3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTuU> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
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> ]...>
20 Upon startup, Perl looks for your script in one of the following
27 Specified line by line via B<-e> switches on the command line.
31 Contained in the file specified by the first filename on the command line.
32 (Note that systems supporting the #! notation invoke interpreters this way.)
36 Passed in implicitly via standard input. This works only if there are
37 no filename arguments--to pass arguments to a STDIN script you
38 must explicitly specify a "-" for the script name.
42 With methods 2 and 3, Perl starts parsing the input file from the
43 beginning, unless you've specified a B<-x> switch, in which case it
44 scans for the first line starting with #! and containing the word
45 "perl", and starts there instead. This is useful for running a script
46 embedded in a larger message. (In this case you would indicate the end
47 of the script using the __END__ token.)
49 The #! line is always examined for switches as the line is being
50 parsed. Thus, if you're on a machine that allows only one argument
51 with the #! line, or worse, doesn't even recognize the #! line, you
52 still can get consistent switch behavior regardless of how Perl was
53 invoked, even if B<-x> was used to find the beginning of the script.
55 Because many operating systems silently chop off kernel interpretation of
56 the #! line after 32 characters, some switches may be passed in on the
57 command line, and some may not; you could even get a "-" without its
58 letter, if you're not careful. You probably want to make sure that all
59 your switches fall either before or after that 32 character boundary.
60 Most switches don't actually care if they're processed redundantly, but
61 getting a - instead of a complete switch could cause Perl to try to
62 execute standard input instead of your script. And a partial B<-I> switch
63 could also cause odd results.
65 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
66 The sequences "-*" and "- " are specifically ignored so that you could,
67 if you were so inclined, say
69 #!/bin/sh -- # -*- perl -*- -p
70 eval 'exec /usr/bin/perl $0 -S ${1+"$@"}'
71 if $running_under_some_shell;
73 to let Perl see the B<-p> switch.
75 If the #! line does not contain the word "perl", the program named after
76 the #! is executed instead of the Perl interpreter. This is slightly
77 bizarre, but it helps people on machines that don't do #!, because they
78 can tell a program that their SHELL is /usr/bin/perl, and Perl will then
79 dispatch the program to the correct interpreter for them.
81 After locating your script, Perl compiles the entire script to an
82 internal form. If there are any compilation errors, execution of the
83 script is not attempted. (This is unlike the typical shell script,
84 which might run partway through before finding a syntax error.)
86 If the script is syntactically correct, it is executed. If the script
87 runs off the end without hitting an exit() or die() operator, an implicit
88 C<exit(0)> is provided to indicate successful completion.
90 =head2 #! and quoting on non-Unix systems
92 Unix's #! technique can be simulated on other systems:
100 extproc perl -S -your_switches
102 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
107 Create a batch file to run your script, and codify it in
108 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
109 distribution for more information).
113 The Win95/NT installation, when using the Activeware port of Perl,
114 will modify the Registry to associate the .pl extension with the perl
115 interpreter. If you install another port, or (eventually) build your
116 own Win95/NT Perl using WinGCC, then you'll have to modify the
121 Macintosh perl scripts will have the the appropriate Creator and
122 Type, so that double-clicking them will invoke the perl application.
126 Command-interpreters on non-Unix systems have rather different ideas
127 on quoting than Unix shells. You'll need to learn the special
128 characters in your command-interpreter (C<*>, C<\> and C<"> are
129 common) and how to protect whitespace and these characters to run
130 one-liners (see C<-e> below).
132 On some systems, you may have to change single-quotes to double ones,
133 which you must I<NOT> do on Unix or Plan9 systems. You might also
134 have to change a single % to a %%.
139 perl -e 'print "Hello world\n"'
142 perl -e "print \"Hello world\n\""
145 print "Hello world\n"
146 (then Run "Myscript" or Shift-Command-R)
149 perl -e "print ""Hello world\n"""
151 The problem is that none of this is reliable: it depends on the command
152 tirely possible neither works. If 4DOS was the command shell, I'd
153 probably have better luck like this:
155 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
157 CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
158 when nobody was looking, but just try to find documentation for its
161 Under the Mac, it depends which environment you are using. The MacPerl
162 shell, or MPW, is much like Unix shells in its support for several
163 quoting variants, except that it makes free use of the Mac's non-ASCII
164 characters as control characters.
