>] I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
20 The normal way to run a Perl program is by making it directly
21 executable, or else by passing the name of the source file as an
22 argument on the command line. (An interactive Perl environment
23 is also possible--see L<perldebug> for details on how to do that.)
24 Upon startup, Perl looks for your program in one of the following
31 Specified line by line via B<-e> or B<-E> switches on the command line.
35 Contained in the file specified by the first filename on the command line.
36 (Note that systems supporting the #! notation invoke interpreters this
37 way. See L<Location of Perl>.)
41 Passed in implicitly via standard input. This works only if there are
42 no filename arguments--to pass arguments to a STDIN-read program you
43 must explicitly specify a "-" for the program name.
47 With methods 2 and 3, Perl starts parsing the input file from the
48 beginning, unless you've specified a B<-x> switch, in which case it
49 scans for the first line starting with #! and containing the word
50 "perl", and starts there instead. This is useful for running a program
51 embedded in a larger message. (In this case you would indicate the end
52 of the program using the C<__END__> token.)
54 The #! line is always examined for switches as the line is being
55 parsed. Thus, if you're on a machine that allows only one argument
56 with the #! line, or worse, doesn't even recognize the #! line, you
57 still can get consistent switch behavior regardless of how Perl was
58 invoked, even if B<-x> was used to find the beginning of the program.
60 Because historically some operating systems silently chopped off
61 kernel interpretation of the #! line after 32 characters, some
62 switches may be passed in on the command line, and some may not;
63 you could even get a "-" without its letter, if you're not careful.
64 You probably want to make sure that all your switches fall either
65 before or after that 32-character boundary. Most switches don't
66 actually care if they're processed redundantly, but getting a "-"
67 instead of a complete switch could cause Perl to try to execute
68 standard input instead of your program. And a partial B<-I> switch
69 could also cause odd results.
71 Some switches do care if they are processed twice, for instance
72 combinations of B<-l> and B<-0>. Either put all the switches after
73 the 32-character boundary (if applicable), or replace the use of
74 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
76 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
77 The sequences "-*" and "- " are specifically ignored so that you could,
78 if you were so inclined, say
82 eval 'exec perl -x -wS $0 ${1+"$@"}'
85 to let Perl see the B<-p> switch.
87 A similar trick involves the B<env> program, if you have it.
91 The examples above use a relative path to the perl interpreter,
92 getting whatever version is first in the user's path. If you want
93 a specific version of Perl, say, perl5.005_57, you should place
94 that directly in the #! line's path.
96 If the #! line does not contain the word "perl", the program named after
97 the #! is executed instead of the Perl interpreter. This is slightly
98 bizarre, but it helps people on machines that don't do #!, because they
99 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
100 dispatch the program to the correct interpreter for them.
102 After locating your program, Perl compiles the entire program to an
103 internal form. If there are any compilation errors, execution of the
104 program is not attempted. (This is unlike the typical shell script,
105 which might run part-way through before finding a syntax error.)
107 If the program is syntactically correct, it is executed. If the program
108 runs off the end without hitting an exit() or die() operator, an implicit
109 C<exit(0)> is provided to indicate successful completion.
111 =head2 #! and quoting on non-Unix systems
114 Unix's #! technique can be simulated on other systems:
122 extproc perl -S -your_switches
124 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
129 Create a batch file to run your program, and codify it in
130 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
131 distribution for more information).
135 The Win95/NT installation, when using the ActiveState installer for Perl,
136 will modify the Registry to associate the F<.pl> extension with the perl
137 interpreter. If you install Perl by other means (including building from
138 the sources), you may have to modify the Registry yourself. Note that
139 this means you can no longer tell the difference between an executable
140 Perl program and a Perl library file.
144 Under "Classic" MacOS, a perl program will have the appropriate Creator and
145 Type, so that double-clicking them will invoke the MacPerl application.
146 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
147 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
153 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
154 $ exit++ + ++$status != 0 and $exit = $status = undef;
156 at the top of your program, where B<-mysw> are any command line switches you
157 want to pass to Perl. You can now invoke the program directly, by saying
158 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
159 via F<DCL$PATH> by just using the name of the program).
161 This incantation is a bit much to remember, but Perl will display it for
162 you if you say C<perl "-V:startperl">.
166 Command-interpreters on non-Unix systems have rather different ideas
167 on quoting than Unix shells. You'll need to learn the special
168 characters in your command-interpreter (C<*>, C<\> and C<"> are
169 common) and how to protect whitespace and these characters to run
170 one-liners (see B<-e> below).
172 On some systems, you may have to change single-quotes to double ones,
173 which you must I<not> do on Unix or Plan 9 systems. You might also
174 have to change a single % to a %%.
