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1 | =head1 NAME |
2 | ||
3 | perlrun - how to execute the Perl interpreter | |
4 | ||
5 | =head1 SYNOPSIS | |
6 | ||
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>] >]> | |
13 | S<[ B<-P> ]> | |
14 | S<[ B<-S> ]> | |
15 | S<[ B<-x>[I<dir>] ]> | |
16 | S<[ B<-i>[I<extension>] ]> | |
17 | S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...> | |
18 | ||
19 | =head1 DESCRIPTION | |
20 | ||
21 | The normal way to run a Perl program is by making it directly | |
22 | executable, or else by passing the name of the source file as an | |
23 | argument on the command line. (An interactive Perl environment | |
24 | is also possible--see L<perldebug> for details on how to do that.) | |
25 | Upon startup, Perl looks for your program in one of the following | |
26 | places: | |
27 | ||
28 | =over 4 | |
29 | ||
30 | =item 1. | |
31 | ||
32 | Specified line by line via B<-e> switches on the command line. | |
33 | ||
34 | =item 2. | |
35 | ||
36 | Contained in the file specified by the first filename on the command line. | |
37 | (Note that systems supporting the #! notation invoke interpreters this | |
38 | way. See L<Location of Perl>.) | |
39 | ||
40 | =item 3. | |
41 | ||
42 | Passed in implicitly via standard input. This works only if there are | |
43 | no filename arguments--to pass arguments to a STDIN-read program you | |
44 | must explicitly specify a "-" for the program name. | |
45 | ||
46 | =back | |
47 | ||
48 | With methods 2 and 3, Perl starts parsing the input file from the | |
49 | beginning, unless you've specified a B<-x> switch, in which case it | |
50 | scans for the first line starting with #! and containing the word | |
51 | "perl", and starts there instead. This is useful for running a program | |
52 | embedded in a larger message. (In this case you would indicate the end | |
53 | of the program using the C<__END__> token.) | |
54 | ||
55 | The #! line is always examined for switches as the line is being | |
56 | parsed. Thus, if you're on a machine that allows only one argument | |
57 | with the #! line, or worse, doesn't even recognize the #! line, you | |
58 | still can get consistent switch behavior regardless of how Perl was | |
59 | invoked, even if B<-x> was used to find the beginning of the program. | |
60 | ||
61 | Because historically some operating systems silently chopped off | |
62 | kernel interpretation of the #! line after 32 characters, some | |
63 | switches may be passed in on the command line, and some may not; | |
64 | you could even get a "-" without its letter, if you're not careful. | |
65 | You probably want to make sure that all your switches fall either | |
66 | before or after that 32-character boundary. Most switches don't | |
67 | actually care if they're processed redundantly, but getting a "-" | |
68 | instead of a complete switch could cause Perl to try to execute | |
69 | standard input instead of your program. And a partial B<-I> switch | |
70 | could also cause odd results. | |
71 | ||
72 | Some switches do care if they are processed twice, for instance | |
73 | combinations of B<-l> and B<-0>. Either put all the switches after | |
74 | the 32-character boundary (if applicable), or replace the use of | |
75 | B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>. | |
76 | ||
77 | Parsing of the #! switches starts wherever "perl" is mentioned in the line. | |
78 | The sequences "-*" and "- " are specifically ignored so that you could, | |
79 | if you were so inclined, say | |
80 | ||
81 | #!/bin/sh -- # -*- perl -*- -p | |
82 | eval 'exec perl -wS $0 ${1+"$@"}' | |
83 | if $running_under_some_shell; | |
84 | ||
85 | to let Perl see the B<-p> switch. | |
86 | ||
87 | A similar trick involves the B<env> program, if you have it. | |
88 | ||
89 | #!/usr/bin/env perl | |
90 | ||
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. | |
95 | ||
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. | |
101 | ||
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.) | |
106 | ||
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. | |
110 | ||
111 | =head2 #! and quoting on non-Unix systems | |
112 | X<hashbang> X<#!> | |
113 | ||
114 | Unix's #! technique can be simulated on other systems: | |
115 | ||
116 | =over 4 | |
117 | ||
118 | =item OS/2 | |
119 | ||
120 | Put | |
121 | ||
122 | extproc perl -S -your_switches | |
123 | ||
124 | as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's | |
125 | `extproc' handling). | |
126 | ||
127 | =item MS-DOS | |
128 | ||
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). | |
132 | ||
133 | =item Win95/NT | |
134 | ||
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. | |
141 | ||
142 | =item Macintosh | |
143 | ||
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/ . | |
148 | ||
149 | =item VMS | |
150 | ||
151 | Put | |
152 | ||
153 | $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' ! | |
154 | $ exit++ + ++$status != 0 and $exit = $status = undef; | |
155 | ||
156 | at the top of your program, where B<-mysw> are any command line switches you | |
157 | want to pass to Perl. You can now invoke the program directly, by saying | |
158 | C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly | |
159 | via F<DCL$PATH> by just using the name of the program). | |
160 | ||
161 | This incantation is a bit much to remember, but Perl will display it for | |
162 | you if you say C<perl "-V:startperl">. | |
163 | ||
164 | =back | |
165 | ||
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). | |
171 | ||
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 %%. | |
175 | ||
176 | For example: | |
177 | ||
178 | # Unix | |
179 | perl -e 'print "Hello world\n"' | |
180 | ||
181 | # MS-DOS, etc. | |
182 | perl -e "print \"Hello world\n\"" | |
183 | ||
184 | # Macintosh | |
185 | print "Hello world\n" | |
186 | (then Run "Myscript" or Shift-Command-R) | |
187 | ||
188 | # VMS | |
189 | perl -e "print ""Hello world\n""" | |
190 | ||
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: | |
194 | ||
195 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
196 | ||
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 | |
199 | quoting rules. | |
200 | ||
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. | |
205 | ||
206 | There is no general solution to all of this. It's just a mess. | |
207 | ||
208 | =head2 Location of Perl | |
209 | X<perl, location of interpreter> | |
210 | ||
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. | |
218 | ||
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. | |
222 | ||
223 | #!/usr/local/bin/perl5.00554 | |
224 | ||
225 | or if you just want to be running at least version, place a statement | |