166 I'm afraid that there is no general solution to all of this. It is a
167 mess, pure and simple.
169 [Some of this answer was contributed by Kenneth Albanowski.]
173 A single-character switch may be combined with the following switch, if
176 #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
182 =item B<-0>[I<digits>]
184 specifies the input record separator (C<$/>) as an octal number. If there are
185 no digits, the null character is the separator. Other switches may
186 precede or follow the digits. For example, if you have a version of
187 B<find> which can print filenames terminated by the null character, you
190 find . -name '*.bak' -print0 | perl -n0e unlink
192 The special value 00 will cause Perl to slurp files in paragraph mode.
193 The value 0777 will cause Perl to slurp files whole because there is no
194 legal character with that value.
198 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
199 split command to the @F array is done as the first thing inside the
200 implicit while loop produced by the B<-n> or B<-p>.
202 perl -ane 'print pop(@F), "\n";'
211 An alternate delimiter may be specified using B<-F>.
215 causes Perl to check the syntax of the script and then exit without
216 executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
217 because these are considered as occurring outside the execution of
222 runs the script under the Perl debugger. See L<perldebug>.
226 runs the script under the control of a debugging or tracing module
227 installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
228 Devel::DProf profiler. See L<perldebug>.
234 sets debugging flags. To watch how it executes your script, use
235 B<-D14>. (This works only if debugging is compiled into your
236 Perl.) Another nice value is B<-D1024>, which lists your compiled
237 syntax tree. And B<-D512> displays compiled regular expressions. As an
238 alternative specify a list of letters instead of numbers (e.g., B<-D14> is
239 equivalent to B<-Dtls>):
241 1 p Tokenizing and Parsing
243 4 l Label Stack Processing
245 16 o Operator Node Construction
246 32 c String/Numeric Conversions
247 64 P Print Preprocessor Command for -P
248 128 m Memory Allocation
249 256 f Format Processing
250 512 r Regular Expression Parsing
251 1024 x Syntax Tree Dump
252 2048 u Tainting Checks
253 4096 L Memory Leaks (not supported anymore)
254 8192 H Hash Dump -- usurps values()
255 16384 X Scratchpad Allocation
258 =item B<-e> I<commandline>
260 may be used to enter one line of script.
261 If B<-e> is given, Perl
262 will not look for a script filename in the argument list.
263 Multiple B<-e> commands may
264 be given to build up a multi-line script.
265 Make sure to use semicolons where you would in a normal program.
267 =item B<-F>I<pattern>
269 specifies the pattern to split on if B<-a> is also in effect. The
270 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
271 put in single quotes.
275 prints a summary of the options.
277 =item B<-i>[I<extension>]
279 specifies that files processed by the C<E<lt>E<gt>> construct are to be edited
280 in-place. It does this by renaming the input file, opening the output
281 file by the original name, and selecting that output file as the default
282 for print() statements. The extension, if supplied, is added to the name
283 of the old file to make a backup copy. If no extension is supplied, no
284 backup is made. From the shell, saying
286 $ perl -p -i.bak -e "s/foo/bar/; ... "
288 is the same as using the script:
290 #!/usr/bin/perl -pi.bak
293 which is equivalent to
297 if ($ARGV ne $oldargv) {
298 rename($ARGV, $ARGV . '.bak');
299 open(ARGVOUT, ">$ARGV");
306 print; # this prints to original filename
310 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
311 know when the filename has changed. It does, however, use ARGVOUT for
312 the selected filehandle. Note that STDOUT is restored as the
313 default output filehandle after the loop.
315 You can use C<eof> without parenthesis to locate the end of each input file,
316 in case you want to append to each file, or reset line numbering (see
317 example in L<perlfunc/eof>).