179 perl -e 'print "Hello world\n"'
182 perl -e "print \"Hello world\n\""
185 print "Hello world\n"
186 (then Run "Myscript" or Shift-Command-R)
189 perl -e "print ""Hello world\n"""
191 The problem is that none of this is reliable: it depends on the
192 command and it is entirely possible neither works. If B<4DOS> were
193 the command shell, this would probably work better:
195 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
197 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
198 when nobody was looking, but just try to find documentation for its
201 Under the Macintosh, it depends which environment you are using. The MacPerl
202 shell, or MPW, is much like Unix shells in its support for several
203 quoting variants, except that it makes free use of the Macintosh's non-ASCII
204 characters as control characters.
206 There is no general solution to all of this. It's just a mess.
208 =head2 Location of Perl
209 X<perl, location of interpreter>
211 It may seem obvious to say, but Perl is useful only when users can
212 easily find it. When possible, it's good for both F</usr/bin/perl>
213 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
214 that can't be done, system administrators are strongly encouraged
215 to put (symlinks to) perl and its accompanying utilities into a
216 directory typically found along a user's PATH, or in some other
217 obvious and convenient place.
219 In this documentation, C<#!/usr/bin/perl> on the first line of the program
220 will stand in for whatever method works on your system. You are
221 advised to use a specific path if you care about a specific version.
223 #!/usr/local/bin/perl5.00554
225 or if you just want to be running at least version, place a statement
226 like this at the top of your program:
230 =head2 Command Switches
231 X<perl, command switches> X<command switches>
233 As with all standard commands, a single-character switch may be
234 clustered with the following switch, if any.
236 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
242 =item B<-0>[I<octal/hexadecimal>]
245 specifies the input record separator (C<$/>) as an octal or
246 hexadecimal number. If there are no digits, the null character is the
247 separator. Other switches may precede or follow the digits. For
248 example, if you have a version of B<find> which can print filenames
249 terminated by the null character, you can say this:
251 find . -name '*.orig' -print0 | perl -n0e unlink
253 The special value 00 will cause Perl to slurp files in paragraph mode.
254 The value 0777 will cause Perl to slurp files whole because there is no
255 legal byte with that value.
257 If you want to specify any Unicode character, use the hexadecimal
258 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
259 (This means that you cannot use the C<-x> with a directory name that
260 consists of hexadecimal digits.)
265 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
266 split command to the @F array is done as the first thing inside the
267 implicit while loop produced by the B<-n> or B<-p>.
269 perl -ane 'print pop(@F), "\n";'
278 An alternate delimiter may be specified using B<-F>.
280 =item B<-C [I<number/list>]>
283 The C<-C> flag controls some of the Perl Unicode features.
285 As of 5.8.1, the C<-C> can be followed either by a number or a list
286 of option letters. The letters, their numeric values, and effects
287 are as follows; listing the letters is equal to summing the numbers.
289 I 1 STDIN is assumed to be in UTF-8
290 O 2 STDOUT will be in UTF-8
291 E 4 STDERR will be in UTF-8
293 i 8 UTF-8 is the default PerlIO layer for input streams
294 o 16 UTF-8 is the default PerlIO layer for output streams
296 A 32 the @ARGV elements are expected to be strings encoded
298 L 64 normally the "IOEioA" are unconditional,
299 the L makes them conditional on the locale environment
300 variables (the LC_ALL, LC_TYPE, and LANG, in the order
301 of decreasing precedence) -- if the variables indicate
302 UTF-8, then the selected "IOEioA" are in effect
303 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching code in
306 =for documenting_the_underdocumented
307 perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
310 perltodo mentions Unicode in %ENV and filenames. I guess that these will be
311 options e and f (or F).
313 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
314 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
317 The C<io> options mean that any subsequent open() (or similar I/O
318 operations) will have the C<:utf8> PerlIO layer implicitly applied
319 to them, in other words, UTF-8 is expected from any input stream,
320 and UTF-8 is produced to any output stream. This is just the default,
321 with explicit layers in open() and with binmode() one can manipulate
324 C<-C> on its own (not followed by any number or option list), or the
325 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
326 same effect as C<-CSDL>. In other words, the standard I/O handles and
327 the default C<open()> layer are UTF-8-fied B<but> only if the locale
328 environment variables indicate a UTF-8 locale. This behaviour follows
329 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
331 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
332 disable all the above Unicode features.
334 The read-only magic variable C<${^UNICODE}> reflects the numeric value
335 of this setting. This is variable is set during Perl startup and is
336 thereafter read-only. If you want runtime effects, use the three-arg
337 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
338 and the C<open> pragma (see L<open>).
