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>] ]> |
2cbb2ee1 | 9 | S<[ B<-cw> ] [ B<-d>[B<t>][: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>] ]> |
df451b2a | 11 | S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]> |
c630fe62 | 12 | S<[ B<-C [I<number/list>] >]> |
e0ebc809 | 13 | S<[ B<-S> ]> |
14 | S<[ B<-x>[I<dir>] ]> | |
15 | S<[ B<-i>[I<extension>] ]> | |
eb1dd64e | 16 | S<[ [B<-e>|B<-E>] I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...> |
a0d0e21e LW |
17 | |
18 | =head1 DESCRIPTION | |
19 | ||
19799a22 GS |
20 | The normal way to run a Perl program is by making it directly |
21 | executable, or else by passing the name of the source file as an | |
22 | argument on the command line. (An interactive Perl environment | |
23 | is also possible--see L<perldebug> for details on how to do that.) | |
24 | Upon startup, Perl looks for your program in one of the following | |
a0d0e21e LW |
25 | places: |
26 | ||
27 | =over 4 | |
28 | ||
29 | =item 1. | |
30 | ||
bc9b29db | 31 | Specified line by line via B<-e> or B<-E> switches on the command line. |
a0d0e21e LW |
32 | |
33 | =item 2. | |
34 | ||
35 | Contained in the file specified by the first filename on the command line. | |
f4750dab | 36 | (Note that systems supporting the C<#!> notation invoke interpreters this |
a3cb178b | 37 | way. See L<Location of Perl>.) |
a0d0e21e LW |
38 | |
39 | =item 3. | |
40 | ||
5f05dabc | 41 | Passed in implicitly via standard input. This works only if there are |
19799a22 GS |
42 | no filename arguments--to pass arguments to a STDIN-read program you |
43 | must explicitly specify a "-" for the program name. | |
a0d0e21e LW |
44 | |
45 | =back | |
46 | ||
47 | With methods 2 and 3, Perl starts parsing the input file from the | |
48 | beginning, unless you've specified a B<-x> switch, in which case it | |
f4750dab | 49 | scans for the first line starting with C<#!> and containing the word |
19799a22 | 50 | "perl", and starts there instead. This is useful for running a program |
a0d0e21e | 51 | embedded in a larger message. (In this case you would indicate the end |
19799a22 | 52 | of the program using the C<__END__> token.) |
a0d0e21e | 53 | |
f4750dab | 54 | The C<#!> line is always examined for switches as the line is being |
5f05dabc | 55 | parsed. Thus, if you're on a machine that allows only one argument |
f4750dab TC |
56 | with the C<#!> line, or worse, doesn't even recognize the C<#!> line, you |
57 | still can get consistent switch behaviour regardless of how Perl was | |
19799a22 GS |
58 | invoked, even if B<-x> was used to find the beginning of the program. |
59 | ||
60 | Because historically some operating systems silently chopped off | |
f4750dab | 61 | kernel interpretation of the C<#!> line after 32 characters, some |
19799a22 GS |
62 | switches may be passed in on the command line, and some may not; |
63 | you could even get a "-" without its letter, if you're not careful. | |
64 | You probably want to make sure that all your switches fall either | |
65 | before or after that 32-character boundary. Most switches don't | |
66 | actually care if they're processed redundantly, but getting a "-" | |
67 | instead of a complete switch could cause Perl to try to execute | |
68 | standard input instead of your program. And a partial B<-I> switch | |
a0d0e21e LW |
69 | could also cause odd results. |
70 | ||
19799a22 GS |
71 | Some switches do care if they are processed twice, for instance |
72 | combinations of B<-l> and B<-0>. Either put all the switches after | |
73 | the 32-character boundary (if applicable), or replace the use of | |
74 | B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>. | |
fb73857a | 75 | |
f4750dab | 76 | Parsing of the C<#!> switches starts wherever "perl" is mentioned in the line. |
a0d0e21e LW |
77 | The sequences "-*" and "- " are specifically ignored so that you could, |
78 | if you were so inclined, say | |
79 | ||
428bacd7 SP |
80 | #!/bin/sh |
81 | #! -*-perl-*- | |
82 | eval 'exec perl -x -wS $0 ${1+"$@"}' | |
83 | if 0; | |
a0d0e21e | 84 | |
44a4342c | 85 | to let Perl see the B<-p> switch. |
19799a22 | 86 | |
f4750dab | 87 | A similar trick involves the I<env> program, if you have it. |
19799a22 GS |
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 | |
6898e867 | 93 | a specific version of Perl, say, perl5.14.1, you should place |
f4750dab | 94 | that directly in the C<#!> line's path. |
a0d0e21e | 95 | |
2f1fe8a3 RGS |
96 | If the C<#!> line does not contain the word "perl" nor the word "indir" |
97 | the program named after the C<#!> is executed instead of the Perl | |
98 | interpreter. This is slightly bizarre, but it helps people on machines | |
99 | that don't do C<#!>, because they can tell a program that their SHELL is | |
100 | F</usr/bin/perl>, and Perl will then dispatch the program to the correct | |
101 | interpreter for them. | |
a0d0e21e | 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 |
d74e8afc | 113 | X<hashbang> X<#!> |
68dc0745 | 114 | |
f4750dab | 115 | Unix's C<#!> technique can be simulated on other systems: |
68dc0745 | 116 | |
117 | =over 4 | |
118 | ||
119 | =item OS/2 | |
120 | ||
121 | Put | |
122 | ||
123 | extproc perl -S -your_switches | |
124 | ||
19799a22 | 125 | as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's |
68dc0745 | 126 | `extproc' handling). |
127 | ||
54310121 | 128 | =item MS-DOS |
68dc0745 | 129 | |
19799a22 | 130 | Create a batch file to run your program, and codify it in |
fd1adc71 | 131 | C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source |
68dc0745 | 132 | distribution for more information). |
133 | ||
134 | =item Win95/NT | |
135 | ||
6c6a61e2 | 136 | The Win95/NT installation, when using the ActiveState installer for Perl, |
c8db1d39 | 137 | will modify the Registry to associate the F<.pl> extension with the perl |
6c6a61e2 GS |
138 | interpreter. If you install Perl by other means (including building from |
139 | the sources), you may have to modify the Registry yourself. Note that | |
140 | this means you can no longer tell the difference between an executable | |
141 | Perl program and a Perl library file. | |
68dc0745 | 142 | |
bd3fa61c CB |
143 | =item VMS |
144 | ||
145 | Put | |
146 | ||
60b7c710 KW |
147 | $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' ! |
148 | $ exit++ + ++$status != 0 and $exit = $status = undef; | |
bd3fa61c | 149 | |
19799a22 GS |
150 | at the top of your program, where B<-mysw> are any command line switches you |
151 | want to pass to Perl. You can now invoke the program directly, by saying | |
152 | C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly | |
153 | via F<DCL$PATH> by just using the name of the program). | |
bd3fa61c CB |
154 | |
155 | This incantation is a bit much to remember, but Perl will display it for | |
156 | you if you say C<perl "-V:startperl">. | |
157 | ||
68dc0745 | 158 | =back |
159 | ||
160 | Command-interpreters on non-Unix systems have rather different ideas | |
161 | on quoting than Unix shells. You'll need to learn the special | |
162 | characters in your command-interpreter (C<*>, C<\> and C<"> are | |
163 | common) and how to protect whitespace and these characters to run | |
76c9ab0e | 164 | one-liners (see L<-e|/-e commandline> below). |
68dc0745 | 165 | |
166 | On some systems, you may have to change single-quotes to double ones, | |