319 =item B<-I>I<directory>
321 Directories specified by B<-I> are prepended to the search path for
322 modules (C<@INC>), and also tells the C preprocessor where to search for
323 include files. The C preprocessor is invoked with B<-P>; by default it
324 searches /usr/include and /usr/lib/perl.
326 =item B<-l>[I<octnum>]
328 enables automatic line-ending processing. It has two effects: first,
329 it automatically chomps "C<$/>" (the input record separator) when used
330 with B<-n> or B<-p>, and second, it assigns "C<$\>"
331 (the output record separator) to have the value of I<octnum> so that
332 any print statements will have that separator added back on. If
333 I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
334 instance, to trim lines to 80 columns:
336 perl -lpe 'substr($_, 80) = ""'
338 Note that the assignment C<$\ = $/> is done when the switch is processed,
339 so the input record separator can be different than the output record
340 separator if the B<-l> switch is followed by a B<-0> switch:
342 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
344 This sets C<$\> to newline and then sets C<$/> to the null character.
346 =item B<-m>[B<->]I<module>
348 =item B<-M>[B<->]I<module>
350 =item B<-M>[B<->]I<'module ...'>
352 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
354 C<-m>I<module> executes C<use> I<module> C<();> before executing your
357 C<-M>I<module> executes C<use> I<module> C<;> before executing your
358 script. You can use quotes to add extra code after the module name,
359 e.g., C<-M'module qw(foo bar)'>.
361 If the first character after the C<-M> or C<-m> is a dash (C<->)
362 then the 'use' is replaced with 'no'.
364 A little built-in syntactic sugar means you can also say
365 C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for
366 C<-M'module qw(foo bar)'>. This avoids the need to use quotes when
367 importing symbols. The actual code generated by C<-Mmodule=foo,bar> is
368 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
369 removes the distinction between C<-m> and C<-M>.
373 causes Perl to assume the following loop around your script, which
374 makes it iterate over filename arguments somewhat like B<sed -n> or
378 ... # your script goes here
381 Note that the lines are not printed by default. See B<-p> to have
382 lines printed. Here is an efficient way to delete all files older than
385 find . -mtime +7 -print | perl -nle 'unlink;'
387 This is faster than using the C<-exec> switch of B<find> because you don't
388 have to start a process on every filename found.
390 C<BEGIN> and C<END> blocks may be used to capture control before or after
391 the implicit loop, just as in B<awk>.
395 causes Perl to assume the following loop around your script, which
396 makes it iterate over filename arguments somewhat like B<sed>:
400 ... # your script goes here
405 Note that the lines are printed automatically. To suppress printing
406 use the B<-n> switch. A B<-p> overrides a B<-n> switch.
408 C<BEGIN> and C<END> blocks may be used to capture control before or after
409 the implicit loop, just as in awk.
413 causes your script to be run through the C preprocessor before
414 compilation by Perl. (Because both comments and cpp directives begin
415 with the # character, you should avoid starting comments with any words
416 recognized by the C preprocessor such as "if", "else", or "define".)
420 enables some rudimentary switch parsing for switches on the command
421 line after the script name but before any filename arguments (or before
422 a B<-->). Any switch found there is removed from @ARGV and sets the
423 corresponding variable in the Perl script. The following script
424 prints "true" if and only if the script is invoked with a B<-xyz> switch.
427 if ($xyz) { print "true\n"; }
431 makes Perl use the PATH environment variable to search for the
432 script (unless the name of the script starts with a slash). Typically
433 this is used to emulate #! startup on machines that don't support #!,
434 in the following manner:
437 eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
438 if $running_under_some_shell;
440 The system ignores the first line and feeds the script to /bin/sh,
441 which proceeds to try to execute the Perl script as a shell script.