340 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
341 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
342 This feature was practically unused, however, and the command line
343 switch was therefore "recycled".)
345 B<Note:> Since perl 5.10.1, if the -C option is used on the #! line, it
346 must be specified on the command line as well, since the standard streams
347 are already set up at this point in the execution of the perl interpreter.
348 You can also use binmode() to set the encoding of an I/O stream.
353 causes Perl to check the syntax of the program and then exit without
354 executing it. Actually, it I<will> execute C<BEGIN>, C<UNITCHECK>,
355 C<CHECK>, and C<use> blocks, because these are considered as occurring
356 outside the execution of your program. C<INIT> and C<END> blocks,
357 however, will be skipped.
364 runs the program under the Perl debugger. See L<perldebug>.
365 If B<t> is specified, it indicates to the debugger that threads
366 will be used in the code being debugged.
368 =item B<-d:>I<foo[=bar,baz]>
371 =item B<-dt:>I<foo[=bar,baz]>
373 runs the program under the control of a debugging, profiling, or
374 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
375 the program using the Devel::DProf profiler. As with the B<-M>
376 flag, options may be passed to the Devel::foo package where they
377 will be received and interpreted by the Devel::foo::import routine.
378 The comma-separated list of options must follow a C<=> character.
379 If B<t> is specified, it indicates to the debugger that threads
380 will be used in the code being debugged.
383 =item B<-D>I<letters>
384 X<-D> X<DEBUGGING> X<-DDEBUGGING>
388 sets debugging flags. To watch how it executes your program, use
389 B<-Dtls>. (This works only if debugging is compiled into your
390 Perl.) Another nice value is B<-Dx>, which lists your compiled
391 syntax tree. And B<-Dr> displays compiled regular expressions;
392 the format of the output is explained in L<perldebguts>.
394 As an alternative, specify a number instead of list of letters (e.g.,
395 B<-D14> is equivalent to B<-Dtls>):
397 1 p Tokenizing and parsing (with v, displays parse stack)
398 2 s Stack snapshots (with v, displays all stacks)
399 4 l Context (loop) stack processing
401 16 o Method and overloading resolution
402 32 c String/numeric conversions
403 64 P Print profiling info, source file input state
404 128 m Memory and SV allocation
405 256 f Format processing
406 512 r Regular expression parsing and execution
407 1024 x Syntax tree dump
408 2048 u Tainting checks
409 4096 U Unofficial, User hacking (reserved for private, unreleased use)
410 8192 H Hash dump -- usurps values()
411 16384 X Scratchpad allocation
414 262144 R Include reference counts of dumped variables (eg when using -Ds)
415 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
416 1048576 v Verbose: use in conjunction with other flags
417 2097152 C Copy On Write
418 4194304 A Consistency checks on internal structures
419 8388608 q quiet - currently only suppresses the "EXECUTING" message
420 16777216 M trace smart match resolution
422 All these flags require B<-DDEBUGGING> when you compile the Perl
423 executable (but see L<Devel::Peek>, L<re> which may change this).
424 See the F<INSTALL> file in the Perl source distribution
425 for how to do this. This flag is automatically set if you include B<-g>
426 option when C<Configure> asks you about optimizer/debugger flags.
428 If you're just trying to get a print out of each line of Perl code
429 as it executes, the way that C<sh -x> provides for shell scripts,
430 you can't use Perl's B<-D> switch. Instead do this
432 # If you have "env" utility
433 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
435 # Bourne shell syntax
436 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
439 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
441 See L<perldebug> for details and variations.
443 =item B<-e> I<commandline>
446 may be used to enter one line of program. If B<-e> is given, Perl
447 will not look for a filename in the argument list. Multiple B<-e>
448 commands may be given to build up a multi-line script. Make sure
449 to use semicolons where you would in a normal program.
451 =item B<-E> I<commandline>
454 behaves just like B<-e>, except that it implicitly enables all
455 optional features (in the main compilation unit). See L<feature>.
460 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
462 Perl can be built so that it by default will try to execute
463 F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block).
464 This is a hook that allows the sysadmin to customize how perl behaves.
465 It can for instance be used to add entries to the @INC array to make perl
466 find modules in non-standard locations.
468 =item B<-F>I<pattern>
471 specifies the pattern to split on if B<-a> is also in effect. The
472 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
473 put in single quotes. You can't use literal whitespace in the pattern.
478 prints a summary of the options.
