Commit | Line | Data |
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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlrun - how to execute the Perl interpreter | |
4 | ||
5 | =head1 SYNOPSIS | |
6 | ||
672fde27 | 7 | B<perl> S<[ B<-sTtuUWX> ]> |
e0ebc809 | 8 | S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]> |
9 | S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]> | |
f2095865 | 10 | S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]> |
e0ebc809 | 11 | S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]> |
12 | S<[ B<-P> ]> | |
13 | S<[ B<-S> ]> | |
14 | S<[ B<-x>[I<dir>] ]> | |
15 | S<[ B<-i>[I<extension>] ]> | |
16 | S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...> | |
702815ca RGS |
17 | S<[ B<-A [I<assertions>] >]> |
18 | S<[ B<-C [I<number/list>] >]> | |
a0d0e21e LW |
19 | |
20 | =head1 DESCRIPTION | |
21 | ||
19799a22 GS |
22 | The normal way to run a Perl program is by making it directly |
23 | executable, or else by passing the name of the source file as an | |
24 | argument on the command line. (An interactive Perl environment | |
25 | is also possible--see L<perldebug> for details on how to do that.) | |
26 | Upon startup, Perl looks for your program in one of the following | |
a0d0e21e LW |
27 | places: |
28 | ||
29 | =over 4 | |
30 | ||
31 | =item 1. | |
32 | ||
33 | Specified line by line via B<-e> switches on the command line. | |
34 | ||
35 | =item 2. | |
36 | ||
37 | Contained in the file specified by the first filename on the command line. | |
a3cb178b GS |
38 | (Note that systems supporting the #! notation invoke interpreters this |
39 | way. See L<Location of Perl>.) | |
a0d0e21e LW |
40 | |
41 | =item 3. | |
42 | ||
5f05dabc | 43 | Passed in implicitly via standard input. This works only if there are |
19799a22 GS |
44 | no filename arguments--to pass arguments to a STDIN-read program you |
45 | must explicitly specify a "-" for the program name. | |
a0d0e21e LW |
46 | |
47 | =back | |
48 | ||
49 | With methods 2 and 3, Perl starts parsing the input file from the | |
50 | beginning, unless you've specified a B<-x> switch, in which case it | |
51 | scans for the first line starting with #! and containing the word | |
19799a22 | 52 | "perl", and starts there instead. This is useful for running a program |
a0d0e21e | 53 | embedded in a larger message. (In this case you would indicate the end |
19799a22 | 54 | of the program using the C<__END__> token.) |
a0d0e21e | 55 | |
5f05dabc | 56 | The #! line is always examined for switches as the line is being |
57 | parsed. Thus, if you're on a machine that allows only one argument | |
58 | with the #! line, or worse, doesn't even recognize the #! line, you | |
59 | still can get consistent switch behavior regardless of how Perl was | |
19799a22 GS |
60 | invoked, even if B<-x> was used to find the beginning of the program. |
61 | ||
62 | Because historically some operating systems silently chopped off | |
63 | kernel interpretation of the #! line after 32 characters, some | |
64 | switches may be passed in on the command line, and some may not; | |
65 | you could even get a "-" without its letter, if you're not careful. | |
66 | You probably want to make sure that all your switches fall either | |
67 | before or after that 32-character boundary. Most switches don't | |
68 | actually care if they're processed redundantly, but getting a "-" | |
69 | instead of a complete switch could cause Perl to try to execute | |
70 | standard input instead of your program. And a partial B<-I> switch | |
a0d0e21e LW |
71 | could also cause odd results. |
72 | ||
19799a22 GS |
73 | Some switches do care if they are processed twice, for instance |
74 | combinations of B<-l> and B<-0>. Either put all the switches after | |
75 | the 32-character boundary (if applicable), or replace the use of | |
76 | B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>. | |
fb73857a | 77 | |
a0d0e21e LW |
78 | Parsing of the #! switches starts wherever "perl" is mentioned in the line. |
79 | The sequences "-*" and "- " are specifically ignored so that you could, | |
80 | if you were so inclined, say | |
81 | ||
82 | #!/bin/sh -- # -*- perl -*- -p | |
19799a22 | 83 | eval 'exec perl -wS $0 ${1+"$@"}' |
5f05dabc | 84 | if $running_under_some_shell; |
a0d0e21e | 85 | |
44a4342c | 86 | to let Perl see the B<-p> switch. |
19799a22 GS |
87 | |
88 | A similar trick involves the B<env> program, if you have it. | |
89 | ||
90 | #!/usr/bin/env perl | |
91 | ||
92 | The examples above use a relative path to the perl interpreter, | |
93 | getting whatever version is first in the user's path. If you want | |
94 | a specific version of Perl, say, perl5.005_57, you should place | |
95 | that directly in the #! line's path. | |
a0d0e21e LW |
96 | |
97 | If the #! line does not contain the word "perl", the program named after | |
98 | the #! is executed instead of the Perl interpreter. This is slightly | |
99 | bizarre, but it helps people on machines that don't do #!, because they | |
19799a22 | 100 | can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then |
a0d0e21e LW |
101 | dispatch the program to the correct interpreter for them. |
102 | ||
19799a22 | 103 | After locating your program, Perl compiles the entire program to an |
a0d0e21e | 104 | internal form. If there are any compilation errors, execution of the |
19799a22 | 105 | program is not attempted. (This is unlike the typical shell script, |
54310121 | 106 | which might run part-way through before finding a syntax error.) |
a0d0e21e | 107 | |
19799a22 | 108 | If the program is syntactically correct, it is executed. If the program |
a0d0e21e LW |
109 | runs off the end without hitting an exit() or die() operator, an implicit |
110 | C<exit(0)> is provided to indicate successful completion. | |
111 | ||
68dc0745 | 112 | =head2 #! and quoting on non-Unix systems |
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 | ||
19799a22 | 124 | as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's |
68dc0745 | 125 | `extproc' handling). |
126 | ||
54310121 | 127 | =item MS-DOS |
68dc0745 | 128 | |
19799a22 | 129 | Create a batch file to run your program, and codify it in |
fd1adc71 | 130 | C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source |
68dc0745 | 131 | distribution for more information). |
132 | ||
133 | =item Win95/NT | |
134 | ||
6c6a61e2 | 135 | The Win95/NT installation, when using the ActiveState installer for Perl, |
c8db1d39 | 136 | will modify the Registry to associate the F<.pl> extension with the perl |
6c6a61e2 GS |
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. | |
68dc0745 | 141 | |
142 | =item Macintosh | |
143 | ||
19799a22 | 144 | A Macintosh perl program will have the appropriate Creator and |
68dc0745 | 145 | Type, so that double-clicking them will invoke the perl application. |
146 | ||
bd3fa61c CB |
147 | =item VMS |
148 | ||
149 | Put | |
150 | ||
151 | $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' ! | |
152 | $ exit++ + ++$status != 0 and $exit = $status = undef; | |
153 | ||
19799a22 GS |
154 | at the top of your program, where B<-mysw> are any command line switches you |
155 | want to pass to Perl. You can now invoke the program directly, by saying | |
156 | C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly | |
157 | via F<DCL$PATH> by just using the name of the program). | |
bd3fa61c CB |