e6f03d26 | 167 | which you must I<not> do on Unix or Plan 9 systems. You might also |
68dc0745 | 168 | have to change a single % to a %%. |
169 | ||
170 | For example: | |
171 | ||
172 | # Unix | |
173 | perl -e 'print "Hello world\n"' | |
174 | ||
54310121 | 175 | # MS-DOS, etc. |
68dc0745 | 176 | perl -e "print \"Hello world\n\"" |
177 | ||
68dc0745 | 178 | # VMS |
179 | perl -e "print ""Hello world\n""" | |
180 | ||
19799a22 | 181 | The problem is that none of this is reliable: it depends on the |
f4750dab | 182 | command and it is entirely possible neither works. If I<4DOS> were |
19799a22 | 183 | the command shell, this would probably work better: |
68dc0745 | 184 | |
185 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" | |
186 | ||
19799a22 | 187 | B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in |
68dc0745 | 188 | when nobody was looking, but just try to find documentation for its |
189 | quoting rules. | |
190 | ||
68dc0745 | 191 | There is no general solution to all of this. It's just a mess. |
192 | ||
a3cb178b | 193 | =head2 Location of Perl |
d74e8afc | 194 | X<perl, location of interpreter> |
a3cb178b GS |
195 | |
196 | It may seem obvious to say, but Perl is useful only when users can | |
19799a22 GS |
197 | easily find it. When possible, it's good for both F</usr/bin/perl> |
198 | and F</usr/local/bin/perl> to be symlinks to the actual binary. If | |
199 | that can't be done, system administrators are strongly encouraged | |
200 | to put (symlinks to) perl and its accompanying utilities into a | |
201 | directory typically found along a user's PATH, or in some other | |
202 | obvious and convenient place. | |
203 | ||
204 | In this documentation, C<#!/usr/bin/perl> on the first line of the program | |
205 | will stand in for whatever method works on your system. You are | |
206 | advised to use a specific path if you care about a specific version. | |
a3cb178b | 207 | |
6898e867 | 208 | #!/usr/local/bin/perl5.14 |
a3cb178b | 209 | |
19799a22 GS |
210 | or if you just want to be running at least version, place a statement |
211 | like this at the top of your program: | |
a0d0e21e | 212 | |
6898e867 | 213 | use 5.014; |
a0d0e21e | 214 | |
19799a22 | 215 | =head2 Command Switches |
d74e8afc | 216 | X<perl, command switches> X<command switches> |
19799a22 GS |
217 | |
218 | As with all standard commands, a single-character switch may be | |
219 | clustered with the following switch, if any. | |
220 | ||
221 | #!/usr/bin/perl -spi.orig # same as -s -p -i.orig | |
a0d0e21e LW |
222 | |
223 | Switches include: | |
224 | ||
225 | =over 5 | |
226 | ||
f2095865 | 227 | =item B<-0>[I<octal/hexadecimal>] |
d74e8afc | 228 | X<-0> X<$/> |
a0d0e21e | 229 | |
f2095865 JH |
230 | specifies the input record separator (C<$/>) as an octal or |
231 | hexadecimal number. If there are no digits, the null character is the | |
232 | separator. Other switches may precede or follow the digits. For | |
f4750dab | 233 | example, if you have a version of I<find> which can print filenames |
f2095865 | 234 | terminated by the null character, you can say this: |
a0d0e21e | 235 | |
19799a22 | 236 | find . -name '*.orig' -print0 | perl -n0e unlink |
a0d0e21e LW |
237 | |
238 | The special value 00 will cause Perl to slurp files in paragraph mode. | |
7ba31cb4 KW |
239 | Any value 0400 or above will cause Perl to slurp files whole, but by convention |
240 | the value 0777 is the one normally used for this purpose. | |
f2095865 | 241 | |
7ba31cb4 | 242 | You can also specify the separator character using hexadecimal notation: |
f4750dab TC |
243 | B<-0xI<HHH...>>, where the C<I<H>> are valid hexadecimal digits. Unlike |
244 | the octal form, this one may be used to specify any Unicode character, even | |
245 | those beyond 0xFF. So if you I<really> want a record separator of 0777, | |
246 | specify it as B<-0x1FF>. (This means that you cannot use the B<-x> option | |
247 | with a directory name that consists of hexadecimal digits, or else Perl | |
248 | will think you have specified a hex number to B<-0>.) | |
a0d0e21e LW |
249 | |
250 | =item B<-a> | |
d74e8afc | 251 | X<-a> X<autosplit> |
a0d0e21e LW |
252 | |
253 | turns on autosplit mode when used with a B<-n> or B<-p>. An implicit | |
254 | split command to the @F array is done as the first thing inside the | |
255 | implicit while loop produced by the B<-n> or B<-p>. | |
256 | ||
257 | perl -ane 'print pop(@F), "\n";' | |
258 | ||
259 | is equivalent to | |
260 | ||
261 | while (<>) { | |
262 | @F = split(' '); | |
263 | print pop(@F), "\n"; | |
264 | } | |
265 | ||
266 | An alternate delimiter may be specified using B<-F>. | |
267 | ||
24ffa309 TC |
268 | B<-a> implicitly sets B<-n>. |
269 | ||
a05d7ebb | 270 | =item B<-C [I<number/list>]> |
d74e8afc | 271 | X<-C> |
46487f74 | 272 | |
f4750dab | 273 | The B<-C> flag controls some of the Perl Unicode features. |
a05d7ebb | 274 | |
f4750dab | 275 | As of 5.8.1, the B<-C> can be followed either by a number or a list |
f3f8427d | 276 | of option letters. The letters, their numeric values, and effects |
8aa8f774 | 277 | are as follows; listing the letters is equal to summing the numbers. |
9f21530f | 278 | |
73e12209 A |
279 | I 1 STDIN is assumed to be in UTF-8 |
280 | O 2 STDOUT will be in UTF-8 | |
281 | E 4 STDERR will be in UTF-8 | |
282 | S 7 I + O + E | |
283 | i 8 UTF-8 is the default PerlIO layer for input streams | |
284 | o 16 UTF-8 is the default PerlIO layer for output streams | |
285 | D 24 i + o | |
286 | A 32 the @ARGV elements are expected to be strings encoded | |
287 | in UTF-8 | |
60b7c710 KW |
288 | L 64 normally the "IOEioA" are unconditional, the L makes |
289 | them conditional on the locale environment variables | |
290 | (the LC_ALL, LC_TYPE, and LANG, in the order of | |
291 | decreasing precedence) -- if the variables indicate | |
73e12209 | 292 | UTF-8, then the selected "IOEioA" are in effect |
60b7c710 KW |
293 | a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching |
294 | code in debugging mode. | |
5a22a2bb NC |
295 | |
296 | =for documenting_the_underdocumented | |
297 | perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */" | |
9f21530f | 298 | |
f23930d5 NC |
299 | =for todo |
300 | perltodo mentions Unicode in %ENV and filenames. I guess that these will be | |
301 | options e and f (or F). | |
302 | ||
f4750dab | 303 | For example, B<-COE> and B<-C6> will both turn on UTF-8-ness on both |
9f21530f JH |
304 | STDOUT and STDERR. Repeating letters is just redundant, not cumulative |
305 | nor toggling. | |
a05d7ebb | 306 | |
44505768 | 307 | The C<io> options mean that any subsequent open() (or similar I/O |
88770b48 NT |
308 | operations) in the current file scope will have the C<:utf8> PerlIO layer |
309 | implicitly applied to them, in other words, UTF-8 is expected from any | |
310 | input stream, and UTF-8 is produced to any output stream. This is just | |
311 | the default, with explicit layers in open() and with binmode() one can | |
312 | manipulate streams as usual. | |
44505768 | 313 | |
f4750dab | 314 | B<-C> on its own (not followed by any number or option list), or the |
47427c4e | 315 | empty string C<""> for the C<PERL_UNICODE> environment variable, has the |
f4750dab TC |
316 | same effect as B<-CSDL>. In other words, the standard I/O handles and |
317 | the default C<open()> layer are UTF-8-fied I<but> only if the locale | |
47427c4e RGS |