226 | like this at the top of your program: | |
227 | ||
228 | use 5.005_54; | |
229 | ||
230 | =head2 Command Switches | |
231 | X<perl, command switches> X<command switches> | |
232 | ||
233 | As with all standard commands, a single-character switch may be | |
234 | clustered with the following switch, if any. | |
235 | ||
236 | #!/usr/bin/perl -spi.orig # same as -s -p -i.orig | |
237 | ||
238 | Switches include: | |
239 | ||
240 | =over 5 | |
241 | ||
242 | =item B<-0>[I<octal/hexadecimal>] | |
243 | X<-0> X<$/> | |
244 | ||
245 | specifies the input record separator (C<$/>) 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: | |
250 | ||
251 | find . -name '*.orig' -print0 | perl -n0e unlink | |
252 | ||
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. | |
256 | ||
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.) | |
261 | ||
262 | =item B<-a> | |
263 | X<-a> X<autosplit> | |
264 | ||
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>. | |
268 | ||
269 | perl -ane 'print pop(@F), "\n";' | |
270 | ||
271 | is equivalent to | |
272 | ||
273 | while (<>) { | |
274 | @F = split(' '); | |
275 | print pop(@F), "\n"; | |
276 | } | |
277 | ||
278 | An alternate delimiter may be specified using B<-F>. | |
279 | ||
280 | =item B<-C [I<number/list>]> | |
281 | X<-C> | |
282 | ||
283 | The C<-C> flag controls some Unicode of the Perl Unicode features. | |
284 | ||
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. | |
288 | ||
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 | |
292 | S 7 I + O + E | |
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 | |
295 | D 24 i + o | |
296 | A 32 the @ARGV elements are expected to be strings encoded in UTF-8 | |
297 | L 64 normally the "IOEioA" are unconditional, | |
298 | the L makes them conditional on the locale environment | |
299 | variables (the LC_ALL, LC_TYPE, and LANG, in the order | |
300 | of decreasing precedence) -- if the variables indicate | |
301 | UTF-8, then the selected "IOEioA" are in effect | |
302 | ||
303 | For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both | |
304 | STDOUT and STDERR. Repeating letters is just redundant, not cumulative | |
305 | nor toggling. | |
306 | ||
307 | The C<io> options mean that any subsequent open() (or similar I/O | |
308 | operations) will have the C<:utf8> PerlIO layer implicitly applied | |
309 | to them, in other words, UTF-8 is expected from any input stream, | |
310 | and UTF-8 is produced to any output stream. This is just the default, | |
311 | with explicit layers in open() and with binmode() one can manipulate | |
312 | streams as usual. | |
313 | ||
314 | C<-C> on its own (not followed by any number or option list), or the | |
315 | empty string C<""> for the C<PERL_UNICODE> environment variable, has the | |
316 | same effect as C<-CSDL>. In other words, the standard I/O handles and | |
317 | the default C<open()> layer are UTF-8-fied B<but> only if the locale | |
318 | environment variables indicate a UTF-8 locale. This behaviour follows | |
319 | the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0. | |
320 | ||
321 | You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly | |
322 | disable all the above Unicode features. | |
323 | ||
324 | The read-only magic variable C<${^UNICODE}> reflects the numeric value | |
325 | of this setting. This is variable is set during Perl startup and is | |
326 | thereafter read-only. If you want runtime effects, use the three-arg | |
327 | open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>), | |
328 | and the C<open> pragma (see L<open>). | |
329 | ||
330 | (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch | |
331 | that enabled the use of Unicode-aware "wide system call" Win32 APIs. | |
332 | This feature was practically unused, however, and the command line | |
333 | switch was therefore "recycled".) | |
334 | ||
335 | =item B<-c> | |
336 | X<-c> | |
337 | ||
338 | causes Perl to check the syntax of the program and then exit without | |
339 | executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and | |
340 | C<use> blocks, because these are considered as occurring outside the | |
341 | execution of your program. C<INIT> and C<END> blocks, however, will | |
342 | be skipped. | |
343 | ||
344 | =item B<-d> | |
345 | X<-d> X<-dt> | |
346 | ||
347 | =item B<-dt> | |
348 | ||
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. | |
352 | ||
353 | =item B<-d:>I<foo[=bar,baz]> | |
354 | X<-d> X<-dt> | |
355 | ||
356 | =item B<-dt:>I<foo[=bar,baz]> | |
357 | ||
358 | runs the program under the control of a debugging, profiling, or | |
359 | tracing module installed as Devel::foo. E.g., B<-d:DProf> executes | |
360 | the program using the Devel::DProf profiler. As with the B<-M> | |
361 | flag, options may be passed to the Devel::foo package where they | |
362 | will be received and interpreted by the Devel::foo::import routine. | |
363 | The comma-separated list of options must follow a C<=> character. | |
364 | If B<t> is specified, it indicates to the debugger that threads | |
365 | will be used in the code being debugged. | |
366 | See L<perldebug>. | |
367 | ||
368 | =item B<-D>I<letters> | |
369 | X<-D> X<DEBUGGING> X<-DDEBUGGING> | |
370 | ||
371 | =item B<-D>I<number> | |
372 | ||
373 | sets debugging flags. To watch how it executes your program, use | |
374 | B<-Dtls>. (This works only if debugging is compiled into your | |
375 | Perl.) Another nice value is B<-Dx>, which lists your compiled | |
376 | syntax tree. And B<-Dr> displays compiled regular expressions; | |
377 | the format of the output is explained in L<perldebguts>. | |
378 | ||
379 | As an alternative, specify a number instead of list of letters (e.g., | |
380 | B<-D14> is equivalent to B<-Dtls>): | |
381 | ||
382 | 1 p Tokenizing and parsing | |
383 | 2 s Stack snapshots (with v, displays all stacks) | |
384 | 4 l Context (loop) stack processing | |
385 | 8 t Trace execution | |
386 | 16 o Method and overloading resolution | |
387 | 32 c String/numeric conversions | |
388 | 64 P Print profiling info, preprocessor command for -P, source file input state | |
389 | 128 m Memory allocation | |
390 | 256 f Format processing | |
391 | 512 r Regular expression parsing and execution | |
392 | 1024 x Syntax tree dump | |
393 | 2048 u Tainting checks | |
394 | 4096 (Obsolete, previously used for LEAKTEST) | |
395 | 8192 H Hash dump -- usurps values() | |
396 | 16384 X Scratchpad allocation | |
397 | 32768 D Cleaning up | |
398 | 65536 S Thread synchronization | |
399 | 131072 T Tokenising | |
400 | 262144 R Include reference counts of dumped variables (eg when using -Ds) | |
401 | 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB | |
402 | 1048576 v Verbose: use in conjunction with other flags | |
403 | 8388608 q quiet - currently only suppresses the "EXECUTING" message | |
404 | ||
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. | |
410 | ||
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 | |
414 | ||
415 | # If you have "env" utility | |
416 | env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program | |
417 | ||
418 | # Bourne shell syntax | |
419 | $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program | |
420 | ||
421 | # csh syntax | |
422 | % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program) | |
423 | ||
424 | See L<perldebug> for details and variations. | |
425 | ||
426 | =item B<-e> I<commandline> | |
427 | X<-e> | |
428 | ||
429 | may be used to enter one line of program. If B<-e> is given, Perl | |
430 | will not look for a filename in the argument list. Multiple B<-e> | |
431 | commands may be given to build up a multi-line script. Make sure | |
432 | to use semicolons where you would in a normal program. | |
433 | ||
434 | =item B<-f> | |
435 | X<-f> | |
436 | ||
437 | Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup. | |
438 | ||
439 | Perl can be built so that it by default will try to execute | |
440 | F<$Config{sitelib}/sitecustomize.pl> at startup. This is a hook that | |
441 | allows the sysadmin to customize how perl behaves. It can for | |
442 | instance be used to add entries to the @INC array to make perl find | |
443 | modules in non-standard locations. | |
444 | ||
445 | =item B<-F>I<pattern> | |
446 | X<-F> | |
447 | ||
448 | specifies the pattern to split on if B<-a> is also in effect. The | |
449 | pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be | |
450 | put in single quotes. You can't use literal whitespace in the pattern. | |
451 | ||
452 | =item B<-h> | |
453 | X<-h> | |
454 | ||
455 | prints a summary of the options. | |
456 | ||
457 | =item B<-i>[I<extension>] | |
458 | X<-i> X<in-place> | |
459 | ||
460 | specifies that files processed by the C<E<lt>E<gt>> construct are to be | |
461 | edited in-place. It does this by renaming the input file, opening the | |
462 | output file by the original name, and selecting that output file as the | |
463 | default for print() statements. The extension, if supplied, is used to | |
464 | modify the name of the old file to make a backup copy, following these | |
465 | rules: | |
466 | ||
467 | If no extension is supplied, no backup is made and the current file is | |
468 | overwritten. | |
469 | ||
470 | If the extension doesn't contain a C<*>, then it is appended to the | |
471 | end of the current filename as a suffix. If the extension does | |
472 | contain one or more C<*> characters, then each C<*> is replaced | |
473 | with the current filename. In Perl terms, you could think of this | |
474 | as: | |
475 | ||
476 | ($backup = $extension) =~ s/\*/$file_name/g; | |
477 | ||
478 | This allows you to add a prefix to the backup file, instead of (or in | |
479 | addition to) a suffix: | |
480 | ||
481 | $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA' | |
482 | ||
483 | Or even to place backup copies of the original files into another | |
484 | directory (provided the directory already exists): | |
485 | ||
486 | $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig' | |
487 | ||
488 | These sets of one-liners are equivalent: | |
489 | ||
490 | $ perl -pi -e 's/bar/baz/' fileA # overwrite current file | |
491 | $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file | |
492 | ||
493 | $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' | |
494 | $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' | |
495 | ||
496 | From the shell, saying | |
497 | ||
498 | $ perl -p -i.orig -e "s/foo/bar/; ... " | |
499 | ||
500 | is the same as using the program: | |
501 | ||
502 | #!/usr/bin/perl -pi.orig | |
503 | s/foo/bar/; | |
504 | ||
505 | which is equivalent to | |
506 | ||
507 | #!/usr/bin/perl | |
508 | $extension = '.orig'; | |
509 | LINE: while (<>) { | |
510 | if ($ARGV ne $oldargv) { | |
511 | if ($extension !~ /\*/) { | |
512 | $backup = $ARGV . $extension; | |
513 | } | |
514 | else { | |
515 | ($backup = $extension) =~ s/\*/$ARGV/g; | |
516 | } | |
517 | rename($ARGV, $backup); | |
518 | open(ARGVOUT, ">$ARGV"); | |
519 | select(ARGVOUT); | |
520 | $oldargv = $ARGV; | |
521 | } | |
522 | s/foo/bar/; | |
523 | } | |
524 | continue { | |
525 | print; # this prints to original filename | |
526 | } | |
527 | select(STDOUT); | |
528 | ||
529 | except that the B<-i> form doesn't need to compare $ARGV to $oldargv to | |
530 | know when the filename has changed. It does, however, use ARGVOUT for | |
531 | the selected filehandle. Note that STDOUT is restored as the default | |
532 | output filehandle after the loop. | |
533 | ||
534 | As shown above, Perl creates the backup file whether or not any output | |
535 | is actually changed. So this is just a fancy way to copy files: | |
536 | ||
537 | $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3... | |
538 | or | |
539 | $ perl -p -i'.orig' -e 1 file1 file2 file3... | |
540 | ||
541 | You can use C<eof> without parentheses to locate the end of each input | |
542 | file, in case you want to append to each file, or reset line numbering | |
543 | (see example in L<perlfunc/eof>). | |
544 | ||
545 | If, for a given file, Perl is unable to create the backup file as | |
546 | specified in the extension then it will skip that file and continue on | |
547 | with the next one (if it exists). | |
548 | ||
549 | For a discussion of issues surrounding file permissions and B<-i>, | |
550 | 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?>. | |
551 | ||
552 | You cannot use B<-i> to create directories or to strip extensions from | |
553 | files. | |
554 | ||
555 | Perl does not expand C<~> in filenames, which is good, since some | |
556 | folks use it for their backup files: | |
557 | ||
558 | $ perl -pi~ -e 's/foo/bar/' file1 file2 file3... | |
559 | ||
560 | Note that because B<-i> renames or deletes the original file before | |
561 | creating a new file of the same name, UNIX-style soft and hard links will | |
562 | not be preserved. | |
563 | ||
564 | Finally, the B<-i> switch does not impede execution when no | |
565 | files are given on the command line. In this case, no backup is made | |
566 | (the original file cannot, of course, be determined) and processing | |
567 | proceeds from STDIN to STDOUT as might be expected. | |
568 | ||
569 | =item B<-I>I<directory> | |
570 | X<-I> X<@INC> | |
571 | ||
572 | Directories specified by B<-I> are prepended to the search path for | |