158 | |
159 | This incantation is a bit much to remember, but Perl will display it for | |
160 | you if you say C<perl "-V:startperl">. | |
161 | ||
68dc0745 | 162 | =back |
163 | ||
164 | Command-interpreters on non-Unix systems have rather different ideas | |
165 | on quoting than Unix shells. You'll need to learn the special | |
166 | characters in your command-interpreter (C<*>, C<\> and C<"> are | |
167 | common) and how to protect whitespace and these characters to run | |
19799a22 | 168 | one-liners (see B<-e> below). |
68dc0745 | 169 | |
170 | On some systems, you may have to change single-quotes to double ones, | |
e6f03d26 | 171 | which you must I<not> do on Unix or Plan 9 systems. You might also |
68dc0745 | 172 | have to change a single % to a %%. |
173 | ||
174 | For example: | |
175 | ||
176 | # Unix | |
177 | perl -e 'print "Hello world\n"' | |
178 | ||
54310121 | 179 | # MS-DOS, etc. |
68dc0745 | 180 | perl -e "print \"Hello world\n\"" |
181 | ||
54310121 | 182 | # Macintosh |
68dc0745 | 183 | print "Hello world\n" |
184 | (then Run "Myscript" or Shift-Command-R) | |
185 | ||
186 | # VMS | |
187 | perl -e "print ""Hello world\n""" | |
188 | ||
19799a22 GS |
189 | The problem is that none of this is reliable: it depends on the |
190 | command and it is entirely possible neither works. If B<4DOS> were | |
191 | the command shell, this would probably work better: | |
68dc0745 | 192 | |
193 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
194 | ||
19799a22 | 195 | B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in |
68dc0745 | 196 | when nobody was looking, but just try to find documentation for its |
197 | quoting rules. | |
198 | ||
54310121 | 199 | Under the Macintosh, it depends which environment you are using. The MacPerl |
68dc0745 | 200 | shell, or MPW, is much like Unix shells in its support for several |
54310121 | 201 | quoting variants, except that it makes free use of the Macintosh's non-ASCII |
68dc0745 | 202 | characters as control characters. |
203 | ||
204 | There is no general solution to all of this. It's just a mess. | |
205 | ||
a3cb178b GS |
206 | =head2 Location of Perl |
207 | ||
208 | It may seem obvious to say, but Perl is useful only when users can | |
19799a22 GS |
209 | easily find it. When possible, it's good for both F</usr/bin/perl> |
210 | and F</usr/local/bin/perl> to be symlinks to the actual binary. If | |
211 | that can't be done, system administrators are strongly encouraged | |
212 | to put (symlinks to) perl and its accompanying utilities into a | |
213 | directory typically found along a user's PATH, or in some other | |
214 | obvious and convenient place. | |
215 | ||
216 | In this documentation, C<#!/usr/bin/perl> on the first line of the program | |
217 | will stand in for whatever method works on your system. You are | |
218 | advised to use a specific path if you care about a specific version. | |
a3cb178b | 219 | |
19799a22 | 220 | #!/usr/local/bin/perl5.00554 |
a3cb178b | 221 | |
19799a22 GS |
222 | or if you just want to be running at least version, place a statement |
223 | like this at the top of your program: | |
a0d0e21e | 224 | |
19799a22 | 225 | use 5.005_54; |
a0d0e21e | 226 | |
19799a22 GS |
227 | =head2 Command Switches |
228 | ||
229 | As with all standard commands, a single-character switch may be | |
230 | clustered with the following switch, if any. | |
231 | ||
232 | #!/usr/bin/perl -spi.orig # same as -s -p -i.orig | |
a0d0e21e LW |
233 | |
234 | Switches include: | |
235 | ||
236 | =over 5 | |
237 | ||
f2095865 | 238 | =item B<-0>[I<octal/hexadecimal>] |
a0d0e21e | 239 | |
f2095865 JH |
240 | specifies the input record separator (C<$/>) as an octal or |
241 | hexadecimal number. If there are no digits, the null character is the | |
242 | separator. Other switches may precede or follow the digits. For | |
243 | example, if you have a version of B<find> which can print filenames | |
244 | terminated by the null character, you can say this: | |
a0d0e21e | 245 | |
19799a22 | 246 | find . -name '*.orig' -print0 | perl -n0e unlink |
a0d0e21e LW |
247 | |
248 | The special value 00 will cause Perl to slurp files in paragraph mode. | |
5f05dabc | 249 | The value 0777 will cause Perl to slurp files whole because there is no |
f2095865 JH |
250 | legal byte with that value. |
251 | ||
252 | If you want to specify any Unicode character, use the hexadecimal | |
253 | format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits. | |
254 | (This means that you cannot use the C<-x> with a directory name that | |
255 | consists of hexadecimal digits.) | |
a0d0e21e | 256 | |
702815ca RGS |
257 | =item B<-A [I<assertions>]> |
258 | ||
259 | Activates the assertions given after the switch as a comma-separated | |
260 | list of assertion names. If no assertion name is given, activates all | |
261 | assertions. See L<assertions>. | |
262 | ||
a0d0e21e LW |
263 | =item B<-a> |
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 | ||
a05d7ebb | 280 | =item B<-C [I<number/list>]> |
46487f74 | 281 | |
a05d7ebb JH |
282 | The C<-C> flag controls some Unicode of the Perl Unicode features. |
283 | ||
284 | As of 5.8.1, the C<-C> can be followed either by a number or a list | |
f3f8427d | 285 | of option letters. The letters, their numeric values, and effects |
8aa8f774 | 286 | are as follows; listing the letters is equal to summing the numbers. |
9f21530f JH |
287 | |
288 | I 1 STDIN is assumed to be in UTF-8 | |
289 | O 2 STDOUT will be in UTF-8 | |
290 | E 4 STDERR will be in UTF-8 | |
291 | S 7 I + O + E | |
44505768 JH |
292 | i 8 UTF-8 is the default PerlIO layer for input streams |
293 | o 16 UTF-8 is the default PerlIO layer for output streams | |
9f21530f | 294 | D 24 i + o |
44505768 | 295 | A 32 the @ARGV elements are expected to be strings encoded in UTF-8 |
ce81ff12 | 296 | L 64 normally the "IOEioA" are unconditional, |
9f21530f | 297 | the L makes them conditional on the locale environment |
ce81ff12 JH |
298 | variables (the LC_ALL, LC_TYPE, and LANG, in the order |
299 | of decreasing precedence) -- if the variables indicate | |
300 | UTF-8, then the selected "IOEioA" are in effect | |
9f21530f JH |
301 | |
302 | For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both | |
303 | STDOUT and STDERR. Repeating letters is just redundant, not cumulative | |
304 | nor toggling. | |
a05d7ebb | 305 | |
44505768 JH |
306 | The C<io> options mean that any subsequent open() (or similar I/O |
307 | operations) will have the C<:utf8> PerlIO layer implicitly applied | |
308 | to them, in other words, UTF-8 is expected from any input stream, | |
309 | and UTF-8 is produced to any output stream. This is just the default, | |
310 | with explicit layers in open() and with binmode() one can manipulate | |
311 | streams as usual. | |
312 | ||
8aa8f774 JH |
313 | C<-C> on its own (not followed by any number or option list), or the |
314 | empty string C<""> for the C<$ENV{PERL_UNICODE}, has the same effect | |
ce81ff12 JH |
315 | as <-CSDL>. In other words, the standard I/O handles and the default |
316 | C<open()> layer are UTF-8-fied B<but> only if the locale environment | |
8aa8f774 | 317 | variables indicate a UTF-8 locale. This behaviour follows the |
5b4f334e | 318 | I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0. |
a05d7ebb | 319 | |
ab9e1bb7 | 320 | You can use C<-C0> (or C<"0"> for $ENV{PERL_UNICODE}) to explicitly |