318 | environment variables indicate a UTF-8 locale. This behaviour follows |
319 | the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0. | |
370155be | 320 | (See L<perl581delta/UTF-8 no longer default under UTF-8 locales>.) |
a05d7ebb | 321 | |
f4750dab | 322 | You can use B<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly |
5b4f334e | 323 | disable all the above Unicode features. |
fde18df1 | 324 | |
8aa8f774 | 325 | The read-only magic variable C<${^UNICODE}> reflects the numeric value |
f60ef620 | 326 | of this setting. This variable is set during Perl startup and is |
ab9e1bb7 | 327 | thereafter read-only. If you want runtime effects, use the three-arg |
2307c6d0 | 328 | open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>), |
ab9e1bb7 | 329 | and the C<open> pragma (see L<open>). |
fde18df1 | 330 | |
f4750dab | 331 | (In Perls earlier than 5.8.1 the B<-C> switch was a Win32-only switch |
fde18df1 JH |
332 | that enabled the use of Unicode-aware "wide system call" Win32 APIs. |
333 | This feature was practically unused, however, and the command line | |
334 | switch was therefore "recycled".) | |
46487f74 | 335 | |
f4750dab TC |
336 | B<Note:> Since perl 5.10.1, if the B<-C> option is used on the C<#!> line, |
337 | it must be specified on the command line as well, since the standard streams | |
618078e9 | 338 | are already set up at this point in the execution of the perl interpreter. |
4ba71d51 | 339 | You can also use binmode() to set the encoding of an I/O stream. |
618078e9 | 340 | |
a0d0e21e | 341 | =item B<-c> |
d74e8afc | 342 | X<-c> |
a0d0e21e | 343 | |
19799a22 | 344 | causes Perl to check the syntax of the program and then exit without |
f4750dab TC |
345 | executing it. Actually, it I<will> execute and C<BEGIN>, C<UNITCHECK>, |
346 | or C<CHECK> blocks and any C<use> statements: these are considered as | |
347 | occurring outside the execution of your program. C<INIT> and C<END> | |
348 | blocks, however, will be skipped. | |
a0d0e21e LW |
349 | |
350 | =item B<-d> | |
d74e8afc | 351 | X<-d> X<-dt> |
a0d0e21e | 352 | |
2cbb2ee1 RGS |
353 | =item B<-dt> |
354 | ||
19799a22 | 355 | runs the program under the Perl debugger. See L<perldebug>. |
2cbb2ee1 RGS |
356 | If B<t> is specified, it indicates to the debugger that threads |
357 | will be used in the code being debugged. | |
a0d0e21e | 358 | |
f4750dab | 359 | =item B<-d:>I<MOD[=bar,baz]> |
d74e8afc | 360 | X<-d> X<-dt> |
3c81428c | 361 | |
f4750dab | 362 | =item B<-dt:>I<MOD[=bar,baz]> |
2cbb2ee1 | 363 | |
f4750dab TC |
364 | runs the program under the control of a debugging, profiling, or tracing |
365 | module installed as C<Devel::I<MOD>>. E.g., B<-d:DProf> executes the | |
366 | program using the C<Devel::DProf> profiler. As with the B<-M> flag, options | |
367 | may be passed to the C<Devel::I<MOD>> package where they will be received | |
368 | and interpreted by the C<Devel::I<MOD>::import> routine. Again, like B<-M>, | |
369 | use -B<-d:-I<MOD>> to call C<Devel::I<MOD>::unimport> instead of import. The | |
370 | comma-separated list of options must follow a C<=> character. If B<t> is | |
371 | specified, it indicates to the debugger that threads will be used in the | |
372 | code being debugged. See L<perldebug>. | |
3c81428c | 373 | |
db2ba183 | 374 | =item B<-D>I<letters> |
d74e8afc | 375 | X<-D> X<DEBUGGING> X<-DDEBUGGING> |
a0d0e21e | 376 | |
db2ba183 | 377 | =item B<-D>I<number> |
a0d0e21e | 378 | |
19799a22 | 379 | sets debugging flags. To watch how it executes your program, use |
db2ba183 TB |
380 | B<-Dtls>. (This works only if debugging is compiled into your |
381 | Perl.) Another nice value is B<-Dx>, which lists your compiled | |
4197b13f | 382 | syntax tree. And B<-Dr> displays compiled regular expressions; |
44a4342c | 383 | the format of the output is explained in L<perldebguts>. |
4197b13f MJD |
384 | |
385 | As an alternative, specify a number instead of list of letters (e.g., | |
386 | B<-D14> is equivalent to B<-Dtls>): | |
a0d0e21e | 387 | |
9388183f | 388 | 1 p Tokenizing and parsing (with v, displays parse stack) |
3679267a | 389 | 2 s Stack snapshots (with v, displays all stacks) |
db2ba183 TB |
390 | 4 l Context (loop) stack processing |
391 | 8 t Trace execution | |
392 | 16 o Method and overloading resolution | |
393 | 32 c String/numeric conversions | |
4c84d7f2 | 394 | 64 P Print profiling info, source file input state |
d7a2c63c | 395 | 128 m Memory and SV allocation |
db2ba183 TB |
396 | 256 f Format processing |
397 | 512 r Regular expression parsing and execution | |
398 | 1024 x Syntax tree dump | |
399 | 2048 u Tainting checks | |
60b7c710 KW |
400 | 4096 U Unofficial, User hacking (reserved for private, |
401 | unreleased use) | |
db2ba183 TB |
402 | 8192 H Hash dump -- usurps values() |
403 | 16384 X Scratchpad allocation | |
404 | 32768 D Cleaning up | |
56967202 | 405 | 65536 S Op slab allocation |
f4750dab | 406 | 131072 T Tokenizing |
60b7c710 KW |
407 | 262144 R Include reference counts of dumped variables (eg when |
408 | using -Ds) | |
409 | 524288 J show s,t,P-debug (don't Jump over) on opcodes within | |
410 | package DB | |
d6721266 | 411 | 1048576 v Verbose: use in conjunction with other flags |
46187eeb | 412 | 2097152 C Copy On Write |
ecae49c0 | 413 | 4194304 A Consistency checks on internal structures |
60b7c710 KW |
414 | 8388608 q quiet - currently only suppresses the "EXECUTING" |
415 | message | |
d7c0d282 | 416 | 16777216 M trace smart match resolution |
60b7c710 KW |
417 | 33554432 B dump suBroutine definitions, including special Blocks |
418 | like BEGIN | |
a0d0e21e | 419 | |
19799a22 | 420 | All these flags require B<-DDEBUGGING> when you compile the Perl |
c85da6fc TH |
421 | executable (but see C<:opd> in L<Devel::Peek> or L<re/'debug' mode> |
422 | which may change this). | |
44a4342c | 423 | See the F<INSTALL> file in the Perl source distribution |
19799a22 | 424 | for how to do this. This flag is automatically set if you include B<-g> |
8c52afec IZ |
425 | option when C<Configure> asks you about optimizer/debugger flags. |
426 | ||
19799a22 GS |
427 | If you're just trying to get a print out of each line of Perl code |
428 | as it executes, the way that C<sh -x> provides for shell scripts, | |
44a4342c | 429 | you can't use Perl's B<-D> switch. Instead do this |
19799a22 | 430 | |
c406981e | 431 | # If you have "env" utility |
fdac53cd | 432 | env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program |
c406981e | 433 | |
19799a22 GS |
434 | # Bourne shell syntax |
435 | $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program | |
436 | ||
437 | # csh syntax | |
438 | % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program) | |
439 | ||
440 | See L<perldebug> for details and variations. | |
441 | ||
a0d0e21e | 442 | =item B<-e> I<commandline> |
d74e8afc | 443 | X<-e> |
a0d0e21e | 444 | |
19799a22 GS |
445 | may be used to enter one line of program. If B<-e> is given, Perl |
446 | will not look for a filename in the argument list. Multiple B<-e> | |
447 | commands may be given to build up a multi-line script. Make sure | |
448 | to use semicolons where you would in a normal program. | |
a0d0e21e | 449 | |
bc9b29db RH |
450 | =item B<-E> I<commandline> |
451 | X<-E> | |
452 | ||
453 | behaves just like B<-e>, except that it implicitly enables all | |
454 | optional features (in the main compilation unit). See L<feature>. | |
455 | ||