442 The shell executes the second line as a normal shell command, and thus
443 starts up the Perl interpreter. On some systems $0 doesn't always
444 contain the full pathname, so the B<-S> tells Perl to search for the
445 script if necessary. After Perl locates the script, it parses the
446 lines and ignores them because the variable $running_under_some_shell
447 is never true. A better construct than C<$*> would be C<${1+"$@"}>, which
448 handles embedded spaces and such in the filenames, but doesn't work if
449 the script is being interpreted by csh. To start up sh rather
450 than csh, some systems may have to replace the #! line with a line
451 containing just a colon, which will be politely ignored by Perl. Other
452 systems can't control that, and need a totally devious construct that
453 will work under any of csh, sh, or Perl, such as the following:
455 eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
456 & eval 'exec /usr/bin/perl -S $0 $argv:q'
457 if $running_under_some_shell;
461 forces "taint" checks to be turned on so you can test them. Ordinarily these checks are
462 done only when running setuid or setgid. It's a good idea to turn
463 them on explicitly for programs run on another's behalf, such as CGI
464 programs. See L<perlsec>.
468 causes Perl to dump core after compiling your script. You can then
469 take this core dump and turn it into an executable file by using the
470 B<undump> program (not supplied). This speeds startup at the expense of
471 some disk space (which you can minimize by stripping the executable).
472 (Still, a "hello world" executable comes out to about 200K on my
473 machine.) If you want to execute a portion of your script before dumping,
474 use the dump() operator instead. Note: availability of B<undump> is
475 platform specific and may not be available for a specific port of
480 allows Perl to do unsafe operations. Currently the only "unsafe"
481 operations are the unlinking of directories while running as superuser,
482 and running setuid programs with fatal taint checks turned into
487 prints the version and patchlevel of your Perl executable.
491 prints summary of the major perl configuration values and the current
496 Prints to STDOUT the value of the named configuration variable.
500 prints warnings about variable names that are mentioned only once, and
501 scalar variables that are used before being set. Also warns about
502 redefined subroutines, and references to undefined filehandles or
503 filehandles opened read-only that you are attempting to write on. Also
504 warns you if you use values as a number that doesn't look like numbers,
505 using an array as though it were a scalar, if your subroutines recurse
506 more than 100 deep, and innumerable other things.
508 You can disable specific warnings using C<__WARN__> hooks, as described
509 in L<perlvar> and L<perlfunc/warn>. See also L<perldiag> and L<perltrap>.
511 =item B<-x> I<directory>
513 tells Perl that the script is embedded in a message. Leading
514 garbage will be discarded until the first line that starts with #! and
515 contains the string "perl". Any meaningful switches on that line will
516 be applied. If a directory name is specified, Perl will switch to
517 that directory before running the script. The B<-x> switch controls
518 only the disposal of leading garbage. The script must be
519 terminated with C<__END__> if there is trailing garbage to be ignored (the
520 script can process any or all of the trailing garbage via the DATA
521 filehandle if desired).
531 Used if chdir has no argument.
535 Used if chdir has no argument and HOME is not set.
539 Used in executing subprocesses, and in finding the script if B<-S> is
544 A colon-separated list of directories in which to look for Perl library
545 files before looking in the standard library and the current
546 directory. If PERL5LIB is not defined, PERLLIB is used. When running
547 taint checks (because the script was running setuid or setgid, or the
548 B<-T> switch was used), neither variable is used. The script should
551 use lib "/my/directory";
555 A colon-separated list of directories in which to look for Perl library
556 files before looking in the standard library and the current directory.
557 If PERL5LIB is defined, PERLLIB is not used.
561 The command used to load the debugger code. The default is:
563 BEGIN { require 'perl5db.pl' }
565 =item PERL_DEBUG_MSTATS
567 Relevant only if your perl executable was built with B<-DDEBUGGING_MSTATS>,
568 if set, this causes memory statistics to be dumped after execution. If set
569 to an integer greater than one, also causes memory statistics to be dumped
572 =item PERL_DESTRUCT_LEVEL
574 Relevant only if your perl executable was built with B<-DDEBUGGING>,
575 this controls the behavior of global destruction of objects and other
580 Perl also has environment variables that control how Perl handles data
581 specific to particular natural languages. See L<perllocale>.
583 Apart from these, Perl uses no other environment variables, except
584 to make them available to the script being executed, and to child
585 processes. However, scripts running setuid would do well to execute
586 the following lines before doing anything else, just to keep people
589 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
590 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
591 $ENV{'IFS'} = '' if defined $ENV{'IFS'};