5b4f334e | 321 | disable all the above Unicode features. |
fde18df1 | 322 | |
8aa8f774 | 323 | The read-only magic variable C<${^UNICODE}> reflects the numeric value |
ab9e1bb7 JH |
324 | of this setting. This is variable is set during Perl startup and is |
325 | thereafter read-only. If you want runtime effects, use the three-arg | |
2307c6d0 | 326 | open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>), |
ab9e1bb7 | 327 | and the C<open> pragma (see L<open>). |
fde18df1 JH |
328 | |
329 | (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch | |
330 | that enabled the use of Unicode-aware "wide system call" Win32 APIs. | |
331 | This feature was practically unused, however, and the command line | |
332 | switch was therefore "recycled".) | |
46487f74 | 333 | |
a0d0e21e LW |
334 | =item B<-c> |
335 | ||
19799a22 | 336 | causes Perl to check the syntax of the program and then exit without |
7d30b5c4 | 337 | executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and |
4f25aa18 GS |
338 | C<use> blocks, because these are considered as occurring outside the |
339 | execution of your program. C<INIT> and C<END> blocks, however, will | |
340 | be skipped. | |
a0d0e21e LW |
341 | |
342 | =item B<-d> | |
343 | ||
19799a22 | 344 | runs the program under the Perl debugger. See L<perldebug>. |
a0d0e21e | 345 | |
70c94a19 | 346 | =item B<-d:>I<foo[=bar,baz]> |
3c81428c | 347 | |
19799a22 GS |
348 | runs the program under the control of a debugging, profiling, or |
349 | tracing module installed as Devel::foo. E.g., B<-d:DProf> executes | |
70c94a19 RR |
350 | the program using the Devel::DProf profiler. As with the B<-M> |
351 | flag, options may be passed to the Devel::foo package where they | |
352 | will be received and interpreted by the Devel::foo::import routine. | |
353 | The comma-separated list of options must follow a C<=> character. | |
354 | See L<perldebug>. | |
3c81428c | 355 | |
db2ba183 | 356 | =item B<-D>I<letters> |
a0d0e21e | 357 | |
db2ba183 | 358 | =item B<-D>I<number> |
a0d0e21e | 359 | |
19799a22 | 360 | sets debugging flags. To watch how it executes your program, use |
db2ba183 TB |
361 | B<-Dtls>. (This works only if debugging is compiled into your |
362 | Perl.) Another nice value is B<-Dx>, which lists your compiled | |
4197b13f | 363 | syntax tree. And B<-Dr> displays compiled regular expressions; |
44a4342c | 364 | the format of the output is explained in L<perldebguts>. |
4197b13f MJD |
365 | |
366 | As an alternative, specify a number instead of list of letters (e.g., | |
367 | B<-D14> is equivalent to B<-Dtls>): | |
a0d0e21e | 368 | |
db2ba183 TB |
369 | 1 p Tokenizing and parsing |
370 | 2 s Stack snapshots | |
d6721266 | 371 | with v, displays all stacks |
db2ba183 TB |
372 | 4 l Context (loop) stack processing |
373 | 8 t Trace execution | |
374 | 16 o Method and overloading resolution | |
375 | 32 c String/numeric conversions | |
1045810a | 376 | 64 P Print profiling info, preprocessor command for -P, source file input state |
db2ba183 TB |
377 | 128 m Memory allocation |
378 | 256 f Format processing | |
379 | 512 r Regular expression parsing and execution | |
380 | 1024 x Syntax tree dump | |
381 | 2048 u Tainting checks | |
7bab3ede | 382 | 4096 (Obsolete, previously used for LEAKTEST) |
db2ba183 TB |
383 | 8192 H Hash dump -- usurps values() |
384 | 16384 X Scratchpad allocation | |
385 | 32768 D Cleaning up | |
8b73bbec | 386 | 65536 S Thread synchronization |
607df283 | 387 | 131072 T Tokenising |
04932ac8 | 388 | 262144 R Include reference counts of dumped variables (eg when using -Ds) |
1045810a | 389 | 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB |
d6721266 | 390 | 1048576 v Verbose: use in conjunction with other flags |
46187eeb | 391 | 2097152 C Copy On Write |
a0d0e21e | 392 | |
19799a22 | 393 | All these flags require B<-DDEBUGGING> when you compile the Perl |
1045810a | 394 | executable (but see L<Devel::Peek>, L<re> which may change this). |
44a4342c | 395 | See the F<INSTALL> file in the Perl source distribution |
19799a22 | 396 | for how to do this. This flag is automatically set if you include B<-g> |
8c52afec IZ |
397 | option when C<Configure> asks you about optimizer/debugger flags. |
398 | ||
19799a22 GS |
399 | If you're just trying to get a print out of each line of Perl code |
400 | as it executes, the way that C<sh -x> provides for shell scripts, | |
44a4342c | 401 | you can't use Perl's B<-D> switch. Instead do this |
19799a22 | 402 | |
c406981e JH |
403 | # If you have "env" utility |
404 | env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program | |
405 | ||
19799a22 GS |
406 | # Bourne shell syntax |
407 | $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program | |
408 | ||
409 | # csh syntax | |
410 | % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program) | |
411 | ||
412 | See L<perldebug> for details and variations. | |
413 | ||
a0d0e21e LW |
414 | =item B<-e> I<commandline> |
415 | ||
19799a22 GS |
416 | may be used to enter one line of program. If B<-e> is given, Perl |
417 | will not look for a filename in the argument list. Multiple B<-e> | |
418 | commands may be given to build up a multi-line script. Make sure | |
419 | to use semicolons where you would in a normal program. | |
a0d0e21e | 420 | |
e0ebc809 | 421 | =item B<-F>I<pattern> |
a0d0e21e | 422 | |
e0ebc809 | 423 | specifies the pattern to split on if B<-a> is also in effect. The |
5f05dabc | 424 | pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be |
e0ebc809 | 425 | put in single quotes. |
a0d0e21e | 426 | |
e0ebc809 | 427 | =item B<-h> |
428 | ||
429 | prints a summary of the options. | |
430 | ||
431 | =item B<-i>[I<extension>] | |
a0d0e21e | 432 | |
2d259d92 CK |
433 | specifies that files processed by the C<E<lt>E<gt>> construct are to be |
434 | edited in-place. It does this by renaming the input file, opening the | |
435 | output file by the original name, and selecting that output file as the | |
436 | default for print() statements. The extension, if supplied, is used to | |
437 | modify the name of the old file to make a backup copy, following these | |
438 | rules: | |
439 | ||
440 | If no extension is supplied, no backup is made and the current file is | |
441 | overwritten. | |
442 | ||
19799a22 GS |
443 | If the extension doesn't contain a C<*>, then it is appended to the |
444 | end of the current filename as a suffix. If the extension does | |
445 | contain one or more C<*> characters, then each C<*> is replaced | |
446 | with the current filename. In Perl terms, you could think of this | |
447 | as: | |
2d259d92 | 448 | |
66606d78 | 449 | ($backup = $extension) =~ s/\*/$file_name/g; |
2d259d92 CK |
450 | |
451 | This allows you to add a prefix to the backup file, instead of (or in | |
452 | addition to) a suffix: | |
453 | ||
19799a22 | 454 | $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA' |
2d259d92 CK |
455 | |
456 | Or even to place backup copies of the original files into another | |
457 | directory (provided the directory already exists): | |
458 | ||
19799a22 | 459 | $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig' |
2d259d92 | 460 | |
66606d78 CK |
461 | These sets of one-liners are equivalent: |
462 | ||
463 | $ perl -pi -e 's/bar/baz/' fileA # overwrite current file | |
19799a22 | 464 | $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file |