20ef40cf | 456 | =item B<-f> |
174299ac | 457 | X<-f> X<sitecustomize> X<sitecustomize.pl> |
20ef40cf | 458 | |
4a42f219 | 459 | Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup. |
20ef40cf GA |
460 | |
461 | Perl can be built so that it by default will try to execute | |
e846cbe5 | 462 | F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block). |
f4750dab TC |
463 | This is a hook that allows the sysadmin to customize how Perl behaves. |
464 | It can for instance be used to add entries to the @INC array to make Perl | |
e846cbe5 | 465 | find modules in non-standard locations. |
20ef40cf | 466 | |
298ca354 PBB |
467 | Perl actually inserts the following code: |
468 | ||
469 | BEGIN { | |
470 | do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; } | |
471 | && do "$Config{sitelib}/sitecustomize.pl"; | |
472 | } | |
473 | ||
474 | Since it is an actual C<do> (not a C<require>), F<sitecustomize.pl> | |
475 | doesn't need to return a true value. The code is run in package C<main>, | |
476 | in its own lexical scope. However, if the script dies, C<$@> will not | |
477 | be set. | |
478 | ||
479 | The value of C<$Config{sitelib}> is also determined in C code and not | |
480 | read from C<Config.pm>, which is not loaded. | |
481 | ||
f4750dab | 482 | The code is executed I<very> early. For example, any changes made to |
298ca354 PBB |
483 | C<@INC> will show up in the output of `perl -V`. Of course, C<END> |
484 | blocks will be likewise executed very late. | |
485 | ||
486 | To determine at runtime if this capability has been compiled in your | |
487 | perl, you can check the value of C<$Config{usesitecustomize}>. | |
488 | ||
e0ebc809 | 489 | =item B<-F>I<pattern> |
d74e8afc | 490 | X<-F> |
a0d0e21e | 491 | |
24ffa309 TC |
492 | specifies the pattern to split on for B<-a>. The pattern may be |
493 | surrounded by C<//>, C<"">, or C<''>, otherwise it will be put in single | |
494 | quotes. You can't use literal whitespace in the pattern. | |
495 | ||
496 | B<-F> implicitly sets both B<-a> and B<-n>. | |
a0d0e21e | 497 | |
e0ebc809 | 498 | =item B<-h> |
d74e8afc | 499 | X<-h> |
e0ebc809 | 500 | |
501 | prints a summary of the options. | |
502 | ||
503 | =item B<-i>[I<extension>] | |
d74e8afc | 504 | X<-i> X<in-place> |
a0d0e21e | 505 | |
2d259d92 CK |
506 | specifies that files processed by the C<E<lt>E<gt>> construct are to be |
507 | edited in-place. It does this by renaming the input file, opening the | |
508 | output file by the original name, and selecting that output file as the | |
509 | default for print() statements. The extension, if supplied, is used to | |
510 | modify the name of the old file to make a backup copy, following these | |
511 | rules: | |
512 | ||
479e5f87 PM |
513 | If no extension is supplied, and your system supports it, the original |
514 | I<file> is kept open without a name while the output is redirected to | |
515 | a new file with the original I<filename>. When perl exits, cleanly or not, | |
516 | the original I<file> is unlinked. | |
2d259d92 | 517 | |
19799a22 GS |
518 | If the extension doesn't contain a C<*>, then it is appended to the |
519 | end of the current filename as a suffix. If the extension does | |
520 | contain one or more C<*> characters, then each C<*> is replaced | |
521 | with the current filename. In Perl terms, you could think of this | |
522 | as: | |
2d259d92 | 523 | |
66606d78 | 524 | ($backup = $extension) =~ s/\*/$file_name/g; |
2d259d92 CK |
525 | |
526 | This allows you to add a prefix to the backup file, instead of (or in | |
527 | addition to) a suffix: | |
528 | ||
60b7c710 KW |
529 | $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to |
530 | # 'orig_fileA' | |
2d259d92 CK |
531 | |
532 | Or even to place backup copies of the original files into another | |
533 | directory (provided the directory already exists): | |
534 | ||
60b7c710 KW |
535 | $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to |
536 | # 'old/fileA.orig' | |
2d259d92 | 537 | |
66606d78 CK |
538 | These sets of one-liners are equivalent: |
539 | ||
60b7c710 KW |
540 | $ perl -pi -e 's/bar/baz/' fileA # overwrite current file |
541 | $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file | |
66606d78 | 542 | |
60b7c710 KW |
543 | $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' |
544 | $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' | |
66606d78 | 545 | |
2d259d92 | 546 | From the shell, saying |
a0d0e21e | 547 | |
19799a22 | 548 | $ perl -p -i.orig -e "s/foo/bar/; ... " |
a0d0e21e | 549 | |
19799a22 | 550 | is the same as using the program: |
a0d0e21e | 551 | |
19799a22 | 552 | #!/usr/bin/perl -pi.orig |
a0d0e21e LW |
553 | s/foo/bar/; |
554 | ||
555 | which is equivalent to | |
556 | ||
557 | #!/usr/bin/perl | |
19799a22 GS |
558 | $extension = '.orig'; |
559 | LINE: while (<>) { | |
a0d0e21e | 560 | if ($ARGV ne $oldargv) { |
66606d78 CK |
561 | if ($extension !~ /\*/) { |
562 | $backup = $ARGV . $extension; | |
563 | } | |
564 | else { | |
565 | ($backup = $extension) =~ s/\*/$ARGV/g; | |
566 | } | |
567 | rename($ARGV, $backup); | |
a0d0e21e LW |
568 | open(ARGVOUT, ">$ARGV"); |
569 | select(ARGVOUT); | |
570 | $oldargv = $ARGV; | |
571 | } | |
572 | s/foo/bar/; | |
573 | } | |
574 | continue { | |
575 | print; # this prints to original filename | |
576 | } | |
577 | select(STDOUT); | |
578 | ||
579 | except that the B<-i> form doesn't need to compare $ARGV to $oldargv to | |
580 | know when the filename has changed. It does, however, use ARGVOUT for | |
66606d78 CK |
581 | the selected filehandle. Note that STDOUT is restored as the default |
582 | output filehandle after the loop. | |
583 | ||
584 | As shown above, Perl creates the backup file whether or not any output | |
585 | is actually changed. So this is just a fancy way to copy files: | |
586 | ||
cd2d1bac | 587 | $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3... |
19799a22 | 588 | or |
cd2d1bac | 589 | $ perl -p -i'.orig' -e 1 file1 file2 file3... |
66606d78 CK |
590 | |
591 | You can use C<eof> without parentheses to locate the end of each input | |
592 | file, in case you want to append to each file, or reset line numbering | |
593 | (see example in L<perlfunc/eof>). | |
594 | ||
595 | If, for a given file, Perl is unable to create the backup file as | |
596 | specified in the extension then it will skip that file and continue on | |
597 | with the next one (if it exists). | |
598 | ||
1dcc3c19 DG |
599 | For a discussion of issues surrounding file permissions and B<-i>, see |
600 | L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber | |
601 | protected files? Isn't this a bug in Perl?>. | |
66606d78 CK |
602 | |
603 | You cannot use B<-i> to create directories or to strip extensions from | |
604 | files. | |
a0d0e21e | 605 | |
19799a22 GS |
606 | Perl does not expand C<~> in filenames, which is good, since some |
607 | folks use it for their backup files: | |
a0d0e21e | 608 | |
19799a22 GS |
609 | $ perl -pi~ -e 's/foo/bar/' file1 file2 file3... |
610 | ||
a66b22ca | 611 | Note that because B<-i> renames or deletes the original file before |
e1020413 | 612 | creating a new file of the same name, Unix-style soft and hard links will |
0cb0633f | 613 | not be preserved. |
a66b22ca | 614 | |
19799a22 | 615 | Finally, the B<-i> switch does not impede execution when no |
a2008d6d GS |
616 | files are given on the command line. In this case, no backup is made |