480 =item B<-i>[I<extension>]
483 specifies that files processed by the C<E<lt>E<gt>> construct are to be
484 edited in-place. It does this by renaming the input file, opening the
485 output file by the original name, and selecting that output file as the
486 default for print() statements. The extension, if supplied, is used to
487 modify the name of the old file to make a backup copy, following these
490 If no extension is supplied, no backup is made and the current file is
493 If the extension doesn't contain a C<*>, then it is appended to the
494 end of the current filename as a suffix. If the extension does
495 contain one or more C<*> characters, then each C<*> is replaced
496 with the current filename. In Perl terms, you could think of this
499 ($backup = $extension) =~ s/\*/$file_name/g;
501 This allows you to add a prefix to the backup file, instead of (or in
502 addition to) a suffix:
504 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
506 Or even to place backup copies of the original files into another
507 directory (provided the directory already exists):
509 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
511 These sets of one-liners are equivalent:
513 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
514 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
516 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
517 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
519 From the shell, saying
521 $ perl -p -i.orig -e "s/foo/bar/; ... "
523 is the same as using the program:
525 #!/usr/bin/perl -pi.orig
528 which is equivalent to
531 $extension = '.orig';
533 if ($ARGV ne $oldargv) {
534 if ($extension !~ /\*/) {
535 $backup = $ARGV . $extension;
538 ($backup = $extension) =~ s/\*/$ARGV/g;
540 rename($ARGV, $backup);
541 open(ARGVOUT, ">$ARGV");
548 print; # this prints to original filename
552 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
553 know when the filename has changed. It does, however, use ARGVOUT for
554 the selected filehandle. Note that STDOUT is restored as the default
555 output filehandle after the loop.
557 As shown above, Perl creates the backup file whether or not any output
558 is actually changed. So this is just a fancy way to copy files:
560 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
562 $ perl -p -i'.orig' -e 1 file1 file2 file3...
564 You can use C<eof> without parentheses to locate the end of each input
565 file, in case you want to append to each file, or reset line numbering
566 (see example in L<perlfunc/eof>).
568 If, for a given file, Perl is unable to create the backup file as
569 specified in the extension then it will skip that file and continue on
570 with the next one (if it exists).
572 For a discussion of issues surrounding file permissions and B<-i>,
573 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?>.
575 You cannot use B<-i> to create directories or to strip extensions from
578 Perl does not expand C<~> in filenames, which is good, since some
579 folks use it for their backup files:
581 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
583 Note that because B<-i> renames or deletes the original file before
584 creating a new file of the same name, UNIX-style soft and hard links will
587 Finally, the B<-i> switch does not impede execution when no
588 files are given on the command line. In this case, no backup is made
589 (the original file cannot, of course, be determined) and processing
590 proceeds from STDIN to STDOUT as might be expected.
592 =item B<-I>I<directory>
595 Directories specified by B<-I> are prepended to the search path for
598 =item B<-l>[I<octnum>]
601 enables automatic line-ending processing. It has two separate
602 effects. First, it automatically chomps C<$/> (the input record
603 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
604 (the output record separator) to have the value of I<octnum> so
605 that any print statements will have that separator added back on.
606 If I<octnum> is omitted, sets C<$\> to the current value of
607 C<$/>. For instance, to trim lines to 80 columns:
609 perl -lpe 'substr($_, 80) = ""'
611 Note that the assignment C<$\ = $/> is done when the switch is processed,
612 so the input record separator can be different than the output record
613 separator if the B<-l> switch is followed by a B<-0> switch:
615 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
617 This sets C<$\> to newline and then sets C<$/> to the null character.
619 =item B<-m>[B<->]I<module>
622 =item B<-M>[B<->]I<module>
624 =item B<-M>[B<->]I<'module ...'>
626 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
628 B<-m>I<module> executes C<use> I<module> C<();> before executing your
631 B<-M>I<module> executes C<use> I<module> C<;> before executing your
632 program. You can use quotes to add extra code after the module name,
633 e.g., C<'-Mmodule qw(foo bar)'>.
635 If the first character after the B<-M> or B<-m> is a dash (C<->)
636 then the 'use' is replaced with 'no'.
638 A little builtin syntactic sugar means you can also say
639 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
640 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
641 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
642 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
643 removes the distinction between B<-m> and B<-M>.
645 A consequence of this is that B<-MFoo=number> never does a version check
646 (unless C<Foo::import()> itself is set up to do a version check, which
647 could happen for example if Foo inherits from Exporter.)
652 causes Perl to assume the following loop around your program, which
653 makes it iterate over filename arguments somewhat like B<sed -n> or
658 ... # your program goes here
661 Note that the lines are not printed by default. See B<-p> to have
662 lines printed. If a file named by an argument cannot be opened for
663 some reason, Perl warns you about it and moves on to the next file.