66606d78 | 465 | |
19799a22 GS |
466 | $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' |
467 | $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' | |
66606d78 | 468 | |
2d259d92 | 469 | From the shell, saying |
a0d0e21e | 470 | |
19799a22 | 471 | $ perl -p -i.orig -e "s/foo/bar/; ... " |
a0d0e21e | 472 | |
19799a22 | 473 | is the same as using the program: |
a0d0e21e | 474 | |
19799a22 | 475 | #!/usr/bin/perl -pi.orig |
a0d0e21e LW |
476 | s/foo/bar/; |
477 | ||
478 | which is equivalent to | |
479 | ||
480 | #!/usr/bin/perl | |
19799a22 GS |
481 | $extension = '.orig'; |
482 | LINE: while (<>) { | |
a0d0e21e | 483 | if ($ARGV ne $oldargv) { |
66606d78 CK |
484 | if ($extension !~ /\*/) { |
485 | $backup = $ARGV . $extension; | |
486 | } | |
487 | else { | |
488 | ($backup = $extension) =~ s/\*/$ARGV/g; | |
489 | } | |
490 | rename($ARGV, $backup); | |
a0d0e21e LW |
491 | open(ARGVOUT, ">$ARGV"); |
492 | select(ARGVOUT); | |
493 | $oldargv = $ARGV; | |
494 | } | |
495 | s/foo/bar/; | |
496 | } | |
497 | continue { | |
498 | print; # this prints to original filename | |
499 | } | |
500 | select(STDOUT); | |
501 | ||
502 | except that the B<-i> form doesn't need to compare $ARGV to $oldargv to | |
503 | know when the filename has changed. It does, however, use ARGVOUT for | |
66606d78 CK |
504 | the selected filehandle. Note that STDOUT is restored as the default |
505 | output filehandle after the loop. | |
506 | ||
507 | As shown above, Perl creates the backup file whether or not any output | |
508 | is actually changed. So this is just a fancy way to copy files: | |
509 | ||
cd2d1bac | 510 | $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3... |
19799a22 | 511 | or |
cd2d1bac | 512 | $ perl -p -i'.orig' -e 1 file1 file2 file3... |
66606d78 CK |
513 | |
514 | You can use C<eof> without parentheses to locate the end of each input | |
515 | file, in case you want to append to each file, or reset line numbering | |
516 | (see example in L<perlfunc/eof>). | |
517 | ||
518 | If, for a given file, Perl is unable to create the backup file as | |
519 | specified in the extension then it will skip that file and continue on | |
520 | with the next one (if it exists). | |
521 | ||
19799a22 | 522 | For a discussion of issues surrounding file permissions and B<-i>, |
cea6626f | 523 | 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?>. |
66606d78 CK |
524 | |
525 | You cannot use B<-i> to create directories or to strip extensions from | |
526 | files. | |
a0d0e21e | 527 | |
19799a22 GS |
528 | Perl does not expand C<~> in filenames, which is good, since some |
529 | folks use it for their backup files: | |
a0d0e21e | 530 | |
19799a22 GS |
531 | $ perl -pi~ -e 's/foo/bar/' file1 file2 file3... |
532 | ||
533 | Finally, the B<-i> switch does not impede execution when no | |
a2008d6d GS |
534 | files are given on the command line. In this case, no backup is made |
535 | (the original file cannot, of course, be determined) and processing | |
536 | proceeds from STDIN to STDOUT as might be expected. | |
537 | ||
a0d0e21e LW |
538 | =item B<-I>I<directory> |
539 | ||
e0ebc809 | 540 | Directories specified by B<-I> are prepended to the search path for |
1fef88e7 | 541 | modules (C<@INC>), and also tells the C preprocessor where to search for |
e0ebc809 | 542 | include files. The C preprocessor is invoked with B<-P>; by default it |
543 | searches /usr/include and /usr/lib/perl. | |
a0d0e21e | 544 | |
e0ebc809 | 545 | =item B<-l>[I<octnum>] |
a0d0e21e | 546 | |
19799a22 GS |
547 | enables automatic line-ending processing. It has two separate |
548 | effects. First, it automatically chomps C<$/> (the input record | |
549 | separator) when used with B<-n> or B<-p>. Second, it assigns C<$\> | |
550 | (the output record separator) to have the value of I<octnum> so | |
551 | that any print statements will have that separator added back on. | |
552 | If I<octnum> is omitted, sets C<$\> to the current value of | |
553 | C<$/>. For instance, to trim lines to 80 columns: | |
a0d0e21e LW |
554 | |
555 | perl -lpe 'substr($_, 80) = ""' | |
556 | ||
557 | Note that the assignment C<$\ = $/> is done when the switch is processed, | |
558 | so the input record separator can be different than the output record | |
559 | separator if the B<-l> switch is followed by a B<-0> switch: | |
560 | ||
561 | gnufind / -print0 | perl -ln0e 'print "found $_" if -p' | |
562 | ||
1fef88e7 | 563 | This sets C<$\> to newline and then sets C<$/> to the null character. |
a0d0e21e | 564 | |
e0ebc809 | 565 | =item B<-m>[B<->]I<module> |
566 | ||
567 | =item B<-M>[B<->]I<module> | |
c07a80fd | 568 | |
e0ebc809 | 569 | =item B<-M>[B<->]I<'module ...'> |
570 | ||
571 | =item B<-[mM]>[B<->]I<module=arg[,arg]...> | |
3c81428c | 572 | |
19799a22 GS |
573 | B<-m>I<module> executes C<use> I<module> C<();> before executing your |
574 | program. | |
3c81428c | 575 | |
19799a22 GS |
576 | B<-M>I<module> executes C<use> I<module> C<;> before executing your |
577 | program. You can use quotes to add extra code after the module name, | |
578 | e.g., C<'-Mmodule qw(foo bar)'>. | |
3c81428c | 579 | |
19799a22 | 580 | If the first character after the B<-M> or B<-m> is a dash (C<->) |
a5f75d66 AD |
581 | then the 'use' is replaced with 'no'. |
582 | ||
54310121 | 583 | A little builtin syntactic sugar means you can also say |
19799a22 GS |
584 | B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for |
585 | C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when | |
586 | importing symbols. The actual code generated by B<-Mmodule=foo,bar> is | |
e0ebc809 | 587 | C<use module split(/,/,q{foo,bar})>. Note that the C<=> form |
19799a22 | 588 | removes the distinction between B<-m> and B<-M>. |
3c81428c | 589 | |
a0d0e21e LW |
590 | =item B<-n> |
591 | ||
19799a22 | 592 | causes Perl to assume the following loop around your program, which |
a0d0e21e LW |
593 | makes it iterate over filename arguments somewhat like B<sed -n> or |
594 | B<awk>: | |
595 | ||
19799a22 | 596 | LINE: |
a0d0e21e | 597 | while (<>) { |
19799a22 | 598 | ... # your program goes here |
a0d0e21e LW |
599 | } |
600 | ||
601 | Note that the lines are not printed by default. See B<-p> to have | |
08e9d68e | 602 | lines printed. If a file named by an argument cannot be opened for |
19799a22 | 603 | some reason, Perl warns you about it and moves on to the next file. |
08e9d68e DD |
604 | |
605 | Here is an efficient way to delete all files older than a week: | |
a0d0e21e | 606 | |
19799a22 | 607 | find . -mtime +7 -print | perl -nle unlink |
a0d0e21e | 608 | |
19799a22 GS |
609 | This is faster than using the B<-exec> switch of B<find> because you don't |
610 | have to start a process on every filename found. It does suffer from | |
611 | the bug of mishandling newlines in pathnames, which you can fix if | |
44a4342c | 612 | you follow the example under B<-0>. |
a0d0e21e LW |
613 | |
614 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
19799a22 | 615 | the implicit program loop, just as in B<awk>. |
a0d0e21e LW |
616 | |
617 | =item B<-p> | |
618 | ||
19799a22 | 619 | causes Perl to assume the following loop around your program, which |
a0d0e21e LW |
620 | makes it iterate over filename arguments somewhat like B<sed>: |
621 | ||
622 | ||
19799a22 | 623 | LINE: |
a0d0e21e | 624 | while (<>) { |
19799a22 | 625 | ... # your program goes here |