617 | (the original file cannot, of course, be determined) and processing | |
618 | proceeds from STDIN to STDOUT as might be expected. | |
619 | ||
a0d0e21e | 620 | =item B<-I>I<directory> |
d74e8afc | 621 | X<-I> X<@INC> |
a0d0e21e | 622 | |
e0ebc809 | 623 | Directories specified by B<-I> are prepended to the search path for |
4c84d7f2 | 624 | modules (C<@INC>). |
a0d0e21e | 625 | |
e0ebc809 | 626 | =item B<-l>[I<octnum>] |
d74e8afc | 627 | X<-l> X<$/> X<$\> |
a0d0e21e | 628 | |
19799a22 GS |
629 | enables automatic line-ending processing. It has two separate |
630 | effects. First, it automatically chomps C<$/> (the input record | |
631 | separator) when used with B<-n> or B<-p>. Second, it assigns C<$\> | |
632 | (the output record separator) to have the value of I<octnum> so | |
633 | that any print statements will have that separator added back on. | |
634 | If I<octnum> is omitted, sets C<$\> to the current value of | |
635 | C<$/>. For instance, to trim lines to 80 columns: | |
a0d0e21e LW |
636 | |
637 | perl -lpe 'substr($_, 80) = ""' | |
638 | ||
639 | Note that the assignment C<$\ = $/> is done when the switch is processed, | |
640 | so the input record separator can be different than the output record | |
641 | separator if the B<-l> switch is followed by a B<-0> switch: | |
642 | ||
643 | gnufind / -print0 | perl -ln0e 'print "found $_" if -p' | |
644 | ||
1fef88e7 | 645 | This sets C<$\> to newline and then sets C<$/> to the null character. |
a0d0e21e | 646 | |
e0ebc809 | 647 | =item B<-m>[B<->]I<module> |
d74e8afc | 648 | X<-m> X<-M> |
e0ebc809 | 649 | |
650 | =item B<-M>[B<->]I<module> | |
c07a80fd | 651 | |
e0ebc809 | 652 | =item B<-M>[B<->]I<'module ...'> |
653 | ||
654 | =item B<-[mM]>[B<->]I<module=arg[,arg]...> | |
3c81428c | 655 | |
19799a22 GS |
656 | B<-m>I<module> executes C<use> I<module> C<();> before executing your |
657 | program. | |
3c81428c | 658 | |
19799a22 GS |
659 | B<-M>I<module> executes C<use> I<module> C<;> before executing your |
660 | program. You can use quotes to add extra code after the module name, | |
f4750dab | 661 | e.g., C<'-MI<MODULE> qw(foo bar)'>. |
3c81428c | 662 | |
f4750dab | 663 | If the first character after the B<-M> or B<-m> is a dash (B<->) |
a5f75d66 AD |
664 | then the 'use' is replaced with 'no'. |
665 | ||
54310121 | 666 | A little builtin syntactic sugar means you can also say |
f4750dab TC |
667 | B<-mI<MODULE>=foo,bar> or B<-MI<MODULE>=foo,bar> as a shortcut for |
668 | B<'-MI<MODULE> qw(foo bar)'>. This avoids the need to use quotes when | |
669 | importing symbols. The actual code generated by B<-MI<MODULE>=foo,bar> is | |
e0ebc809 | 670 | C<use module split(/,/,q{foo,bar})>. Note that the C<=> form |
19799a22 | 671 | removes the distinction between B<-m> and B<-M>. |
3c81428c | 672 | |
f4750dab TC |
673 | A consequence of this is that B<-MI<MODULE>=number> never does a version check, |
674 | unless C<I<MODULE>::import()> itself is set up to do a version check, which | |
675 | could happen for example if I<MODULE> inherits from L<Exporter>. | |
642d0c2f | 676 | |
a0d0e21e | 677 | =item B<-n> |
d74e8afc | 678 | X<-n> |
a0d0e21e | 679 | |
19799a22 | 680 | causes Perl to assume the following loop around your program, which |
f4750dab TC |
681 | makes it iterate over filename arguments somewhat like I<sed -n> or |
682 | I<awk>: | |
a0d0e21e | 683 | |
19799a22 | 684 | LINE: |
a0d0e21e | 685 | while (<>) { |
19799a22 | 686 | ... # your program goes here |
a0d0e21e LW |
687 | } |
688 | ||
76c9ab0e | 689 | Note that the lines are not printed by default. See L</-p> to have |
08e9d68e | 690 | lines printed. If a file named by an argument cannot be opened for |
19799a22 | 691 | some reason, Perl warns you about it and moves on to the next file. |
08e9d68e | 692 | |
48ab5743 ML |
693 | Also note that C<< <> >> passes command line arguments to |
694 | L<perlfunc/open>, which doesn't necessarily interpret them as file names. | |
695 | See L<perlop> for possible security implications. | |
696 | ||
fa11829f | 697 | Here is an efficient way to delete all files that haven't been modified for |
9976c5c7 | 698 | at least a week: |
a0d0e21e | 699 | |
19799a22 | 700 | find . -mtime +7 -print | perl -nle unlink |
a0d0e21e | 701 | |
f4750dab | 702 | This is faster than using the B<-exec> switch of I<find> because you don't |
19799a22 GS |
703 | have to start a process on every filename found. It does suffer from |
704 | the bug of mishandling newlines in pathnames, which you can fix if | |
44a4342c | 705 | you follow the example under B<-0>. |
a0d0e21e LW |
706 | |
707 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
f4750dab | 708 | the implicit program loop, just as in I<awk>. |
a0d0e21e LW |
709 | |
710 | =item B<-p> | |
d74e8afc | 711 | X<-p> |
a0d0e21e | 712 | |
19799a22 | 713 | causes Perl to assume the following loop around your program, which |
f4750dab | 714 | makes it iterate over filename arguments somewhat like I<sed>: |
a0d0e21e LW |
715 | |
716 | ||
19799a22 | 717 | LINE: |
a0d0e21e | 718 | while (<>) { |
19799a22 | 719 | ... # your program goes here |
a0d0e21e | 720 | } continue { |
08e9d68e | 721 | print or die "-p destination: $!\n"; |
a0d0e21e LW |
722 | } |
723 | ||
08e9d68e DD |
724 | If a file named by an argument cannot be opened for some reason, Perl |
725 | warns you about it, and moves on to the next file. Note that the | |
c2611fb3 | 726 | lines are printed automatically. An error occurring during printing is |
08e9d68e DD |
727 | treated as fatal. To suppress printing use the B<-n> switch. A B<-p> |
728 | overrides a B<-n> switch. | |
a0d0e21e LW |
729 | |
730 | C<BEGIN> and C<END> blocks may be used to capture control before or after | |
f4750dab | 731 | the implicit loop, just as in I<awk>. |
a0d0e21e | 732 | |
a0d0e21e | 733 | =item B<-s> |
d74e8afc | 734 | X<-s> |
a0d0e21e | 735 | |
19799a22 GS |
736 | enables rudimentary switch parsing for switches on the command |
737 | line after the program name but before any filename arguments (or before | |
74ac850a | 738 | an argument of B<-->). Any switch found there is removed from @ARGV and sets the |
19799a22 | 739 | corresponding variable in the Perl program. The following program |
3c0facb2 GS |
740 | prints "1" if the program is invoked with a B<-xyz> switch, and "abc" |
741 | if it is invoked with B<-xyz=abc>. | |
a0d0e21e LW |
742 | |
743 | #!/usr/bin/perl -s | |
3c0facb2 | 744 | if ($xyz) { print "$xyz\n" } |
a0d0e21e | 745 | |
1dcc3c19 DG |
746 | Do note that a switch like B<--help> creates the variable C<${-help}>, which is |
747 | not compliant with C<use strict "refs">. Also, when using this option on a | |
748 | script with warnings enabled you may get a lot of spurious "used only once" | |
749 | warnings. | |
3bbcc830 | 750 | |
a0d0e21e | 751 | =item B<-S> |
d74e8afc | 752 | X<-S> |
a0d0e21e LW |
753 | |
754 | makes Perl use the PATH environment variable to search for the | |
f4750dab | 755 | program unless the name of the program contains path separators. |
19799a22 | 756 | |
2a92aaa0 GS |
757 | On some platforms, this also makes Perl append suffixes to the |
758 | filename while searching for it. For example, on Win32 platforms, | |
759 | the ".bat" and ".cmd" suffixes are appended if a lookup for the | |
760 | original name fails, and if the name does not already end in one | |
f4750dab TC |
761 | of those suffixes. If your Perl was compiled with C<DEBUGGING> turned |