573 | modules (C<@INC>), and also tells the C preprocessor where to search for | |
574 | include files. The C preprocessor is invoked with B<-P>; by default it | |
575 | searches /usr/include and /usr/lib/perl. | |
576 | ||
577 | =item B<-l>[I<octnum>] | |
578 | X<-l> X<$/> X<$\> | |
579 | ||
580 | enables automatic line-ending processing. It has two separate | |
581 | effects. First, it automatically chomps C<$/> (the input record | |
582 | separator) when used with B<-n> or B<-p>. Second, it assigns C<$\> | |
583 | (the output record separator) to have the value of I<octnum> so | |
584 | that any print statements will have that separator added back on. | |
585 | If I<octnum> is omitted, sets C<$\> to the current value of | |
586 | C<$/>. For instance, to trim lines to 80 columns: | |
587 | ||
588 | perl -lpe 'substr($_, 80) = ""' | |
589 | ||
590 | Note that the assignment C<$\ = $/> is done when the switch is processed, | |
591 | so the input record separator can be different than the output record | |
592 | separator if the B<-l> switch is followed by a B<-0> switch: | |
593 | ||
594 | gnufind / -print0 | perl -ln0e 'print "found $_" if -p' | |
595 | ||
596 | This sets C<$\> to newline and then sets C<$/> to the null character. | |
597 | ||
598 | =item B<-m>[B<->]I<module> | |
599 | X<-m> X<-M> | |
600 | ||
601 | =item B<-M>[B<->]I<module> | |
602 | ||
603 | =item B<-M>[B<->]I<'module ...'> | |
604 | ||
605 | =item B<-[mM]>[B<->]I<module=arg[,arg]...> | |
606 | ||
607 | B<-m>I<module> executes C<use> I<module> C<();> before executing your | |
608 | program. | |
609 | ||
610 | B<-M>I<module> executes C<use> I<module> C<;> before executing your | |
611 | program. You can use quotes to add extra code after the module name, | |
612 | e.g., C<'-Mmodule qw(foo bar)'>. | |
613 | ||
614 | If the first character after the B<-M> or B<-m> is a dash (C<->) | |
615 | then the 'use' is replaced with 'no'. | |
616 | ||
617 | A little builtin syntactic sugar means you can also say | |
618 | B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for | |
619 | C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when | |
620 | importing symbols. The actual code generated by B<-Mmodule=foo,bar> is | |
621 | C<use module split(/,/,q{foo,bar})>. Note that the C<=> form | |
622 | removes the distinction between B<-m> and B<-M>. | |
623 | ||
624 | A consequence of this is that B<-MFoo=number> never does a version check | |
625 | (unless C<Foo::import()> itself is set up to do a version check, which | |
626 | could happen for example if Foo inherits from Exporter.) | |
627 | ||
628 | =item B<-n> | |
629 | X<-n> | |
630 | ||
631 | causes Perl to assume the following loop around your program, which | |
632 | makes it iterate over filename arguments somewhat like B<sed -n> or | |
633 | B<awk>: | |
634 | ||
635 | LINE: | |
636 | while (<>) { | |
637 | ... # your program goes here | |
638 | } | |
639 | ||
640 | Note that the lines are not printed by default. See B<-p> to have | |
641 | lines printed. If a file named by an argument cannot be opened for | |
642 | some reason, Perl warns you about it and moves on to the next file. | |
643 | ||
644 | Here is an efficient way to delete all files that haven't been modified for | |
645 | at least a week: | |
646 | ||
647 | find . -mtime +7 -print | perl -nle unlink | |
648 | ||
649 | This is faster than using the B<-exec> switch of B<find> because you don't | |
650 | have to start a process on every filename found. It does suffer from | |
651 | the bug of mishandling newlines in pathnames, which you can fix if | |
652 | you follow the example under B<-0>. | |
653 | ||
654 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
655 | the implicit program loop, just as in B<awk>. | |
656 | ||
657 | =item B<-p> | |
658 | X<-p> | |
659 | ||
660 | causes Perl to assume the following loop around your program, which | |
661 | makes it iterate over filename arguments somewhat like B<sed>: | |
662 | ||
663 | ||
664 | LINE: | |
665 | while (<>) { | |
666 | ... # your program goes here | |
667 | } continue { | |
668 | print or die "-p destination: $!\n"; | |
669 | } | |
670 | ||
671 | If a file named by an argument cannot be opened for some reason, Perl | |
672 | warns you about it, and moves on to the next file. Note that the | |
673 | lines are printed automatically. An error occurring during printing is | |
674 | treated as fatal. To suppress printing use the B<-n> switch. A B<-p> | |
675 | overrides a B<-n> switch. | |
676 | ||
677 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
678 | the implicit loop, just as in B<awk>. | |
679 | ||
680 | =item B<-P> | |
681 | X<-P> | |
682 | ||
683 | B<NOTE: Use of -P is strongly discouraged because of its inherent | |
684 | problems, including poor portability.> | |
685 | ||
686 | This option causes your program to be run through the C preprocessor before | |
687 | compilation by Perl. Because both comments and B<cpp> directives begin | |
688 | with the # character, you should avoid starting comments with any words | |
689 | recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">. | |
690 | ||
691 | If you're considering using C<-P>, you might also want to look at the | |
692 | Filter::cpp module from CPAN. | |
693 | ||
694 | The problems of -P include, but are not limited to: | |
695 | ||
696 | =over 10 | |
697 | ||
698 | =item * | |
699 | ||
700 | The C<#!> line is stripped, so any switches there don't apply. | |
701 | ||
702 | =item * | |
703 | ||
704 | A C<-P> on a C<#!> line doesn't work. | |
705 | ||
706 | =item * | |
707 | ||
708 | B<All> lines that begin with (whitespace and) a C<#> but | |
709 | do not look like cpp commands, are stripped, including anything | |
710 | inside Perl strings, regular expressions, and here-docs . | |
711 | ||
712 | =item * | |
713 | ||
714 | In some platforms the C preprocessor knows too much: it knows about | |
715 | the C++ -style until-end-of-line comments starting with C<"//">. | |
716 | This will cause problems with common Perl constructs like | |
717 | ||
718 | s/foo//; | |
719 | ||
720 | because after -P this will became illegal code | |
721 | ||
722 | s/foo | |
723 | ||
724 | The workaround is to use some other quoting separator than C<"/">, | |
725 | like for example C<"!">: | |
726 | ||
727 | s!foo!!; | |
728 | ||
729 | ||
730 | ||
731 | =item * | |
732 | ||
733 | It requires not only a working C preprocessor but also a working | |
734 | F<sed>. If not on UNIX, you are probably out of luck on this. | |
735 | ||
736 | =item * | |
737 | ||
738 | Script line numbers are not preserved. | |
739 | ||
740 | =item * | |
741 | ||
742 | The C<-x> does not work with C<-P>. | |
743 | ||
744 | =back | |
745 | ||
746 | =item B<-s> | |