a0d0e21e | 626 | } continue { |
08e9d68e | 627 | print or die "-p destination: $!\n"; |
a0d0e21e LW |
628 | } |
629 | ||
08e9d68e DD |
630 | If a file named by an argument cannot be opened for some reason, Perl |
631 | warns you about it, and moves on to the next file. Note that the | |
c2611fb3 | 632 | lines are printed automatically. An error occurring during printing is |
08e9d68e DD |
633 | treated as fatal. To suppress printing use the B<-n> switch. A B<-p> |
634 | overrides a B<-n> switch. | |
a0d0e21e LW |
635 | |
636 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
19799a22 | 637 | the implicit loop, just as in B<awk>. |
a0d0e21e LW |
638 | |
639 | =item B<-P> | |
640 | ||
079a94c4 JH |
641 | B<NOTE: Use of -P is strongly discouraged because of its inherent |
642 | problems, including poor portability.> | |
643 | ||
644 | This option causes your program to be run through the C preprocessor before | |
efdf3af0 | 645 | compilation by Perl. Because both comments and B<cpp> directives begin |
a0d0e21e | 646 | with the # character, you should avoid starting comments with any words |
efdf3af0 | 647 | recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">. |
079a94c4 JH |
648 | |
649 | If you're considering using C<-P>, you might also want to look at the | |
650 | Filter::cpp module from CPAN. | |
651 | ||
652 | The problems of -P include, but are not limited to: | |
653 | ||
654 | =over 10 | |
655 | ||
656 | =item * | |
657 | ||
658 | The C<#!> line is stripped, so any switches there don't apply. | |
659 | ||
660 | =item * | |
661 | ||
662 | A C<-P> on a C<#!> line doesn't work. | |
663 | ||
664 | =item * | |
665 | ||
666 | B<All> lines that begin with (whitespace and) a C<#> but | |
667 | do not look like cpp commands, are stripped, including anything | |
44a4342c | 668 | inside Perl strings, regular expressions, and here-docs . |
079a94c4 JH |
669 | |
670 | =item * | |
671 | ||
672 | In some platforms the C preprocessor knows too much: it knows about | |
673 | the C++ -style until-end-of-line comments starting with C<"//">. | |
efdf3af0 JH |
674 | This will cause problems with common Perl constructs like |
675 | ||
676 | s/foo//; | |
677 | ||
678 | because after -P this will became illegal code | |
679 | ||
680 | s/foo | |
681 | ||
682 | The workaround is to use some other quoting separator than C<"/">, | |
683 | like for example C<"!">: | |
684 | ||
685 | s!foo!!; | |
a0d0e21e | 686 | |
079a94c4 JH |
687 | |
688 | ||
689 | =item * | |
690 | ||
691 | It requires not only a working C preprocessor but also a working | |
692 | F<sed>. If not on UNIX, you are probably out of luck on this. | |
693 | ||
694 | =item * | |
695 | ||
696 | Script line numbers are not preserved. | |
697 | ||
698 | =item * | |
699 | ||
700 | The C<-x> does not work with C<-P>. | |
701 | ||
702 | =back | |
9a1f07e7 | 703 | |
a0d0e21e LW |
704 | =item B<-s> |
705 | ||
19799a22 GS |
706 | enables rudimentary switch parsing for switches on the command |
707 | line after the program name but before any filename arguments (or before | |
3bbcc830 JP |
708 | an argument of B<-->). This means you can have switches with two leading |
709 | dashes (B<--help>). Any switch found there is removed from @ARGV and sets the | |
19799a22 | 710 | corresponding variable in the Perl program. The following program |
3c0facb2 GS |
711 | prints "1" if the program is invoked with a B<-xyz> switch, and "abc" |
712 | if it is invoked with B<-xyz=abc>. | |
a0d0e21e LW |
713 | |
714 | #!/usr/bin/perl -s | |
3c0facb2 | 715 | if ($xyz) { print "$xyz\n" } |
a0d0e21e | 716 | |
3bbcc830 JP |
717 | Do note that B<--help> creates the variable ${-help}, which is not compliant |
718 | with C<strict refs>. | |
719 | ||
a0d0e21e LW |
720 | =item B<-S> |
721 | ||
722 | makes Perl use the PATH environment variable to search for the | |
19799a22 GS |
723 | program (unless the name of the program contains directory separators). |
724 | ||
2a92aaa0 GS |
725 | On some platforms, this also makes Perl append suffixes to the |
726 | filename while searching for it. For example, on Win32 platforms, | |
727 | the ".bat" and ".cmd" suffixes are appended if a lookup for the | |
728 | original name fails, and if the name does not already end in one | |
729 | of those suffixes. If your Perl was compiled with DEBUGGING turned | |
730 | on, using the -Dp switch to Perl shows how the search progresses. | |
731 | ||
2a92aaa0 GS |
732 | Typically this is used to emulate #! startup on platforms that |
733 | don't support #!. This example works on many platforms that | |
734 | have a shell compatible with Bourne shell: | |
a0d0e21e LW |
735 | |
736 | #!/usr/bin/perl | |
a3cb178b | 737 | eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}' |
a0d0e21e LW |
738 | if $running_under_some_shell; |
739 | ||
19799a22 GS |
740 | The system ignores the first line and feeds the program to F</bin/sh>, |
741 | which proceeds to try to execute the Perl program as a shell script. | |
a0d0e21e LW |
742 | The shell executes the second line as a normal shell command, and thus |
743 | starts up the Perl interpreter. On some systems $0 doesn't always | |
744 | contain the full pathname, so the B<-S> tells Perl to search for the | |
19799a22 | 745 | program if necessary. After Perl locates the program, it parses the |
a0d0e21e | 746 | lines and ignores them because the variable $running_under_some_shell |
19799a22 | 747 | is never true. If the program will be interpreted by csh, you will need |
a3cb178b GS |
748 | to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand |
749 | embedded spaces (and such) in the argument list. To start up sh rather | |
a0d0e21e LW |
750 | than csh, some systems may have to replace the #! line with a line |
751 | containing just a colon, which will be politely ignored by Perl. Other | |
752 | systems can't control that, and need a totally devious construct that | |
19799a22 | 753 | will work under any of B<csh>, B<sh>, or Perl, such as the following: |
a0d0e21e | 754 | |
19799a22 | 755 | eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}' |
a3cb178b | 756 | & eval 'exec /usr/bin/perl -wS $0 $argv:q' |
5f05dabc | 757 | if $running_under_some_shell; |
a0d0e21e | 758 | |
19799a22 GS |
759 | If the filename supplied contains directory separators (i.e., is an |
760 | absolute or relative pathname), and if that file is not found, | |
761 | platforms that append file extensions will do so and try to look | |
762 | for the file with those extensions added, one by one. | |
763 | ||
764 | On DOS-like platforms, if the program does not contain directory | |
765 | separators, it will first be searched for in the current directory | |
766 | before being searched for on the PATH. On Unix platforms, the | |
767 | program will be searched for strictly on the PATH. | |
768 | ||
6537fe72 MS |
769 | =item B<-t> |
770 | ||
771 | Like B<-T>, but taint checks will issue warnings rather than fatal | |
317ea90d MS |
772 | errors. These warnings can be controlled normally with C<no warnings |
773 | qw(taint)>. | |
1dbad523 JH |
774 | |
775 | B<NOTE: this is not a substitute for -T.> This is meant only to be | |
776 | used as a temporary development aid while securing legacy code: | |
777 | for real production code and for new secure code written from scratch | |
778 | always use the real B<-T>. | |
6537fe72 | 779 | |
a0d0e21e LW |