762 | on, using the B<-Dp> switch to Perl shows how the search progresses. | |
2a92aaa0 | 763 | |
f4750dab TC |
764 | Typically this is used to emulate C<#!> startup on platforms that don't |
765 | support C<#!>. It's also convenient when debugging a script that uses C<#!>, | |
fa3aa65a JC |
766 | and is thus normally found by the shell's $PATH search mechanism. |
767 | ||
768 | This example works on many platforms that have a shell compatible with | |
769 | Bourne shell: | |
a0d0e21e LW |
770 | |
771 | #!/usr/bin/perl | |
a3cb178b | 772 | eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}' |
a0d0e21e LW |
773 | if $running_under_some_shell; |
774 | ||
19799a22 GS |
775 | The system ignores the first line and feeds the program to F</bin/sh>, |
776 | which proceeds to try to execute the Perl program as a shell script. | |
a0d0e21e LW |
777 | The shell executes the second line as a normal shell command, and thus |
778 | starts up the Perl interpreter. On some systems $0 doesn't always | |
779 | contain the full pathname, so the B<-S> tells Perl to search for the | |
19799a22 | 780 | program if necessary. After Perl locates the program, it parses the |
a0d0e21e | 781 | lines and ignores them because the variable $running_under_some_shell |
19799a22 | 782 | is never true. If the program will be interpreted by csh, you will need |
a3cb178b | 783 | to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand |
f4750dab TC |
784 | embedded spaces (and such) in the argument list. To start up I<sh> rather |
785 | than I<csh>, some systems may have to replace the C<#!> line with a line | |
a0d0e21e LW |
786 | containing just a colon, which will be politely ignored by Perl. Other |
787 | systems can't control that, and need a totally devious construct that | |
f4750dab | 788 | will work under any of I<csh>, I<sh>, or Perl, such as the following: |
a0d0e21e | 789 | |
19799a22 | 790 | eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}' |
a3cb178b | 791 | & eval 'exec /usr/bin/perl -wS $0 $argv:q' |
5f05dabc | 792 | if $running_under_some_shell; |
a0d0e21e | 793 | |
f4750dab | 794 | If the filename supplied contains directory separators (and so is an |
19799a22 GS |
795 | absolute or relative pathname), and if that file is not found, |
796 | platforms that append file extensions will do so and try to look | |
797 | for the file with those extensions added, one by one. | |
798 | ||
799 | On DOS-like platforms, if the program does not contain directory | |
800 | separators, it will first be searched for in the current directory | |
801 | before being searched for on the PATH. On Unix platforms, the | |
802 | program will be searched for strictly on the PATH. | |
803 | ||
6537fe72 | 804 | =item B<-t> |
d74e8afc | 805 | X<-t> |
6537fe72 MS |
806 | |
807 | Like B<-T>, but taint checks will issue warnings rather than fatal | |
f4750dab | 808 | errors. These warnings can now be controlled normally with C<no warnings |
317ea90d | 809 | qw(taint)>. |
1dbad523 | 810 | |
f4750dab TC |
811 | B<Note: This is not a substitute for C<-T>!> This is meant to be |
812 | used I<only> as a temporary development aid while securing legacy code: | |
813 | for real production code and for new secure code written from scratch, | |
1dbad523 | 814 | always use the real B<-T>. |
6537fe72 | 815 | |
a0d0e21e | 816 | =item B<-T> |
d74e8afc | 817 | X<-T> |
a0d0e21e | 818 | |
f4750dab | 819 | turns on "taint" so you can test them. Ordinarily |
19799a22 GS |
820 | these checks are done only when running setuid or setgid. It's a |
821 | good idea to turn them on explicitly for programs that run on behalf | |
822 | of someone else whom you might not necessarily trust, such as CGI | |
823 | programs or any internet servers you might write in Perl. See | |
824 | L<perlsec> for details. For security reasons, this option must be | |
825 | seen by Perl quite early; usually this means it must appear early | |
f4750dab | 826 | on the command line or in the C<#!> line for systems which support |
19799a22 | 827 | that construct. |
a0d0e21e LW |
828 | |
829 | =item B<-u> | |
d74e8afc | 830 | X<-u> |
a0d0e21e | 831 | |
f4750dab | 832 | This switch causes Perl to dump core after compiling your |
19799a22 | 833 | program. You can then in theory take this core dump and turn it |
f4750dab | 834 | into an executable file by using the I<undump> program (not supplied). |
19799a22 GS |
835 | This speeds startup at the expense of some disk space (which you |
836 | can minimize by stripping the executable). (Still, a "hello world" | |
837 | executable comes out to about 200K on my machine.) If you want to | |
838 | execute a portion of your program before dumping, use the dump() | |
f4750dab | 839 | operator instead. Note: availability of I<undump> is platform |
19799a22 GS |
840 | specific and may not be available for a specific port of Perl. |
841 | ||
a0d0e21e | 842 | =item B<-U> |
d74e8afc | 843 | X<-U> |
a0d0e21e LW |
844 | |
845 | allows Perl to do unsafe operations. Currently the only "unsafe" | |
f4750dab TC |
846 | operations are attempting to unlink directories while running as superuser |
847 | and running setuid programs with fatal taint checks turned into warnings. | |
848 | Note that warnings must be enabled along with this option to actually | |
849 | I<generate> the taint-check warnings. | |
a0d0e21e LW |
850 | |
851 | =item B<-v> | |
d74e8afc | 852 | X<-v> |
a0d0e21e | 853 | |
19799a22 | 854 | prints the version and patchlevel of your perl executable. |
a0d0e21e | 855 | |
3c81428c | 856 | =item B<-V> |
d74e8afc | 857 | X<-V> |
3c81428c | 858 | |
859 | prints summary of the major perl configuration values and the current | |
19799a22 | 860 | values of @INC. |
3c81428c | 861 | |
307dc113 | 862 | =item B<-V:>I<configvar> |
3c81428c | 863 | |
4a305f6a | 864 | Prints to STDOUT the value of the named configuration variable(s), |
f4750dab | 865 | with multiples when your C<I<configvar>> argument looks like a regex (has |
307dc113 | 866 | non-letters). For example: |
3c81428c | 867 | |
307dc113 JC |
868 | $ perl -V:libc |
869 | libc='/lib/libc-2.2.4.so'; | |
4a305f6a JC |
870 | $ perl -V:lib. |
871 | libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc'; | |
872 | libc='/lib/libc-2.2.4.so'; | |
873 | $ perl -V:lib.* | |
874 | libpth='/usr/local/lib /lib /usr/lib'; | |
875 | libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc'; | |
876 | lib_ext='.a'; | |
877 | libc='/lib/libc-2.2.4.so'; | |
878 | libperl='libperl.a'; | |
879 | .... | |
880 | ||
881 | Additionally, extra colons can be used to control formatting. A | |
f4750dab | 882 | trailing colon suppresses the linefeed and terminator ";", allowing |
4a305f6a | 883 | you to embed queries into shell commands. (mnemonic: PATH separator |
f4750dab | 884 | ":".) |
4a305f6a JC |
885 | |
886 | $ echo "compression-vars: " `perl -V:z.*: ` " are here !" | |
887 | compression-vars: zcat='' zip='zip' are here ! | |
888 | ||
f4750dab | 889 | A leading colon removes the "name=" part of the response, this allows |
307dc113 | 890 | you to map to the name you need. (mnemonic: empty label) |
4a305f6a JC |
891 | |
892 | $ echo "goodvfork="`./perl -Ilib -V::usevfork` | |
893 | goodvfork=false; | |
894 | ||
895 | Leading and trailing colons can be used together if you need | |
896 | positional parameter values without the names. Note that in the case | |