747 | X<-s> | |
748 | ||
749 | enables rudimentary switch parsing for switches on the command | |
750 | line after the program name but before any filename arguments (or before | |
751 | an argument of B<-->). Any switch found there is removed from @ARGV and sets the | |
752 | corresponding variable in the Perl program. The following program | |
753 | prints "1" if the program is invoked with a B<-xyz> switch, and "abc" | |
754 | if it is invoked with B<-xyz=abc>. | |
755 | ||
756 | #!/usr/bin/perl -s | |
757 | if ($xyz) { print "$xyz\n" } | |
758 | ||
759 | Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant | |
760 | with C<strict refs>. Also, when using this option on a script with | |
761 | warnings enabled you may get a lot of spurious "used only once" warnings. | |
762 | ||
763 | =item B<-S> | |
764 | X<-S> | |
765 | ||
766 | makes Perl use the PATH environment variable to search for the | |
767 | program (unless the name of the program contains directory separators). | |
768 | ||
769 | On some platforms, this also makes Perl append suffixes to the | |
770 | filename while searching for it. For example, on Win32 platforms, | |
771 | the ".bat" and ".cmd" suffixes are appended if a lookup for the | |
772 | original name fails, and if the name does not already end in one | |
773 | of those suffixes. If your Perl was compiled with DEBUGGING turned | |
774 | on, using the -Dp switch to Perl shows how the search progresses. | |
775 | ||
776 | Typically this is used to emulate #! startup on platforms that don't | |
777 | support #!. Its also convenient when debugging a script that uses #!, | |
778 | and is thus normally found by the shell's $PATH search mechanism. | |
779 | ||
780 | This example works on many platforms that have a shell compatible with | |
781 | Bourne shell: | |
782 | ||
783 | #!/usr/bin/perl | |
784 | eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}' | |
785 | if $running_under_some_shell; | |
786 | ||
787 | The system ignores the first line and feeds the program to F</bin/sh>, | |
788 | which proceeds to try to execute the Perl program as a shell script. | |
789 | The shell executes the second line as a normal shell command, and thus | |
790 | starts up the Perl interpreter. On some systems $0 doesn't always | |
791 | contain the full pathname, so the B<-S> tells Perl to search for the | |
792 | program if necessary. After Perl locates the program, it parses the | |
793 | lines and ignores them because the variable $running_under_some_shell | |
794 | is never true. If the program will be interpreted by csh, you will need | |
795 | to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand | |
796 | embedded spaces (and such) in the argument list. To start up sh rather | |
797 | than csh, some systems may have to replace the #! line with a line | |
798 | containing just a colon, which will be politely ignored by Perl. Other | |
799 | systems can't control that, and need a totally devious construct that | |
800 | will work under any of B<csh>, B<sh>, or Perl, such as the following: | |
801 | ||
802 | eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}' | |
803 | & eval 'exec /usr/bin/perl -wS $0 $argv:q' | |
804 | if $running_under_some_shell; | |
805 | ||
806 | If the filename supplied contains directory separators (i.e., is an | |
807 | absolute or relative pathname), and if that file is not found, | |
808 | platforms that append file extensions will do so and try to look | |
809 | for the file with those extensions added, one by one. | |
810 | ||
811 | On DOS-like platforms, if the program does not contain directory | |
812 | separators, it will first be searched for in the current directory | |
813 | before being searched for on the PATH. On Unix platforms, the | |
814 | program will be searched for strictly on the PATH. | |
815 | ||
816 | =item B<-t> | |
817 | X<-t> | |
818 | ||
819 | Like B<-T>, but taint checks will issue warnings rather than fatal | |
820 | errors. These warnings can be controlled normally with C<no warnings | |
821 | qw(taint)>. | |
822 | ||
823 | B<NOTE: this is not a substitute for -T.> This is meant only to be | |
824 | used as a temporary development aid while securing legacy code: | |
825 | for real production code and for new secure code written from scratch | |
826 | always use the real B<-T>. | |
827 | ||
828 | =item B<-T> | |
829 | X<-T> | |
830 | ||
831 | forces "taint" checks to be turned on so you can test them. Ordinarily | |
832 | these checks are done only when running setuid or setgid. It's a | |
833 | good idea to turn them on explicitly for programs that run on behalf | |
834 | of someone else whom you might not necessarily trust, such as CGI | |
835 | programs or any internet servers you might write in Perl. See | |
836 | L<perlsec> for details. For security reasons, this option must be | |
837 | seen by Perl quite early; usually this means it must appear early | |
838 | on the command line or in the #! line for systems which support | |
839 | that construct. | |
840 | ||
841 | =item B<-u> | |
842 | X<-u> | |
843 | ||
844 | This obsolete switch causes Perl to dump core after compiling your | |
845 | program. You can then in theory take this core dump and turn it | |
846 | into an executable file by using the B<undump> program (not supplied). | |
847 | This speeds startup at the expense of some disk space (which you | |
848 | can minimize by stripping the executable). (Still, a "hello world" | |
849 | executable comes out to about 200K on my machine.) If you want to | |
850 | execute a portion of your program before dumping, use the dump() | |
851 | operator instead. Note: availability of B<undump> is platform | |
852 | specific and may not be available for a specific port of Perl. | |
853 | ||
854 | This switch has been superseded in favor of the new Perl code | |
855 | generator backends to the compiler. See L<B> and L<B::Bytecode> | |
856 | for details. | |
857 | ||
858 | =item B<-U> | |
859 | X<-U> | |
860 | ||
861 | allows Perl to do unsafe operations. Currently the only "unsafe" | |
862 | operations are attempting to unlink directories while running as | |
863 | superuser, and running setuid programs with fatal taint checks turned | |
864 | into warnings. Note that the B<-w> switch (or the C<$^W> variable) | |
865 | must be used along with this option to actually I<generate> the | |
866 | taint-check warnings. | |
867 | ||
868 | =item B<-v> | |
869 | X<-v> | |
870 | ||
871 | prints the version and patchlevel of your perl executable. | |
872 | ||
873 | =item B<-V> | |
874 | X<-V> | |
875 | ||
876 | prints summary of the major perl configuration values and the current | |
877 | values of @INC. | |
878 | ||