780 | =item B<-T> |
781 | ||
a3cb178b | 782 | forces "taint" checks to be turned on so you can test them. Ordinarily |
19799a22 GS |
783 | these checks are done only when running setuid or setgid. It's a |
784 | good idea to turn them on explicitly for programs that run on behalf | |
785 | of someone else whom you might not necessarily trust, such as CGI | |
786 | programs or any internet servers you might write in Perl. See | |
787 | L<perlsec> for details. For security reasons, this option must be | |
788 | seen by Perl quite early; usually this means it must appear early | |
789 | on the command line or in the #! line for systems which support | |
790 | that construct. | |
a0d0e21e LW |
791 | |
792 | =item B<-u> | |
793 | ||
19799a22 GS |
794 | This obsolete switch causes Perl to dump core after compiling your |
795 | program. You can then in theory take this core dump and turn it | |
796 | into an executable file by using the B<undump> program (not supplied). | |
797 | This speeds startup at the expense of some disk space (which you | |
798 | can minimize by stripping the executable). (Still, a "hello world" | |
799 | executable comes out to about 200K on my machine.) If you want to | |
800 | execute a portion of your program before dumping, use the dump() | |
801 | operator instead. Note: availability of B<undump> is platform | |
802 | specific and may not be available for a specific port of Perl. | |
803 | ||
804 | This switch has been superseded in favor of the new Perl code | |
805 | generator backends to the compiler. See L<B> and L<B::Bytecode> | |
806 | for details. | |
a0d0e21e LW |
807 | |
808 | =item B<-U> | |
809 | ||
810 | allows Perl to do unsafe operations. Currently the only "unsafe" | |
811 | operations are the unlinking of directories while running as superuser, | |
812 | and running setuid programs with fatal taint checks turned into | |
19799a22 GS |
813 | warnings. Note that the B<-w> switch (or the C<$^W> variable) must |
814 | be used along with this option to actually I<generate> the | |
fb73857a | 815 | taint-check warnings. |
a0d0e21e LW |
816 | |
817 | =item B<-v> | |
818 | ||
19799a22 | 819 | prints the version and patchlevel of your perl executable. |
a0d0e21e | 820 | |
3c81428c | 821 | =item B<-V> |
822 | ||
823 | prints summary of the major perl configuration values and the current | |
19799a22 | 824 | values of @INC. |
3c81428c | 825 | |
e0ebc809 | 826 | =item B<-V:>I<name> |
3c81428c | 827 | |
828 | Prints to STDOUT the value of the named configuration variable. | |
44a4342c | 829 | For example, |
3c81428c | 830 | |
19799a22 GS |
831 | $ perl -V:man.dir |
832 | ||
833 | will provide strong clues about what your MANPATH variable should | |
834 | be set to in order to access the Perl documentation. | |
a0d0e21e | 835 | |
19799a22 | 836 | =item B<-w> |
774d564b | 837 | |
19799a22 GS |
838 | prints warnings about dubious constructs, such as variable names |
839 | that are mentioned only once and scalar variables that are used | |
840 | before being set, redefined subroutines, references to undefined | |
841 | filehandles or filehandles opened read-only that you are attempting | |
842 | to write on, values used as a number that doesn't look like numbers, | |
843 | using an array as though it were a scalar, if your subroutines | |
844 | recurse more than 100 deep, and innumerable other things. | |
845 | ||
b40da996 | 846 | This switch really just enables the internal C<$^W> variable. You |
19799a22 GS |
847 | can disable or promote into fatal errors specific warnings using |
848 | C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>. | |
849 | See also L<perldiag> and L<perltrap>. A new, fine-grained warning | |
850 | facility is also available if you want to manipulate entire classes | |
9f1b1f2d | 851 | of warnings; see L<warnings> or L<perllexwarn>. |
a0d0e21e | 852 | |
0453d815 PM |
853 | =item B<-W> |
854 | ||
3c0facb2 | 855 | Enables all warnings regardless of C<no warnings> or C<$^W>. |
0453d815 PM |
856 | See L<perllexwarn>. |
857 | ||
858 | =item B<-X> | |
859 | ||
3c0facb2 | 860 | Disables all warnings regardless of C<use warnings> or C<$^W>. |
0453d815 PM |
861 | See L<perllexwarn>. |
862 | ||
a0d0e21e LW |
863 | =item B<-x> I<directory> |
864 | ||
19799a22 GS |
865 | tells Perl that the program is embedded in a larger chunk of unrelated |
866 | ASCII text, such as in a mail message. Leading garbage will be | |
867 | discarded until the first line that starts with #! and contains the | |
868 | string "perl". Any meaningful switches on that line will be applied. | |
869 | If a directory name is specified, Perl will switch to that directory | |
870 | before running the program. The B<-x> switch controls only the | |
871 | disposal of leading garbage. The program must be terminated with | |
872 | C<__END__> if there is trailing garbage to be ignored (the program | |
873 | can process any or all of the trailing garbage via the DATA filehandle | |
874 | if desired). | |
a0d0e21e | 875 | |
1e422769 | 876 | =back |
877 | ||
878 | =head1 ENVIRONMENT | |
879 | ||
880 | =over 12 | |
881 | ||
882 | =item HOME | |
883 | ||
884 | Used if chdir has no argument. | |
885 | ||
886 | =item LOGDIR | |
887 | ||
888 | Used if chdir has no argument and HOME is not set. | |
889 | ||
890 | =item PATH | |
891 | ||
19799a22 | 892 | Used in executing subprocesses, and in finding the program if B<-S> is |
1e422769 | 893 | used. |
894 | ||
895 | =item PERL5LIB | |
896 | ||
48b971ca | 897 | A list of directories in which to look for Perl library |
1e422769 | 898 | files before looking in the standard library and the current |
951ba7fe GS |
899 | directory. Any architecture-specific directories under the specified |
900 | locations are automatically included if they exist. If PERL5LIB is not | |
48b971ca RGS |
901 | defined, PERLLIB is used. Directories are separated (like in PATH) by |
902 | a colon on unixish platforms and by a semicolon on Windows (the proper | |
903 | path separator being given by the command C<perl -V:path_sep>). | |
951ba7fe GS |
904 | |
905 | When running taint checks (either because the program was running setuid | |
906 | or setgid, or the B<-T> switch was used), neither variable is used. | |
907 | The program should instead say: | |
1e422769 | 908 | |
909 | use lib "/my/directory"; | |
910 | ||
54310121 | 911 | =item PERL5OPT |
912 | ||
913 | Command-line options (switches). Switches in this variable are taken | |
1c4db469 | 914 | as if they were on every Perl command line. Only the B<-[DIMUdmtw]> |
19799a22 | 915 | switches are allowed. When running taint checks (because the program |
54310121 | 916 | was running setuid or setgid, or the B<-T> switch was used), this |
74288ac8 GS |
917 | variable is ignored. If PERL5OPT begins with B<-T>, tainting will be |
918 | enabled, and any subsequent options ignored. | |
54310121 | 919 | |
16537909 JH |
920 | =item PERLIO |
921 | ||
44a4342c | 922 | A space (or colon) separated list of PerlIO layers. If perl is built |
03d9e98a | 923 | to use PerlIO system for IO (the default) these layers effect perl's IO. |
44a4342c NIS |
924 | |
925 | It is conventional to start layer names with a colon e.g. C<:perlio> to | |
926 | emphasise their similarity to variable "attributes". But the code that parses | |
927 | layer specification strings (which is also used to decode the PERLIO | |