f4750dab | 897 | below, the C<PERL_API> params are returned in alphabetical order. |
4a305f6a JC |
898 | |
899 | $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now | |
900 | building_on 'linux' '5' '1' '9' now | |
a0d0e21e | 901 | |
19799a22 | 902 | =item B<-w> |
d74e8afc | 903 | X<-w> |
774d564b | 904 | |
19799a22 | 905 | prints warnings about dubious constructs, such as variable names |
f4750dab TC |
906 | mentioned only once and scalar variables used |
907 | before being set; redefined subroutines; references to undefined | |
908 | filehandles; filehandles opened read-only that you are attempting | |
909 | to write on; values used as a number that don't I<look> like numbers; | |
910 | using an array as though it were a scalar; if your subroutines | |
911 | recurse more than 100 deep; and innumerable other things. | |
912 | ||
913 | This switch really just enables the global C<$^W> variable; normally, | |
914 | the lexically scoped C<use warnings> pragma is preferred. You | |
19799a22 GS |
915 | can disable or promote into fatal errors specific warnings using |
916 | C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>. | |
f4750dab | 917 | See also L<perldiag> and L<perltrap>. A fine-grained warning |
19799a22 | 918 | facility is also available if you want to manipulate entire classes |
9f1b1f2d | 919 | of warnings; see L<warnings> or L<perllexwarn>. |
a0d0e21e | 920 | |
0453d815 | 921 | =item B<-W> |
d74e8afc | 922 | X<-W> |
0453d815 | 923 | |
3c0facb2 | 924 | Enables all warnings regardless of C<no warnings> or C<$^W>. |
0453d815 PM |
925 | See L<perllexwarn>. |
926 | ||
927 | =item B<-X> | |
d74e8afc | 928 | X<-X> |
0453d815 | 929 | |
3c0facb2 | 930 | Disables all warnings regardless of C<use warnings> or C<$^W>. |
0453d815 PM |
931 | See L<perllexwarn>. |
932 | ||
136e4fd6 | 933 | =item B<-x> |
d74e8afc | 934 | X<-x> |
136e4fd6 | 935 | |
d3bf4b0e | 936 | =item B<-x>I<directory> |
a0d0e21e | 937 | |
19799a22 | 938 | tells Perl that the program is embedded in a larger chunk of unrelated |
f4750dab TC |
939 | text, such as in a mail message. Leading garbage will be |
940 | discarded until the first line that starts with C<#!> and contains the | |
19799a22 | 941 | string "perl". Any meaningful switches on that line will be applied. |
3d6c2ba7 B |
942 | |
943 | All references to line numbers by the program (warnings, errors, ...) | |
f4750dab TC |
944 | will treat the C<#!> line as the first line. |
945 | Thus a warning on the 2nd line of the program, which is on the 100th | |
946 | line in the file will be reported as line 2, not as line 100. | |
947 | This can be overridden by using the C<#line> directive. | |
96090e4f | 948 | (See L<perlsyn/"Plain Old Comments (Not!)">) |
3d6c2ba7 | 949 | |
19799a22 GS |
950 | If a directory name is specified, Perl will switch to that directory |
951 | before running the program. The B<-x> switch controls only the | |
952 | disposal of leading garbage. The program must be terminated with | |
f4750dab TC |
953 | C<__END__> if there is trailing garbage to be ignored; the program |
954 | can process any or all of the trailing garbage via the C<DATA> filehandle | |
955 | if desired. | |
a0d0e21e | 956 | |
353c6505 | 957 | The directory, if specified, must appear immediately following the B<-x> |
d3bf4b0e DN |
958 | with no intervening whitespace. |
959 | ||
1e422769 | 960 | =back |
961 | ||
962 | =head1 ENVIRONMENT | |
d74e8afc | 963 | X<perl, environment variables> |
1e422769 | 964 | |
965 | =over 12 | |
966 | ||
967 | =item HOME | |
d74e8afc | 968 | X<HOME> |
1e422769 | 969 | |
f4750dab | 970 | Used if C<chdir> has no argument. |
1e422769 | 971 | |
972 | =item LOGDIR | |
d74e8afc | 973 | X<LOGDIR> |
1e422769 | 974 | |
f4750dab | 975 | Used if C<chdir> has no argument and HOME is not set. |
1e422769 | 976 | |
977 | =item PATH | |
d74e8afc | 978 | X<PATH> |
1e422769 | 979 | |
19799a22 | 980 | Used in executing subprocesses, and in finding the program if B<-S> is |
1e422769 | 981 | used. |
982 | ||
983 | =item PERL5LIB | |
d74e8afc | 984 | X<PERL5LIB> |
1e422769 | 985 | |
48b971ca | 986 | A list of directories in which to look for Perl library |
1e422769 | 987 | files before looking in the standard library and the current |
4b85e17e AD |
988 | directory. Any architecture-specific and version-specific directories, |
989 | such as F<version/archname/>, F<version/>, or F<archname/> under the | |
990 | specified locations are automatically included if they exist, with this | |
991 | lookup done at interpreter startup time. In addition, any directories | |
992 | matching the entries in C<$Config{inc_version_list}> are added. | |
993 | (These typically would be for older compatible perl versions installed | |
994 | in the same directory tree.) | |
69681433 A |
995 | |
996 | If PERL5LIB is not defined, PERLLIB is used. Directories are separated | |
e1020413 | 997 | (like in PATH) by a colon on Unixish platforms and by a semicolon on |
69681433 | 998 | Windows (the proper path separator being given by the command C<perl |
f4750dab | 999 | -V:I<path_sep>>). |
951ba7fe | 1000 | |
f4750dab TC |
1001 | When running taint checks, either because the program was running setuid or |
1002 | setgid, or the B<-T> or B<-t> switch was specified, neither PERL5LIB nor | |
1003 | PERLLIB is consulted. The program should instead say: | |
1e422769 | 1004 | |
1005 | use lib "/my/directory"; | |
1006 | ||
54310121 | 1007 | =item PERL5OPT |
d74e8afc | 1008 | X<PERL5OPT> |
54310121 | 1009 | |
f4750dab | 1010 | Command-line options (switches). Switches in this variable are treated |
2b622f1a | 1011 | as if they were on every Perl command line. Only the B<-[CDIMUdmtwW]> |
f4750dab TC |
1012 | switches are allowed. When running taint checks (either because the |
1013 | program was running setuid or setgid, or because the B<-T> or B<-t> | |
1014 | switch was used), this variable is ignored. If PERL5OPT begins with | |
cce9fd8c | 1015 | B<-T>, tainting will be enabled and subsequent options ignored. If |
f4750dab TC |
1016 | PERL5OPT begins with B<-t>, tainting will be enabled, a writable dot |
1017 | removed from @INC, and subsequent options honored. | |
54310121 | 1018 | |
16537909 | 1019 | =item PERLIO |
d74e8afc | 1020 | X<PERLIO> |
16537909 | 1021 | |
44a4342c | 1022 | A space (or colon) separated list of PerlIO layers. If perl is built |
f4750dab | 1023 | to use PerlIO system for IO (the default) these layers affect Perl's IO. |
44a4342c | 1024 | |
f4750dab TC |
1025 | It is conventional to start layer names with a colon (for example, C<:perlio>) to |
1026 | emphasize their similarity to variable "attributes". But the code that parses | |
cce9fd8c | 1027 | layer specification strings, which is also used to decode the PERLIO |
f4750dab | 1028 | environment variable, treats the colon as a separator. |
44a4342c | 1029 | |
5b64f2bf | 1030 | An unset or empty PERLIO is equivalent to the default set of layers for |
f4750dab | 1031 | your platform; for example, C<:unix:perlio> on Unix-like systems |
1f070127 | 1032 | and C<:unix:crlf> on Windows and other DOS-like systems. |
3b0db4f9 | 1033 | |
f4750dab TC |
1034 | The list becomes the default for I<all> Perl's IO. Consequently only built-in |
1035 | layers can appear in this list, as external layers (such as C<:encoding()>) need | |
cce9fd8c | 1036 | IO in order to load them! See L<"open pragma"|open> for how to add external |