879 | =item B<-V:>I<configvar> | |
880 | ||
881 | Prints to STDOUT the value of the named configuration variable(s), | |
882 | with multiples when your configvar argument looks like a regex (has | |
883 | non-letters). For example: | |
884 | ||
885 | $ perl -V:libc | |
886 | libc='/lib/libc-2.2.4.so'; | |
887 | $ perl -V:lib. | |
888 | libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc'; | |
889 | libc='/lib/libc-2.2.4.so'; | |
890 | $ perl -V:lib.* | |
891 | libpth='/usr/local/lib /lib /usr/lib'; | |
892 | libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc'; | |
893 | lib_ext='.a'; | |
894 | libc='/lib/libc-2.2.4.so'; | |
895 | libperl='libperl.a'; | |
896 | .... | |
897 | ||
898 | Additionally, extra colons can be used to control formatting. A | |
899 | trailing colon suppresses the linefeed and terminator ';', allowing | |
900 | you to embed queries into shell commands. (mnemonic: PATH separator | |
901 | ':'.) | |
902 | ||
903 | $ echo "compression-vars: " `perl -V:z.*: ` " are here !" | |
904 | compression-vars: zcat='' zip='zip' are here ! | |
905 | ||
906 | A leading colon removes the 'name=' part of the response, this allows | |
907 | you to map to the name you need. (mnemonic: empty label) | |
908 | ||
909 | $ echo "goodvfork="`./perl -Ilib -V::usevfork` | |
910 | goodvfork=false; | |
911 | ||
912 | Leading and trailing colons can be used together if you need | |
913 | positional parameter values without the names. Note that in the case | |
914 | below, the PERL_API params are returned in alphabetical order. | |
915 | ||
916 | $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now | |
917 | building_on 'linux' '5' '1' '9' now | |
918 | ||
919 | =item B<-w> | |
920 | X<-w> | |
921 | ||
922 | prints warnings about dubious constructs, such as variable names | |
923 | that are mentioned only once and scalar variables that are used | |
924 | before being set, redefined subroutines, references to undefined | |
925 | filehandles or filehandles opened read-only that you are attempting | |
926 | to write on, values used as a number that don't look like numbers, | |
927 | using an array as though it were a scalar, if your subroutines | |
928 | recurse more than 100 deep, and innumerable other things. | |
929 | ||
930 | This switch really just enables the internal C<$^W> variable. You | |
931 | can disable or promote into fatal errors specific warnings using | |
932 | C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>. | |
933 | See also L<perldiag> and L<perltrap>. A new, fine-grained warning | |
934 | facility is also available if you want to manipulate entire classes | |
935 | of warnings; see L<warnings> or L<perllexwarn>. | |
936 | ||
937 | =item B<-W> | |
938 | X<-W> | |
939 | ||
940 | Enables all warnings regardless of C<no warnings> or C<$^W>. | |
941 | See L<perllexwarn>. | |
942 | ||
943 | =item B<-X> | |
944 | X<-X> | |
945 | ||
946 | Disables all warnings regardless of C<use warnings> or C<$^W>. | |
947 | See L<perllexwarn>. | |
948 | ||
949 | =item B<-x> | |
950 | X<-x> | |
951 | ||
952 | =item B<-x> I<directory> | |
953 | ||
954 | tells Perl that the program is embedded in a larger chunk of unrelated | |
955 | ASCII text, such as in a mail message. Leading garbage will be | |
956 | discarded until the first line that starts with #! and contains the | |
957 | string "perl". Any meaningful switches on that line will be applied. | |
958 | If a directory name is specified, Perl will switch to that directory | |
959 | before running the program. The B<-x> switch controls only the | |
960 | disposal of leading garbage. The program must be terminated with | |
961 | C<__END__> if there is trailing garbage to be ignored (the program | |
962 | can process any or all of the trailing garbage via the DATA filehandle | |
963 | if desired). | |
964 | ||
965 | =back | |
966 | ||
967 | =head1 ENVIRONMENT | |
968 | X<perl, environment variables> | |
969 | ||
970 | =over 12 | |
971 | ||
972 | =item HOME | |
973 | X<HOME> | |
974 | ||
975 | Used if chdir has no argument. | |
976 | ||
977 | =item LOGDIR | |
978 | X<LOGDIR> | |
979 | ||
980 | Used if chdir has no argument and HOME is not set. | |
981 | ||
982 | =item PATH | |
983 | X<PATH> | |
984 | ||
985 | Used in executing subprocesses, and in finding the program if B<-S> is | |
986 | used. | |
987 | ||
988 | =item PERL5LIB | |
989 | X<PERL5LIB> | |
990 | ||
991 | A list of directories in which to look for Perl library | |
992 | files before looking in the standard library and the current | |
993 | directory. Any architecture-specific directories under the specified | |
994 | locations are automatically included if they exist. If PERL5LIB is not | |
995 | defined, PERLLIB is used. Directories are separated (like in PATH) by | |
996 | a colon on unixish platforms and by a semicolon on Windows (the proper | |
997 | path separator being given by the command C<perl -V:path_sep>). | |
998 | ||
999 | When running taint checks (either because the program was running setuid | |
1000 | or setgid, or the B<-T> switch was used), neither variable is used. | |
1001 | The program should instead say: | |
1002 | ||
1003 | use lib "/my/directory"; | |
1004 | ||
1005 | =item PERL5OPT | |
1006 | X<PERL5OPT> | |
1007 | ||
1008 | Command-line options (switches). Switches in this variable are taken | |
1009 | as if they were on every Perl command line. Only the B<-[DIMUdmtw]> | |
1010 | switches are allowed. When running taint checks (because the program | |
1011 | was running setuid or setgid, or the B<-T> switch was used), this | |
1012 | variable is ignored. If PERL5OPT begins with B<-T>, tainting will be | |
1013 | enabled, and any subsequent options ignored. | |
1014 | ||
1015 | =item PERLIO | |
1016 | X<PERLIO> | |
1017 | ||
1018 | A space (or colon) separated list of PerlIO layers. If perl is built | |
1019 | to use PerlIO system for IO (the default) these layers effect perl's IO. | |
1020 | ||
1021 | It is conventional to start layer names with a colon e.g. C<:perlio> to | |
1022 | emphasise their similarity to variable "attributes". But the code that parses | |
1023 | layer specification strings (which is also used to decode the PERLIO | |
1024 | environment variable) treats the colon as a separator. | |
1025 | ||
1026 | An unset or empty PERLIO is equivalent to C<:stdio>. | |
1027 | ||
1028 | The list becomes the default for I<all> perl's IO. Consequently only built-in | |
1029 | layers can appear in this list, as external layers (such as :encoding()) need | |
1030 | IO in order to load them!. See L<"open pragma"|open> for how to add external | |
1031 | encodings as defaults. | |
1032 | ||
1033 | The layers that it makes sense to include in the PERLIO environment | |