928 | environment variable) treats the colon as a separator. | |
929 | ||
3b0db4f9 JH |
930 | An unset or empty PERLIO is equivalent to C<:stdio>. |
931 | ||
44a4342c NIS |
932 | The list becomes the default for I<all> perl's IO. Consequently only built-in |
933 | layers can appear in this list, as external layers (such as :encoding()) need | |
934 | IO in order to load them!. See L<"open pragma"|open> for how to add external | |
935 | encodings as defaults. | |
936 | ||
937 | The layers that it makes sense to include in the PERLIO environment | |
938 | variable are summarised below. For more details see L<PerlIO>. | |
16537909 JH |
939 | |
940 | =over 8 | |
941 | ||
942 | =item :bytes | |
943 | ||
18aba96f JH |
944 | A pseudolayer that turns I<off> the C<:utf8> flag for the layer below. |
945 | Unlikely to be useful on its own in the global PERLIO environment variable. | |
946 | You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>. | |
16537909 JH |
947 | |
948 | =item :crlf | |
949 | ||
8229d19f JH |
950 | A layer that implements DOS/Windows like CRLF line endings. On read |
951 | converts pairs of CR,LF to a single "\n" newline character. On write | |
952 | converts each "\n" to a CR,LF pair. Note that this layer likes to be | |
953 | one of its kind: it silently ignores attempts to be pushed into the | |
954 | layer stack more than once. | |
955 | ||
956 | (Gory details follow) To be more exact what happens is this: after | |
957 | pushing itself to the stack, the C<:crlf> layer checks all the layers | |
958 | below itself to find the first layer that is capable of being a CRLF | |
959 | layer but is not yet enabled to be a CRLF layer. If it finds such a | |
960 | layer, it enables the CRLFness of that other deeper layer, and then | |
961 | pops itself off the stack. If not, fine, use the one we just pushed. | |
962 | ||
963 | The end result is that a C<:crlf> means "please enable the first CRLF | |
964 | layer you can find, and if you can't find one, here would be a good | |
965 | spot to place a new one." | |
966 | ||
44a4342c NIS |
967 | Based on the C<:perlio> layer. |
968 | ||
969 | =item :mmap | |
970 | ||
971 | A layer which implements "reading" of files by using C<mmap()> to | |
972 | make (whole) file appear in the process's address space, and then | |
973 | using that as PerlIO's "buffer". This I<may> be faster in certain | |
974 | circumstances for large files, and may result in less physical memory | |
975 | use when multiple processes are reading the same file. | |
16537909 | 976 | |
44a4342c NIS |
977 | Files which are not C<mmap()>-able revert to behaving like the C<:perlio> |
978 | layer. Writes also behave like C<:perlio> layer as C<mmap()> for write | |
979 | needs extra house-keeping (to extend the file) which negates any advantage. | |
16537909 | 980 | |
44a4342c | 981 | The C<:mmap> layer will not exist if platform does not support C<mmap()>. |
16537909 | 982 | |
44a4342c | 983 | =item :perlio |
16537909 | 984 | |
44a4342c NIS |
985 | A from scratch implementation of buffering for PerlIO. Provides fast |
986 | access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt> | |
987 | and in general attempts to minimize data copying. | |
16537909 | 988 | |
44a4342c | 989 | C<:perlio> will insert a C<:unix> layer below itself to do low level IO. |
16537909 | 990 | |
18aba96f JH |
991 | =item :pop |
992 | ||
993 | An experimental pseudolayer that removes the topmost layer. | |
994 | Use with the same care as is reserved for nitroglyserin. | |
995 | ||
44a4342c | 996 | =item :raw |
16537909 | 997 | |
18aba96f JH |
998 | A pseudolayer that manipulates other layers. Applying the <:raw> |
999 | layer is equivalent to calling C<binmode($fh)>. It makes the stream | |
1000 | pass each byte as-is without any translation. In particular CRLF | |
1001 | translation, and/or :utf8 intuited from locale are disabled. | |
1cbfc93d | 1002 | |
0226bbdb | 1003 | Arranges for all accesses go straight to the lowest buffered layer provided |
44a4342c | 1004 | by the configration. That is it strips off any layers above that layer. |
16537909 | 1005 | |
fae2c0fb RGS |
1006 | In Perl 5.6 and some books the C<:raw> layer (previously sometimes also |
1007 | referred to as a "discipline") is documented as the inverse of the | |
1008 | C<:crlf> layer. That is no longer the case - other layers which would | |
1009 | alter binary nature of the stream are also disabled. If you want UNIX | |
1010 | line endings on a platform that normally does CRLF translation, but still | |
1011 | want UTF-8 or encoding defaults the appropriate thing to do is to add | |
1012 | C<:perlio> to PERLIO environment variable. | |
16537909 | 1013 | |
44a4342c NIS |
1014 | =item :stdio |
1015 | ||
1016 | This layer provides PerlIO interface by wrapping system's ANSI C "stdio" | |
1017 | library calls. The layer provides both buffering and IO. | |
1018 | Note that C<:stdio> layer does I<not> do CRLF translation even if that | |
1019 | is platforms normal behaviour. You will need a C<:crlf> layer above it | |
1020 | to do that. | |
1021 | ||
1022 | =item :unix | |
1023 | ||
1024 | Lowest level layer which provides basic PerlIO operations in terms of | |
1025 | UNIX/POSIX numeric file descriptor calls | |
1026 | C<open(), read(), write(), lseek(), close()> | |
16537909 JH |
1027 | |
1028 | =item :utf8 | |
1029 | ||
18aba96f JH |
1030 | A pseudolayer that turns on a flag on the layer below to tell perl |
1031 | that data sent to the stream should be converted to perl internal | |
1032 | "utf8" form and that data from the stream should be considered as so | |
1033 | encoded. On ASCII based platforms the encoding is UTF-8 and on EBCDIC | |
1034 | platforms UTF-EBCDIC. May be useful in PERLIO environment variable to | |
1035 | make UTF-8 the default. (To turn off that behaviour use C<:bytes> | |
1036 | layer.) | |
44a4342c NIS |
1037 | |
1038 | =item :win32 | |
1039 | ||
ab4f7683 | 1040 | On Win32 platforms this I<experimental> layer uses native "handle" IO |
44a4342c NIS |
1041 | rather than unix-like numeric file descriptor layer. Known to be |
1042 | buggy in this release. | |
16537909 JH |
1043 | |
1044 | =back | |
1045 | ||
44a4342c NIS |
1046 | On all platforms the default set of layers should give acceptable results. |
1047 | ||
ab4f7683 | 1048 | For UNIX platforms that will equivalent of "unix perlio" or "stdio". |
44a4342c NIS |
1049 | Configure is setup to prefer "stdio" implementation if system's library |
1050 | provides for fast access to the buffer, otherwise it uses the "unix perlio" | |
1051 | implementation. | |
1052 | ||
1053 | On Win32 the default in this release is "unix crlf". Win32's "stdio" | |
1054 | has a number of bugs/mis-features for perl IO which are somewhat | |
99366417 | 1055 | C compiler vendor/version dependent. Using our own C<crlf> layer as |
44a4342c NIS |
1056 | the buffer avoids those issues and makes things more uniform. |
1057 | The C<crlf> layer provides CRLF to/from "\n" conversion as well as | |
1058 | buffering. | |
1059 | ||
1060 | This release uses C<unix> as the bottom layer on Win32 and so still uses C | |
1061 | compiler's numeric file descriptor routines. There is an experimental native | |
1062 | C<win32> layer which is expected to be enhanced and should eventually replace | |
1063 | the C<unix> layer. | |
1064 | ||
1065 | =item PERLIO_DEBUG | |
1066 | ||
