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 As of Perl 5, the #! line is always examined for switches as the line is
50 being 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 still
52 can get consistent switch behavior regardless of how Perl was invoked,
53 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 perl $0 -S ${1+"$@"}'
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.
92 A single-character switch may be combined with the following switch, if
95 #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
101 =item B<-0>[I<digits>]
103 specifies the input record separator (C<$/>) as an octal number. If there are
104 no digits, the null character is the separator. Other switches may
105 precede or follow the digits. For example, if you have a version of
106 B<find> which can print filenames terminated by the null character, you
109 find . -name '*.bak' -print0 | perl -n0e unlink
111 The special value 00 will cause Perl to slurp files in paragraph mode.
112 The value 0777 will cause Perl to slurp files whole because there is no
113 legal character with that value.
117 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
118 split command to the @F array is done as the first thing inside the
119 implicit while loop produced by the B<-n> or B<-p>.
121 perl -ane 'print pop(@F), "\n";'
130 An alternate delimiter may be specified using B<-F>.
134 causes Perl to check the syntax of the script and then exit without
135 executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
136 because these are considered as occurring outside the execution of
141 runs the script under the Perl debugger. See L<perldebug>.
145 runs the script under the control of a debugging or tracing module
146 installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
147 Devel::DProf profiler. See L<perldebug>.
153 sets debugging flags. To watch how it executes your script, use
154 B<-D14>. (This works only if debugging is compiled into your
155 Perl.) Another nice value is B<-D1024>, which lists your compiled
156 syntax tree. And B<-D512> displays compiled regular expressions. As an
157 alternative specify a list of letters instead of numbers (e.g., B<-D14> is
158 equivalent to B<-Dtls>):
160 1 p Tokenizing and Parsing
162 4 l Label Stack Processing
164 16 o Operator Node Construction
165 32 c String/Numeric Conversions
166 64 P Print Preprocessor Command for -P
167 128 m Memory Allocation
168 256 f Format Processing
169 512 r Regular Expression Parsing
170 1024 x Syntax Tree Dump
171 2048 u Tainting Checks
172 4096 L Memory Leaks (not supported anymore)
173 8192 H Hash Dump -- usurps values()
174 16384 X Scratchpad Allocation
177 =item B<-e> I<commandline>
179 may be used to enter one line of script.
180 If B<-e> is given, Perl
181 will not look for a script filename in the argument list.
182 Multiple B<-e> commands may
183 be given to build up a multi-line script.
184 Make sure to use semicolons where you would in a normal program.
186 =item B<-F>I<pattern>
188 specifies the pattern to split on if B<-a> is also in effect. The
189 pattern may be surrounded by C<//>, C<""> or C<''>, otherwise it will be
190 put in single quotes.
194 prints a summary of the options.
196 =item B<-i>[I<extension>]
198 specifies that files processed by the C<E<lt>E<gt>> construct are to be edited
199 in-place. It does this by renaming the input file, opening the output
200 file by the original name, and selecting that output file as the default
201 for print() statements. The extension, if supplied, is added to the name
202 of the old file to make a backup copy. If no extension is supplied, no
203 backup is made. From the shell, saying
205 $ perl -p -i.bak -e "s/foo/bar/; ... "
207 is the same as using the script:
209 #!/usr/bin/perl -pi.bak
212 which is equivalent to
216 if ($ARGV ne $oldargv) {
217 rename($ARGV, $ARGV . '.bak');
218 open(ARGVOUT, ">$ARGV");
225 print; # this prints to original filename
229 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
230 know when the filename has changed. It does, however, use ARGVOUT for
231 the selected filehandle. Note that STDOUT is restored as the
232 default output filehandle after the loop.
234 You can use C<eof> without parenthesis to locate the end of each input file,
235 in case you want to append to each file, or reset line numbering (see
236 example in L<perlfunc/eof>).
238 =item B<-I>I<directory>
240 Directories specified by B<-I> are prepended to the search path for
241 modules (C<@INC>), and also tells the C preprocessor where to search for
242 include files. The C preprocessor is invoked with B<-P>; by default it
243 searches /usr/include and /usr/lib/perl.
245 =item B<-l>[I<octnum>]
247 enables automatic line-ending processing. It has two effects: first,
248 it automatically chomps "C<$/>" (the input record separator) when used
249 with B<-n> or B<-p>, and second, it assigns "C<$\>"
250 (the output record separator) to have the value of I<octnum> so that
251 any print statements will have that separator added back on. If
252 I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
253 instance, to trim lines to 80 columns:
255 perl -lpe 'substr($_, 80) = ""'
257 Note that the assignment C<$\ = $/> is done when the switch is processed,
258 so the input record separator can be different than the output record
259 separator if the B<-l> switch is followed by a B<-0> switch:
261 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
263 This sets C<$\> to newline and then sets C<$/> to the null character.
265 =item B<-m>[B<->]I<module>
267 =item B<-M>[B<->]I<module>
269 =item B<-M>[B<->]I<'module ...'>
271 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
273 C<-m>I<module> executes C<use> I<module> C<();> before executing your
276 C<-M>I<module> executes C<use> I<module> C<;> before executing your
277 script. You can use quotes to add extra code after the module name,
278 e.g., C<-M'module qw(foo bar)'>.