665 Also note that C<< <> >> passes command line arguments to
666 L<perlfunc/open>, which doesn't necessarily interpret them as file names.
667 See L<perlop> for possible security implications.
669 Here is an efficient way to delete all files that haven't been modified for
672 find . -mtime +7 -print | perl -nle unlink
674 This is faster than using the B<-exec> switch of B<find> because you don't
675 have to start a process on every filename found. It does suffer from
676 the bug of mishandling newlines in pathnames, which you can fix if
677 you follow the example under B<-0>.
679 C<BEGIN> and C<END> blocks may be used to capture control before or after
680 the implicit program loop, just as in B<awk>.
685 causes Perl to assume the following loop around your program, which
686 makes it iterate over filename arguments somewhat like B<sed>:
691 ... # your program goes here
693 print or die "-p destination: $!\n";
696 If a file named by an argument cannot be opened for some reason, Perl
697 warns you about it, and moves on to the next file. Note that the
698 lines are printed automatically. An error occurring during printing is
699 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
700 overrides a B<-n> switch.
702 C<BEGIN> and C<END> blocks may be used to capture control before or after
703 the implicit loop, just as in B<awk>.
708 enables rudimentary switch parsing for switches on the command
709 line after the program name but before any filename arguments (or before
710 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
711 corresponding variable in the Perl program. The following program
712 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
713 if it is invoked with B<-xyz=abc>.
716 if ($xyz) { print "$xyz\n" }
718 Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
719 with C<strict refs>. Also, when using this option on a script with
720 warnings enabled you may get a lot of spurious "used only once" warnings.
725 makes Perl use the PATH environment variable to search for the
726 program (unless the name of the program contains directory separators).
728 On some platforms, this also makes Perl append suffixes to the
729 filename while searching for it. For example, on Win32 platforms,
730 the ".bat" and ".cmd" suffixes are appended if a lookup for the
731 original name fails, and if the name does not already end in one
732 of those suffixes. If your Perl was compiled with DEBUGGING turned
733 on, using the -Dp switch to Perl shows how the search progresses.
735 Typically this is used to emulate #! startup on platforms that don't
736 support #!. Its also convenient when debugging a script that uses #!,
737 and is thus normally found by the shell's $PATH search mechanism.
739 This example works on many platforms that have a shell compatible with
743 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
744 if $running_under_some_shell;
746 The system ignores the first line and feeds the program to F</bin/sh>,
747 which proceeds to try to execute the Perl program as a shell script.
748 The shell executes the second line as a normal shell command, and thus
749 starts up the Perl interpreter. On some systems $0 doesn't always
750 contain the full pathname, so the B<-S> tells Perl to search for the
751 program if necessary. After Perl locates the program, it parses the
752 lines and ignores them because the variable $running_under_some_shell
753 is never true. If the program will be interpreted by csh, you will need
754 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
755 embedded spaces (and such) in the argument list. To start up sh rather
756 than csh, some systems may have to replace the #! line with a line
757 containing just a colon, which will be politely ignored by Perl. Other
758 systems can't control that, and need a totally devious construct that
759 will work under any of B<csh>, B<sh>, or Perl, such as the following:
761 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
762 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
763 if $running_under_some_shell;
765 If the filename supplied contains directory separators (i.e., is an
766 absolute or relative pathname), and if that file is not found,
767 platforms that append file extensions will do so and try to look
768 for the file with those extensions added, one by one.
770 On DOS-like platforms, if the program does not contain directory
771 separators, it will first be searched for in the current directory
772 before being searched for on the PATH. On Unix platforms, the
773 program will be searched for strictly on the PATH.
778 Like B<-T>, but taint checks will issue warnings rather than fatal
779 errors. These warnings can be controlled normally with C<no warnings
782 B<NOTE: this is not a substitute for -T.> This is meant only to be
783 used as a temporary development aid while securing legacy code:
784 for real production code and for new secure code written from scratch
785 always use the real B<-T>.
790 forces "taint" checks to be turned on so you can test them. Ordinarily
791 these checks are done only when running setuid or setgid. It's a
792 good idea to turn them on explicitly for programs that run on behalf
793 of someone else whom you might not necessarily trust, such as CGI
794 programs or any internet servers you might write in Perl. See
795 L<perlsec> for details. For security reasons, this option must be
796 seen by Perl quite early; usually this means it must appear early
797 on the command line or in the #! line for systems which support
803 This obsolete switch causes Perl to dump core after compiling your
804 program. You can then in theory take this core dump and turn it
805 into an executable file by using the B<undump> program (not supplied).
806 This speeds startup at the expense of some disk space (which you
807 can minimize by stripping the executable). (Still, a "hello world"
808 executable comes out to about 200K on my machine.) If you want to
809 execute a portion of your program before dumping, use the dump()
810 operator instead. Note: availability of B<undump> is platform
811 specific and may not be available for a specific port of Perl.