1034 | variable are briefly summarised below. For more details see L<PerlIO>. | |
1035 | ||
1036 | =over 8 | |
1037 | ||
1038 | =item :bytes | |
1039 | X<:bytes> | |
1040 | ||
1041 | A pseudolayer that turns I<off> the C<:utf8> flag for the layer below. | |
1042 | Unlikely to be useful on its own in the global PERLIO environment variable. | |
1043 | You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>. | |
1044 | ||
1045 | =item :crlf | |
1046 | X<:crlf> | |
1047 | ||
1048 | A layer which does CRLF to "\n" translation distinguishing "text" and | |
1049 | "binary" files in the manner of MS-DOS and similar operating systems. | |
1050 | (It currently does I<not> mimic MS-DOS as far as treating of Control-Z | |
1051 | as being an end-of-file marker.) | |
1052 | ||
1053 | =item :mmap | |
1054 | X<:mmap> | |
1055 | ||
1056 | A layer which implements "reading" of files by using C<mmap()> to | |
1057 | make (whole) file appear in the process's address space, and then | |
1058 | using that as PerlIO's "buffer". | |
1059 | ||
1060 | =item :perlio | |
1061 | X<:perlio> | |
1062 | ||
1063 | This is a re-implementation of "stdio-like" buffering written as a | |
1064 | PerlIO "layer". As such it will call whatever layer is below it for | |
1065 | its operations (typically C<:unix>). | |
1066 | ||
1067 | =item :pop | |
1068 | X<:pop> | |
1069 | ||
1070 | An experimental pseudolayer that removes the topmost layer. | |
1071 | Use with the same care as is reserved for nitroglycerin. | |
1072 | ||
1073 | =item :raw | |
1074 | X<:raw> | |
1075 | ||
1076 | A pseudolayer that manipulates other layers. Applying the C<:raw> | |
1077 | layer is equivalent to calling C<binmode($fh)>. It makes the stream | |
1078 | pass each byte as-is without any translation. In particular CRLF | |
1079 | translation, and/or :utf8 intuited from locale are disabled. | |
1080 | ||
1081 | Unlike in the earlier versions of Perl C<:raw> is I<not> | |
1082 | just the inverse of C<:crlf> - other layers which would affect the | |
1083 | binary nature of the stream are also removed or disabled. | |
1084 | ||
1085 | =item :stdio | |
1086 | X<:stdio> | |
1087 | ||
1088 | This layer provides PerlIO interface by wrapping system's ANSI C "stdio" | |
1089 | library calls. The layer provides both buffering and IO. | |
1090 | Note that C<:stdio> layer does I<not> do CRLF translation even if that | |
1091 | is platforms normal behaviour. You will need a C<:crlf> layer above it | |
1092 | to do that. | |
1093 | ||
1094 | =item :unix | |
1095 | X<:unix> | |
1096 | ||
1097 | Low level layer which calls C<read>, C<write> and C<lseek> etc. | |
1098 | ||
1099 | =item :utf8 | |
1100 | X<:utf8> | |
1101 | ||
1102 | A pseudolayer that turns on a flag on the layer below to tell perl | |
1103 | that output should be in utf8 and that input should be regarded as | |
1104 | already in utf8 form. May be useful in PERLIO environment | |
1105 | variable to make UTF-8 the default. (To turn off that behaviour | |
1106 | use C<:bytes> layer.) | |
1107 | ||
1108 | =item :win32 | |
1109 | X<:win32> | |
1110 | ||
1111 | On Win32 platforms this I<experimental> layer uses native "handle" IO | |
1112 | rather than unix-like numeric file descriptor layer. Known to be | |
1113 | buggy in this release. | |
1114 | ||
1115 | =back | |
1116 | ||
1117 | On all platforms the default set of layers should give acceptable results. | |
1118 | ||
1119 | For UNIX platforms that will equivalent of "unix perlio" or "stdio". | |
1120 | Configure is setup to prefer "stdio" implementation if system's library | |
1121 | provides for fast access to the buffer, otherwise it uses the "unix perlio" | |
1122 | implementation. | |
1123 | ||
1124 | On Win32 the default in this release is "unix crlf". Win32's "stdio" | |
1125 | has a number of bugs/mis-features for perl IO which are somewhat | |
1126 | C compiler vendor/version dependent. Using our own C<crlf> layer as | |
1127 | the buffer avoids those issues and makes things more uniform. | |
1128 | The C<crlf> layer provides CRLF to/from "\n" conversion as well as | |
1129 | buffering. | |
1130 | ||
1131 | This release uses C<unix> as the bottom layer on Win32 and so still uses C | |
1132 | compiler's numeric file descriptor routines. There is an experimental native | |
1133 | C<win32> layer which is expected to be enhanced and should eventually be | |
1134 | the default under Win32. | |
1135 | ||
1136 | =item PERLIO_DEBUG | |
1137 | X<PERLIO_DEBUG> | |
1138 | ||
1139 | If set to the name of a file or device then certain operations of PerlIO | |
1140 | sub-system will be logged to that file (opened as append). Typical uses | |
1141 | are UNIX: | |
1142 | ||
1143 | PERLIO_DEBUG=/dev/tty perl script ... | |
1144 | ||
1145 | and Win32 approximate equivalent: | |
1146 | ||
1147 | set PERLIO_DEBUG=CON | |
1148 | perl script ... | |
1149 | ||
1150 | This functionality is disabled for setuid scripts and for scripts run | |
1151 | with B<-T>. | |
1152 | ||
1153 | =item PERLLIB | |
1154 | X<PERLLIB> | |
1155 | ||
1156 | A list of directories in which to look for Perl library | |
1157 | files before looking in the standard library and the current directory. | |
1158 | If PERL5LIB is defined, PERLLIB is not used. | |
1159 | ||
1160 | =item PERL5DB | |
1161 | X<PERL5DB> | |
1162 | ||
1163 | The command used to load the debugger code. The default is: | |
1164 | ||
1165 | BEGIN { require 'perl5db.pl' } | |
1166 | ||
1167 | =item PERL5DB_THREADED | |
1168 | X<PERL5DB_THREADED> | |
1169 | ||
1170 | If set to a true value, indicates to the debugger that the code being | |
1171 | debugged uses threads. | |
1172 | ||
1173 | =item PERL5SHELL (specific to the Win32 port) | |
1174 | X<PERL5SHELL> | |
1175 | ||
1176 | May be set to an alternative shell that perl must use internally for | |
1177 | executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c> | |
1178 | on WindowsNT and C<command.com /c> on Windows95. The value is considered | |
1179 | to be space-separated. Precede any character that needs to be protected | |
1180 | (like a space or backslash) with a backslash. | |
1181 | ||
1182 | Note that Perl doesn't use COMSPEC for this purpose because | |
1183 | COMSPEC has a high degree of variability among users, leading to | |
1184 | portability concerns. Besides, perl can use a shell that may not be | |
1185 | fit for interactive use, and setting COMSPEC to such a shell may | |
1186 | interfere with the proper functioning of other programs (which usually | |
1187 | look in COMSPEC to find a shell fit for interactive use). | |
1188 | ||
1189 | =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port) | |
1190 | X<PERL_ALLOW_NON_IFS_LSP> | |