1067 | If set to the name of a file or device then certain operations of PerlIO | |
1068 | sub-system will be logged to that file (opened as append). Typical uses | |
1069 | are UNIX: | |
1070 | ||
1071 | PERLIO_DEBUG=/dev/tty perl script ... | |
1072 | ||
1073 | and Win32 approximate equivalent: | |
1074 | ||
1075 | set PERLIO_DEBUG=CON | |
1076 | perl script ... | |
1077 | ||
16537909 | 1078 | |
1e422769 | 1079 | =item PERLLIB |
1080 | ||
48b971ca | 1081 | A list of directories in which to look for Perl library |
1e422769 | 1082 | files before looking in the standard library and the current directory. |
1083 | If PERL5LIB is defined, PERLLIB is not used. | |
1084 | ||
1085 | =item PERL5DB | |
1086 | ||
1087 | The command used to load the debugger code. The default is: | |
1088 | ||
1089 | BEGIN { require 'perl5db.pl' } | |
1090 | ||
19799a22 | 1091 | =item PERL5SHELL (specific to the Win32 port) |
174c211a GS |
1092 | |
1093 | May be set to an alternative shell that perl must use internally for | |
11998fdb | 1094 | executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c> |
ce1da67e | 1095 | on WindowsNT and C<command.com /c> on Windows95. The value is considered |
19799a22 | 1096 | to be space-separated. Precede any character that needs to be protected |
ce1da67e GS |
1097 | (like a space or backslash) with a backslash. |
1098 | ||
1099 | Note that Perl doesn't use COMSPEC for this purpose because | |
1100 | COMSPEC has a high degree of variability among users, leading to | |
1101 | portability concerns. Besides, perl can use a shell that may not be | |
1102 | fit for interactive use, and setting COMSPEC to such a shell may | |
1103 | interfere with the proper functioning of other programs (which usually | |
1104 | look in COMSPEC to find a shell fit for interactive use). | |
174c211a | 1105 | |
1e422769 | 1106 | =item PERL_DEBUG_MSTATS |
1107 | ||
67ce8856 | 1108 | Relevant only if perl is compiled with the malloc included with the perl |
a3cb178b GS |
1109 | distribution (that is, if C<perl -V:d_mymalloc> is 'define'). |
1110 | If set, this causes memory statistics to be dumped after execution. If set | |
1e422769 | 1111 | to an integer greater than one, also causes memory statistics to be dumped |
1112 | after compilation. | |
1113 | ||
1114 | =item PERL_DESTRUCT_LEVEL | |
1115 | ||
1116 | Relevant only if your perl executable was built with B<-DDEBUGGING>, | |
1117 | this controls the behavior of global destruction of objects and other | |
64cea5fd | 1118 | references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information. |
a0d0e21e | 1119 | |
5d170f3a JH |
1120 | =item PERL_ENCODING |
1121 | ||
1122 | If using the C<encoding> pragma without an explicit encoding name, the | |
1123 | PERL_ENCODING environment variable is consulted for an encoding name. | |
1124 | ||
504f80c1 JH |
1125 | =item PERL_HASH_SEED |
1126 | ||
183c3da1 | 1127 | (Since Perl 5.8.1.) Used to randomise Perl's internal hash function. |
4546b9e6 JH |
1128 | To emulate the pre-5.8.1 behaviour, set to an integer (zero means |
1129 | exactly the same order as 5.8.0). "Pre-5.8.1" means, among other | |
1130 | things, that hash keys will be ordered the same between different runs | |
1131 | of Perl. | |
504f80c1 | 1132 | |
4546b9e6 JH |
1133 | The default behaviour is to randomise unless the PERL_HASH_SEED is set. |
1134 | If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default | |
1135 | behaviour is B<not> to randomise unless the PERL_HASH_SEED is set. | |
504f80c1 JH |
1136 | |
1137 | If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses | |
1138 | the pseudorandom seed supplied by the operating system and libraries. | |
4546b9e6 JH |
1139 | This means that each different run of Perl will have a different |
1140 | ordering of the results of keys(), values(), and each(). | |
504f80c1 | 1141 | |
26a2d347 JH |
1142 | B<Please note that the hash seed is sensitive information>. Hashes are |
1143 | randomized to protect against local and remote attacks against Perl | |
1144 | code. By manually setting a seed this protection may be partially or | |
1145 | completely lost. | |
1146 | ||
1147 | See L<perlsec/"Algorithmic Complexity Attacks"> and | |
1148 | L</PERL_HASH_SEED_DEBUG> for more information. | |
504f80c1 | 1149 | |
2191697e JH |
1150 | =item PERL_HASH_SEED_DEBUG |
1151 | ||
e67b9e52 | 1152 | (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of |
26a2d347 JH |
1153 | the hash seed at the beginning of execution. This, combined with |
1154 | L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic | |
1155 | behavior caused by hash randomization. | |
1156 | ||
1157 | B<Note that the hash seed is sensitive information>: by knowing it one | |
1158 | can craft a denial-of-service attack against Perl code, even remotely, | |
1159 | see L<perlsec/"Algorithmic Complexity Attacks"> for more information. | |
e67b9e52 | 1160 | B<Do not disclose the hash seed> to people who don't need to know it. |
9a7034eb | 1161 | See also hash_seed() of L<Hash::Util>. |
2191697e | 1162 | |
3d0ae7ba GS |
1163 | =item PERL_ROOT (specific to the VMS port) |
1164 | ||
1165 | A translation concealed rooted logical name that contains perl and the | |
1166 | logical device for the @INC path on VMS only. Other logical names that | |
44a4342c NIS |
1167 | affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and |
1168 | SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in | |
3d0ae7ba GS |
1169 | L<perlvms> and in F<README.vms> in the Perl source distribution. |
1170 | ||
4ffa73a3 JH |
1171 | =item PERL_SIGNALS |
1172 | ||
1173 | In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0 | |
1174 | signals behaviour (immediate but unsafe) is restored. If set to | |
ec488bcf JH |
1175 | C<safe> the safe (or deferred) signals are used. |
1176 | See L<perlipc/"Deferred Signals (Safe signals)">. | |
4ffa73a3 | 1177 | |
a05d7ebb | 1178 | =item PERL_UNICODE |
acae81db | 1179 | |
bf61ac64 JH |
1180 | Equivalent to the B<-C> command-line switch. Note that this is not |
1181 | a boolean variable-- setting this to C<"1"> is not the right way to | |
5b4f334e | 1182 | "enable Unicode" (whatever that would mean). You can use C<"0"> to |
e654d908 JH |
1183 | "disable Unicode", though (or alternatively unset PERL_UNICODE in |
1184 | your shell before starting Perl). See the description of the C<-C> | |
1185 | switch for more information. | |
acae81db | 1186 | |
3d0ae7ba GS |
1187 | =item SYS$LOGIN (specific to the VMS port) |
1188 | ||
1189 | Used if chdir has no argument and HOME and LOGDIR are not set. | |
1190 | ||
a0d0e21e | 1191 | =back |
1e422769 | 1192 | |
1193 | Perl also has environment variables that control how Perl handles data | |
1194 | specific to particular natural languages. See L<perllocale>. | |
1195 | ||
1196 | Apart from these, Perl uses no other environment variables, except | |
19799a22 GS |
1197 | to make them available to the program being executed, and to child |
1198 | processes. However, programs running setuid would do well to execute | |
1e422769 | 1199 | the following lines before doing anything else, just to keep people |
1200 | honest: | |
1201 | ||
19799a22 | 1202 | $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need |
7bac28a0 | 1203 | $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL}; |
c90c0ff4 | 1204 | delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; |