280 If the first character after the C<-M> or C<-m> is a dash (C<->)
281 then the 'use' is replaced with 'no'.
283 A little built-in syntactic sugar means you can also say
284 C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for
285 C<-M'module qw(foo bar)'>. This avoids the need to use quotes when
286 importing symbols. The actual code generated by C<-Mmodule=foo,bar> is
287 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
288 removes the distinction between C<-m> and C<-M>.
292 causes Perl to assume the following loop around your script, which
293 makes it iterate over filename arguments somewhat like B<sed -n> or
297 ... # your script goes here
300 Note that the lines are not printed by default. See B<-p> to have
301 lines printed. Here is an efficient way to delete all files older than
304 find . -mtime +7 -print | perl -nle 'unlink;'
306 This is faster than using the C<-exec> switch of B<find> because you don't
307 have to start a process on every filename found.
309 C<BEGIN> and C<END> blocks may be used to capture control before or after
310 the implicit loop, just as in B<awk>.
314 causes Perl to assume the following loop around your script, which
315 makes it iterate over filename arguments somewhat like B<sed>:
319 ... # your script goes here
324 Note that the lines are printed automatically. To suppress printing
325 use the B<-n> switch. A B<-p> overrides a B<-n> switch.
327 C<BEGIN> and C<END> blocks may be used to capture control before or after
328 the implicit loop, just as in awk.
332 causes your script to be run through the C preprocessor before
333 compilation by Perl. (Because both comments and cpp directives begin
334 with the # character, you should avoid starting comments with any words
335 recognized by the C preprocessor such as "if", "else" or "define".)
339 enables some rudimentary switch parsing for switches on the command
340 line after the script name but before any filename arguments (or before
341 a B<-->). Any switch found there is removed from @ARGV and sets the
342 corresponding variable in the Perl script. The following script
343 prints "true" if and only if the script is invoked with a B<-xyz> switch.
346 if ($xyz) { print "true\n"; }
350 makes Perl use the PATH environment variable to search for the
351 script (unless the name of the script starts with a slash). Typically
352 this is used to emulate #! startup on machines that don't support #!,
353 in the following manner:
356 eval "exec /usr/bin/perl -S $0 $*"
357 if $running_under_some_shell;
359 The system ignores the first line and feeds the script to /bin/sh,
360 which proceeds to try to execute the Perl script as a shell script.
361 The shell executes the second line as a normal shell command, and thus
362 starts up the Perl interpreter. On some systems $0 doesn't always
363 contain the full pathname, so the B<-S> tells Perl to search for the
364 script if necessary. After Perl locates the script, it parses the
365 lines and ignores them because the variable $running_under_some_shell
366 is never true. A better construct than C<$*> would be C<${1+"$@"}>, which
367 handles embedded spaces and such in the filenames, but doesn't work if
368 the script is being interpreted by csh. To start up sh rather
369 than csh, some systems may have to replace the #! line with a line
370 containing just a colon, which will be politely ignored by Perl. Other
371 systems can't control that, and need a totally devious construct that
372 will work under any of csh, sh or Perl, such as the following:
374 eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
375 & eval 'exec /usr/bin/perl -S $0 $argv:q'
380 forces "taint" checks to be turned on so you can test them. Ordinarily these checks are
381 done only when running setuid or setgid. It's a good idea to turn
382 them on explicitly for programs run on another's behalf, such as CGI
383 programs. See L<perlsec>.
387 causes Perl to dump core after compiling your script. You can then
388 take this core dump and turn it into an executable file by using the
389 B<undump> program (not supplied). This speeds startup at the expense of
390 some disk space (which you can minimize by stripping the executable).
391 (Still, a "hello world" executable comes out to about 200K on my
392 machine.) If you want to execute a portion of your script before dumping,
393 use the dump() operator instead. Note: availability of B<undump> is
394 platform specific and may not be available for a specific port of
399 allows Perl to do unsafe operations. Currently the only "unsafe"
400 operations are the unlinking of directories while running as superuser,
401 and running setuid programs with fatal taint checks turned into
406 prints the version and patchlevel of your Perl executable.
410 prints summary of the major perl configuration values and the current
415 Prints to STDOUT the value of the named configuration variable.
419 prints warnings about variable names that are mentioned only once, and
420 scalar variables that are used before being set. Also warns about
421 redefined subroutines, and references to undefined filehandles or
422 filehandles opened read-only that you are attempting to write on. Also
423 warns you if you use values as a number that doesn't look like numbers, using
424 an array as though it were a scalar, if
425 your subroutines recurse more than 100 deep, and innumerable other things.
426 See L<perldiag> and L<perltrap>.
428 =item B<-x> I<directory>
430 tells Perl that the script is embedded in a message. Leading
431 garbage will be discarded until the first line that starts with #! and
432 contains the string "perl". Any meaningful switches on that line will
433 be applied (but only one group of switches, as with normal #!
434 processing). If a directory name is specified, Perl will switch to
435 that directory before running the script. The B<-x> switch controls
436 only the disposal of leading garbage. The script must be
437 terminated with C<__END__> if there is trailing garbage to be ignored (the
438 script can process any or all of the trailing garbage via the DATA
439 filehandle if desired).