816 allows Perl to do unsafe operations. Currently the only "unsafe"
817 operations are attempting to unlink directories while running as
818 superuser, and running setuid programs with fatal taint checks turned
819 into warnings. Note that the B<-w> switch (or the C<$^W> variable)
820 must be used along with this option to actually I<generate> the
821 taint-check warnings.
826 prints the version and patchlevel of your perl executable.
831 prints summary of the major perl configuration values and the current
834 =item B<-V:>I<configvar>
836 Prints to STDOUT the value of the named configuration variable(s),
837 with multiples when your configvar argument looks like a regex (has
838 non-letters). For example:
841 libc='/lib/libc-2.2.4.so';
843 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
844 libc='/lib/libc-2.2.4.so';
846 libpth='/usr/local/lib /lib /usr/lib';
847 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
849 libc='/lib/libc-2.2.4.so';
853 Additionally, extra colons can be used to control formatting. A
854 trailing colon suppresses the linefeed and terminator ';', allowing
855 you to embed queries into shell commands. (mnemonic: PATH separator
858 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
859 compression-vars: zcat='' zip='zip' are here !
861 A leading colon removes the 'name=' part of the response, this allows
862 you to map to the name you need. (mnemonic: empty label)
864 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
867 Leading and trailing colons can be used together if you need
868 positional parameter values without the names. Note that in the case
869 below, the PERL_API params are returned in alphabetical order.
871 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
872 building_on 'linux' '5' '1' '9' now
877 prints warnings about dubious constructs, such as variable names
878 that are mentioned only once and scalar variables that are used
879 before being set, redefined subroutines, references to undefined
880 filehandles or filehandles opened read-only that you are attempting
881 to write on, values used as a number that don't look like numbers,
882 using an array as though it were a scalar, if your subroutines
883 recurse more than 100 deep, and innumerable other things.
885 This switch really just enables the internal C<$^W> variable. You
886 can disable or promote into fatal errors specific warnings using
887 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
888 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
889 facility is also available if you want to manipulate entire classes
890 of warnings; see L<warnings> or L<perllexwarn>.
895 Enables all warnings regardless of C<no warnings> or C<$^W>.
901 Disables all warnings regardless of C<use warnings> or C<$^W>.
907 =item B<-x>I<directory>
909 tells Perl that the program is embedded in a larger chunk of unrelated
910 ASCII text, such as in a mail message. Leading garbage will be
911 discarded until the first line that starts with #! and contains the
912 string "perl". Any meaningful switches on that line will be applied.
914 All references to line numbers by the program (warnings, errors, ...)
915 will treat the #! line as the first line.
916 Thus a warning on the 2nd line of the program (which is on the 100th
917 line in the file) will be reported as line 2, and not as line 100.
918 This can be overridden by using the #line directive.
919 (See L<perlsyn/"Plain-Old-Comments-(Not!)">)
921 If a directory name is specified, Perl will switch to that directory
922 before running the program. The B<-x> switch controls only the
923 disposal of leading garbage. The program must be terminated with
924 C<__END__> if there is trailing garbage to be ignored (the program
925 can process any or all of the trailing garbage via the DATA filehandle
928 The directory, if specified, must appear immediately following the B<-x>
929 with no intervening whitespace.
934 X<perl, environment variables>
941 Used if chdir has no argument.
946 Used if chdir has no argument and HOME is not set.
951 Used in executing subprocesses, and in finding the program if B<-S> is
957 A list of directories in which to look for Perl library
958 files before looking in the standard library and the current
959 directory. Any architecture-specific directories under the specified
960 locations are automatically included if they exist (this lookup
961 being done at interpreter startup time.)
963 If PERL5LIB is not defined, PERLLIB is used. Directories are separated
964 (like in PATH) by a colon on unixish platforms and by a semicolon on
965 Windows (the proper path separator being given by the command C<perl
968 When running taint checks (either because the program was running setuid
969 or setgid, or the B<-T> or B<-t> switch was specified), neither variable
970 is used. The program should instead say:
972 use lib "/my/directory";
977 Command-line options (switches). Switches in this variable are taken
978 as if they were on every Perl command line. Only the B<-[CDIMUdmtwW]>
979 switches are allowed. When running taint checks (because the program
980 was running setuid or setgid, or the B<-T> switch was used), this
981 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
982 enabled, and any subsequent options ignored.
987 A space (or colon) separated list of PerlIO layers. If perl is built
988 to use PerlIO system for IO (the default) these layers effect perl's IO.