1191 | ||
1192 | Set to 1 to allow the use of non-IFS compatible LSP's. | |
1193 | Perl normally searches for an IFS-compatible LSP because this is required | |
1194 | for its emulation of Windows sockets as real filehandles. However, this may | |
1195 | cause problems if you have a firewall such as McAfee Guardian which requires | |
1196 | all applications to use its LSP which is not IFS-compatible, because clearly | |
1197 | Perl will normally avoid using such an LSP. | |
1198 | Setting this environment variable to 1 means that Perl will simply use the | |
1199 | first suitable LSP enumerated in the catalog, which keeps McAfee Guardian | |
1200 | happy (and in that particular case Perl still works too because McAfee | |
1201 | Guardian's LSP actually plays some other games which allow applications | |
1202 | requiring IFS compatibility to work). | |
1203 | ||
1204 | =item PERL_DEBUG_MSTATS | |
1205 | X<PERL_DEBUG_MSTATS> | |
1206 | ||
1207 | Relevant only if perl is compiled with the malloc included with the perl | |
1208 | distribution (that is, if C<perl -V:d_mymalloc> is 'define'). | |
1209 | If set, this causes memory statistics to be dumped after execution. If set | |
1210 | to an integer greater than one, also causes memory statistics to be dumped | |
1211 | after compilation. | |
1212 | ||
1213 | =item PERL_DESTRUCT_LEVEL | |
1214 | X<PERL_DESTRUCT_LEVEL> | |
1215 | ||
1216 | Relevant only if your perl executable was built with B<-DDEBUGGING>, | |
1217 | this controls the behavior of global destruction of objects and other | |
1218 | references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information. | |
1219 | ||
1220 | =item PERL_DL_NONLAZY | |
1221 | X<PERL_DL_NONLAZY> | |
1222 | ||
1223 | Set to one to have perl resolve B<all> undefined symbols when it loads | |
1224 | a dynamic library. The default behaviour is to resolve symbols when | |
1225 | they are used. Setting this variable is useful during testing of | |
1226 | extensions as it ensures that you get an error on misspelled function | |
1227 | names even if the test suite doesn't call it. | |
1228 | ||
1229 | =item PERL_ENCODING | |
1230 | X<PERL_ENCODING> | |
1231 | ||
1232 | If using the C<encoding> pragma without an explicit encoding name, the | |
1233 | PERL_ENCODING environment variable is consulted for an encoding name. | |
1234 | ||
1235 | =item PERL_HASH_SEED | |
1236 | X<PERL_HASH_SEED> | |
1237 | ||
1238 | (Since Perl 5.8.1.) Used to randomise Perl's internal hash function. | |
1239 | To emulate the pre-5.8.1 behaviour, set to an integer (zero means | |
1240 | exactly the same order as 5.8.0). "Pre-5.8.1" means, among other | |
1241 | things, that hash keys will be ordered the same between different runs | |
1242 | of Perl. | |
1243 | ||
1244 | The default behaviour is to randomise unless the PERL_HASH_SEED is set. | |
1245 | If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default | |
1246 | behaviour is B<not> to randomise unless the PERL_HASH_SEED is set. | |
1247 | ||
1248 | If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses | |
1249 | the pseudorandom seed supplied by the operating system and libraries. | |
1250 | This means that each different run of Perl will have a different | |
1251 | ordering of the results of keys(), values(), and each(). | |
1252 | ||
1253 | B<Please note that the hash seed is sensitive information>. Hashes are | |
1254 | randomized to protect against local and remote attacks against Perl | |
1255 | code. By manually setting a seed this protection may be partially or | |
1256 | completely lost. | |
1257 | ||
1258 | See L<perlsec/"Algorithmic Complexity Attacks"> and | |
1259 | L</PERL_HASH_SEED_DEBUG> for more information. | |
1260 | ||
1261 | =item PERL_HASH_SEED_DEBUG | |
1262 | X<PERL_HASH_SEED_DEBUG> | |
1263 | ||
1264 | (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of | |
1265 | the hash seed at the beginning of execution. This, combined with | |
1266 | L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic | |
1267 | behavior caused by hash randomization. | |
1268 | ||
1269 | B<Note that the hash seed is sensitive information>: by knowing it one | |
1270 | can craft a denial-of-service attack against Perl code, even remotely, | |
1271 | see L<perlsec/"Algorithmic Complexity Attacks"> for more information. | |
1272 | B<Do not disclose the hash seed> to people who don't need to know it. | |
1273 | See also hash_seed() of L<Hash::Util>. | |
1274 | ||
1275 | =item PERL_ROOT (specific to the VMS port) | |
1276 | X<PERL_ROOT> | |
1277 | ||
1278 | A translation concealed rooted logical name that contains perl and the | |
1279 | logical device for the @INC path on VMS only. Other logical names that | |
1280 | affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and | |
1281 | SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in | |
1282 | L<perlvms> and in F<README.vms> in the Perl source distribution. | |
1283 | ||
1284 | =item PERL_SIGNALS | |
1285 | X<PERL_SIGNALS> | |
1286 | ||
1287 | In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0 | |
1288 | signals behaviour (immediate but unsafe) is restored. If set to | |
1289 | C<safe> the safe (or deferred) signals are used. | |
1290 | See L<perlipc/"Deferred Signals (Safe Signals)">. | |
1291 | ||
1292 | =item PERL_UNICODE | |
1293 | X<PERL_UNICODE> | |
1294 | ||
1295 | Equivalent to the B<-C> command-line switch. Note that this is not | |
1296 | a boolean variable-- setting this to C<"1"> is not the right way to | |
1297 | "enable Unicode" (whatever that would mean). You can use C<"0"> to | |
1298 | "disable Unicode", though (or alternatively unset PERL_UNICODE in | |
1299 | your shell before starting Perl). See the description of the C<-C> | |
1300 | switch for more information. | |
1301 | ||
1302 | =item SYS$LOGIN (specific to the VMS port) | |
1303 | X<SYS$LOGIN> | |
1304 | ||
1305 | Used if chdir has no argument and HOME and LOGDIR are not set. | |
1306 | ||
1307 | =back | |
1308 | ||
1309 | Perl also has environment variables that control how Perl handles data | |
1310 | specific to particular natural languages. See L<perllocale>. | |
1311 | ||
1312 | Apart from these, Perl uses no other environment variables, except | |
1313 | to make them available to the program being executed, and to child | |
1314 | processes. However, programs running setuid would do well to execute | |
1315 | the following lines before doing anything else, just to keep people | |
1316 | honest: | |
1317 | ||
1318 | $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need | |
1319 | $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL}; | |
1320 | delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; |