990 It is conventional to start layer names with a colon e.g. C<:perlio> to
991 emphasise their similarity to variable "attributes". But the code that parses
992 layer specification strings (which is also used to decode the PERLIO
993 environment variable) treats the colon as a separator.
995 An unset or empty PERLIO is equivalent to the default set of layers for
996 your platform, for example C<:unix:perlio> on UNIX-like systems
997 and C<:unix:crlf> on Windows and other DOS-like systems.
999 The list becomes the default for I<all> perl's IO. Consequently only built-in
1000 layers can appear in this list, as external layers (such as :encoding()) need
1001 IO in order to load them!. See L<"open pragma"|open> for how to add external
1002 encodings as defaults.
1004 The layers that it makes sense to include in the PERLIO environment
1005 variable are briefly summarised below. For more details see L<PerlIO>.
1012 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
1013 Unlikely to be useful on its own in the global PERLIO environment variable.
1014 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1019 A layer which does CRLF to "\n" translation distinguishing "text" and
1020 "binary" files in the manner of MS-DOS and similar operating systems.
1021 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1022 as being an end-of-file marker.)
1027 A layer which implements "reading" of files by using C<mmap()> to
1028 make (whole) file appear in the process's address space, and then
1029 using that as PerlIO's "buffer".
1034 This is a re-implementation of "stdio-like" buffering written as a
1035 PerlIO "layer". As such it will call whatever layer is below it for
1036 its operations (typically C<:unix>).
1041 An experimental pseudolayer that removes the topmost layer.
1042 Use with the same care as is reserved for nitroglycerin.
1047 A pseudolayer that manipulates other layers. Applying the C<:raw>
1048 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1049 pass each byte as-is without any translation. In particular CRLF
1050 translation, and/or :utf8 intuited from locale are disabled.
1052 Unlike in the earlier versions of Perl C<:raw> is I<not>
1053 just the inverse of C<:crlf> - other layers which would affect the
1054 binary nature of the stream are also removed or disabled.
1059 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1060 library calls. The layer provides both buffering and IO.
1061 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1062 is platforms normal behaviour. You will need a C<:crlf> layer above it
1068 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1073 A pseudolayer that turns on a flag on the layer below to tell perl
1074 that output should be in utf8 and that input should be regarded as
1075 already in valid utf8 form. It does not check for validity and as such
1076 should be handled with caution for input. Generally C<:encoding(utf8)> is
1077 the best option when reading UTF-8 encoded data.
1082 On Win32 platforms this I<experimental> layer uses native "handle" IO
1083 rather than unix-like numeric file descriptor layer. Known to be
1084 buggy in this release.
1088 On all platforms the default set of layers should give acceptable results.
1090 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1091 Configure is setup to prefer "stdio" implementation if system's library
1092 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1095 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1096 has a number of bugs/mis-features for perl IO which are somewhat
1097 C compiler vendor/version dependent. Using our own C<crlf> layer as
1098 the buffer avoids those issues and makes things more uniform.
1099 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1102 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1103 compiler's numeric file descriptor routines. There is an experimental native
1104 C<win32> layer which is expected to be enhanced and should eventually be
1105 the default under Win32.
1107 The PERLIO environment variable is completely ignored when perl
1108 is run in taint mode.
1113 If set to the name of a file or device then certain operations of PerlIO
1114 sub-system will be logged to that file (opened as append). Typical uses
1117 PERLIO_DEBUG=/dev/tty perl script ...
1119 and Win32 approximate equivalent:
1121 set PERLIO_DEBUG=CON
1124 This functionality is disabled for setuid scripts and for scripts run
1130 A list of directories in which to look for Perl library
1131 files before looking in the standard library and the current directory.
1132 If PERL5LIB is defined, PERLLIB is not used.
1134 The PERLLIB environment variable is completely ignored when perl
1135 is run in taint mode.
1140 The command used to load the debugger code. The default is:
1142 BEGIN { require 'perl5db.pl' }
1144 The PERL5DB environment variable only used when perl is started with
1145 a bare B<-d> switch.
1147 =item PERL5DB_THREADED
1150 If set to a true value, indicates to the debugger that the code being
1151 debugged uses threads.
1153 =item PERL5SHELL (specific to the Win32 port)
1156 May be set to an alternative shell that perl must use internally for
1157 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1158 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1159 to be space-separated. Precede any character that needs to be protected
1160 (like a space or backslash) with a backslash.
1162 Note that Perl doesn't use COMSPEC for this purpose because
1163 COMSPEC has a high degree of variability among users, leading to
1164 portability concerns. Besides, perl can use a shell that may not be
1165 fit for interactive use, and setting COMSPEC to such a shell may
1166 interfere with the proper functioning of other programs (which usually
1167 look in COMSPEC to find a shell fit for interactive use).
1169 Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked
1170 when running external commands. It is recommended that
1171 you explicitly set (or delete) C<$ENV{PERL5SHELL}> when running
1172 in taint mode under Windows.
1174 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1175 X<PERL_ALLOW_NON_IFS_LSP>
1177 Set to 1 to allow the use of non-IFS compatible LSP's.
1178 Perl normally searches for an IFS-compatible LSP because this is required
1179 for its emulation of Windows sockets as real filehandles. However, this may
1180 cause problems if you have a firewall such as McAfee Guardian which requires
1181 all applications to use its LSP which is not IFS-compatible, because clearly
1182 Perl will normally avoid using such an LSP.
1183 Setting this environment variable to 1 means that Perl will simply use the
1184 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1185 happy (and in that particular case Perl still works too because McAfee
1186 Guardian's LSP actually plays some other games which allow applications
1187 requiring IFS compatibility to work).
1189 =item PERL_DEBUG_MSTATS
1190 X<PERL_DEBUG_MSTATS>
1192 Relevant only if perl is compiled with the malloc included with the perl
1193 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1194 If set, this causes memory statistics to be dumped after execution. If set
1195 to an integer greater than one, also causes memory statistics to be dumped
1198 =item PERL_DESTRUCT_LEVEL
1199 X<PERL_DESTRUCT_LEVEL>
1201 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1202 this controls the behavior of global destruction of objects and other
1203 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1205 =item PERL_DL_NONLAZY
1208 Set to one to have perl resolve B<all> undefined symbols when it loads
1209 a dynamic library. The default behaviour is to resolve symbols when
1210 they are used. Setting this variable is useful during testing of
1211 extensions as it ensures that you get an error on misspelled function
1212 names even if the test suite doesn't call it.
1217 If using the C<encoding> pragma without an explicit encoding name, the
1218 PERL_ENCODING environment variable is consulted for an encoding name.
1220 =item PERL_HASH_SEED
1223 (Since Perl 5.8.1.) Used to randomise perl's internal hash function.
1224 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1225 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1226 things, that hash keys will always have the same ordering between
1227 different runs of perl.
1229 Most hashes return elements in the same order as Perl 5.8.0 by default.
1230 On a hash by hash basis, if pathological data is detected during a hash
1231 key insertion, then that hash will switch to an alternative random hash
1234 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1235 If perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1236 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1238 If PERL_HASH_SEED is unset or set to a non-numeric string, perl uses
1239 the pseudorandom seed supplied by the operating system and libraries.
1241 B<Please note that the hash seed is sensitive information>. Hashes are
1242 randomized to protect against local and remote attacks against Perl
1243 code. By manually setting a seed this protection may be partially or
1246 See L<perlsec/"Algorithmic Complexity Attacks"> and
1247 L</PERL_HASH_SEED_DEBUG> for more information.
1249 =item PERL_HASH_SEED_DEBUG
1250 X<PERL_HASH_SEED_DEBUG>
1252 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1253 the hash seed at the beginning of execution. This, combined with
1254 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1255 behavior caused by hash randomization.
1257 B<Note that the hash seed is sensitive information>: by knowing it one
1258 can craft a denial-of-service attack against Perl code, even remotely,
1259 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1260 B<Do not disclose the hash seed> to people who don't need to know it.
1261 See also hash_seed() of L<Hash::Util>.
1263 =item PERL_ROOT (specific to the VMS port)
1266 A translation concealed rooted logical name that contains perl and the
1267 logical device for the @INC path on VMS only. Other logical names that
1268 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1269 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1270 L<perlvms> and in F<README.vms> in the Perl source distribution.
1275 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1276 signals behaviour (immediate but unsafe) is restored. If set to
1277 C<safe> the safe (or deferred) signals are used.
1278 See L<perlipc/"Deferred Signals (Safe Signals)">.
1283 Equivalent to the B<-C> command-line switch. Note that this is not
1284 a boolean variable-- setting this to C<"1"> is not the right way to
1285 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1286 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1287 your shell before starting Perl). See the description of the C<-C>
1288 switch for more information.
1290 =item SYS$LOGIN (specific to the VMS port)
1293 Used if chdir has no argument and HOME and LOGDIR are not set.
1297 Perl also has environment variables that control how Perl handles data
1298 specific to particular natural languages. See L<perllocale>.
1300 Apart from these, Perl uses no other environment variables, except
1301 to make them available to the program being executed, and to child
1302 processes. However, programs running setuid would do well to execute
1303 the following lines before doing anything else, just to keep people
1306 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1307 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1308 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};