44a4342c NIS |
1037 | encodings as defaults. |
1038 | ||
f4750dab TC |
1039 | Layers it makes sense to include in the PERLIO environment |
1040 | variable are briefly summarized below. For more details see L<PerlIO>. | |
16537909 JH |
1041 | |
1042 | =over 8 | |
1043 | ||
1044 | =item :bytes | |
d74e8afc | 1045 | X<:bytes> |
16537909 | 1046 | |
f4750dab TC |
1047 | A pseudolayer that turns the C<:utf8> flag I<off> for the layer below; |
1048 | unlikely to be useful on its own in the global PERLIO environment variable. | |
18aba96f | 1049 | You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>. |
16537909 JH |
1050 | |
1051 | =item :crlf | |
d74e8afc | 1052 | X<:crlf> |
16537909 | 1053 | |
f4750dab | 1054 | A layer which does CRLF to C<"\n"> translation distinguishing "text" and |
3d897973 IT |
1055 | "binary" files in the manner of MS-DOS and similar operating systems. |
1056 | (It currently does I<not> mimic MS-DOS as far as treating of Control-Z | |
1057 | as being an end-of-file marker.) | |
44a4342c NIS |
1058 | |
1059 | =item :mmap | |
d74e8afc | 1060 | X<:mmap> |
44a4342c | 1061 | |
f4750dab TC |
1062 | A layer that implements "reading" of files by using I<mmap>(2) to |
1063 | make an entire file appear in the process's address space, and then | |
3d897973 | 1064 | using that as PerlIO's "buffer". |
16537909 | 1065 | |
44a4342c | 1066 | =item :perlio |
d74e8afc | 1067 | X<:perlio> |
16537909 | 1068 | |
f4750dab TC |
1069 | This is a re-implementation of stdio-like buffering written as a |
1070 | PerlIO layer. As such it will call whatever layer is below it for | |
1071 | its operations, typically C<:unix>. | |
16537909 | 1072 | |
18aba96f | 1073 | =item :pop |
d74e8afc | 1074 | X<:pop> |
18aba96f JH |
1075 | |
1076 | An experimental pseudolayer that removes the topmost layer. | |
f4750dab | 1077 | Use with the same care as is reserved for nitroglycerine. |
18aba96f | 1078 | |
44a4342c | 1079 | =item :raw |
d74e8afc | 1080 | X<:raw> |
16537909 | 1081 | |
136e4fd6 | 1082 | A pseudolayer that manipulates other layers. Applying the C<:raw> |
18aba96f | 1083 | layer is equivalent to calling C<binmode($fh)>. It makes the stream |
f4750dab TC |
1084 | pass each byte as-is without translation. In particular, both CRLF |
1085 | translation and intuiting C<:utf8> from the locale are disabled. | |
1cbfc93d | 1086 | |
f4750dab TC |
1087 | Unlike in earlier versions of Perl, C<:raw> is I<not> |
1088 | just the inverse of C<:crlf>: other layers which would affect the | |
3d897973 | 1089 | binary nature of the stream are also removed or disabled. |
16537909 | 1090 | |
44a4342c | 1091 | =item :stdio |
d74e8afc | 1092 | X<:stdio> |
44a4342c | 1093 | |
f4750dab | 1094 | This layer provides a PerlIO interface by wrapping system's ANSI C "stdio" |
44a4342c | 1095 | library calls. The layer provides both buffering and IO. |
f4750dab TC |
1096 | Note that the C<:stdio> layer does I<not> do CRLF translation even if that |
1097 | is the platform's normal behaviour. You will need a C<:crlf> layer above it | |
44a4342c NIS |
1098 | to do that. |
1099 | ||
1100 | =item :unix | |
d74e8afc | 1101 | X<:unix> |
44a4342c | 1102 | |
f4750dab | 1103 | Low-level layer that calls C<read>, C<write>, C<lseek>, etc. |
16537909 JH |
1104 | |
1105 | =item :utf8 | |
d74e8afc | 1106 | X<:utf8> |
16537909 | 1107 | |
f4750dab | 1108 | A pseudolayer that enables a flag in the layer below to tell Perl |
3d897973 | 1109 | that output should be in utf8 and that input should be regarded as |
f4750dab TC |
1110 | already in valid utf8 form. B<WARNING: It does not check for validity and as such |
1111 | should be handled with extreme caution for input, because security violations | |
1112 | can occur with non-shortest UTF-8 encodings, etc.> Generally C<:encoding(utf8)> is | |
740d4bb2 | 1113 | the best option when reading UTF-8 encoded data. |
44a4342c NIS |
1114 | |
1115 | =item :win32 | |
d74e8afc | 1116 | X<:win32> |
44a4342c | 1117 | |
ab4f7683 | 1118 | On Win32 platforms this I<experimental> layer uses native "handle" IO |
f4750dab TC |
1119 | rather than a Unix-like numeric file descriptor layer. Known to be |
1120 | buggy in this release (5.14). | |
16537909 JH |
1121 | |
1122 | =back | |
1123 | ||
f4750dab | 1124 | The default set of layers should give acceptable results on all platforms |
44a4342c | 1125 | |
f4750dab TC |
1126 | For Unix platforms that will be the equivalent of "unix perlio" or "stdio". |
1127 | Configure is set up to prefer the "stdio" implementation if the system's library | |
1128 | provides for fast access to the buffer; otherwise, it uses the "unix perlio" | |
44a4342c NIS |
1129 | implementation. |
1130 | ||
f4750dab TC |
1131 | On Win32 the default in this release (5.14) is "unix crlf". Win32's "stdio" |
1132 | has a number of bugs/mis-features for Perl IO which are somewhat depending | |
1133 | on the version and vendor of the C compiler. Using our own C<crlf> layer as | |
1134 | the buffer avoids those issues and makes things more uniform. The C<crlf> | |
1135 | layer provides CRLF conversion as well as buffering. | |
44a4342c | 1136 | |
f4750dab TC |
1137 | This release (5.14) uses C<unix> as the bottom layer on Win32, and so still |
1138 | uses the C compiler's numeric file descriptor routines. There is an | |
1139 | experimental native C<win32> layer, which is expected to be enhanced and | |
1140 | should eventually become the default under Win32. | |
44a4342c | 1141 | |
f4750dab | 1142 | The PERLIO environment variable is completely ignored when Perl |
5437faeb PF |
1143 | is run in taint mode. |
1144 | ||
44a4342c | 1145 | =item PERLIO_DEBUG |
d74e8afc | 1146 | X<PERLIO_DEBUG> |
44a4342c | 1147 | |
f4750dab | 1148 | If set to the name of a file or device, certain operations of PerlIO |
cce9fd8c | 1149 | subsystem will be logged to that file, which is opened in append mode. |
f4750dab | 1150 | Typical uses are in Unix: |
44a4342c | 1151 | |
f4750dab | 1152 | % env PERLIO_DEBUG=/dev/tty perl script ... |
44a4342c | 1153 | |
f4750dab | 1154 | and under Win32, the approximately equivalent: |
44a4342c | 1155 | |
f4750dab | 1156 | > set PERLIO_DEBUG=CON |
44a4342c NIS |
1157 | perl script ... |
1158 | ||
923e8b21 RGS |
1159 | This functionality is disabled for setuid scripts and for scripts run |
1160 | with B<-T>. | |
16537909 | 1161 | |
1e422769 | 1162 | =item PERLLIB |
d74e8afc | 1163 | X<PERLLIB> |
1e422769 | 1164 | |
48b971ca | 1165 | A list of directories in which to look for Perl library |
1e422769 | 1166 | files before looking in the standard library and the current directory. |
1167 | If PERL5LIB is defined, PERLLIB is not used. | |
1168 | ||
f4750dab | 1169 | The PERLLIB environment variable is completely ignored when Perl |
5437faeb PF |
1170 | is run in taint mode. |
1171 | ||
1e422769 | 1172 | =item PERL5DB |
d74e8afc | 1173 | X<PERL5DB> |
1e422769 | 1174 | |
1175 | The command used to load the debugger code. The default is: | |
1176 | ||
f4750dab | 1177 | BEGIN { require "perl5db.pl" } |
1e422769 | 1178 | |
f4750dab | 1179 | The PERL5DB environment variable is only used when Perl is started with |
5437faeb PF |
1180 | a bare B<-d> switch. |
1181 | ||
2cbb2ee1 | 1182 | =item PERL5DB_THREADED |
d74e8afc | 1183 | X<PERL5DB_THREADED> |
2cbb2ee1 RGS |
1184 | |
1185 | If set to a true value, indicates to the debugger that the code being | |
1186 | debugged uses threads. | |
1187 | ||
19799a22 | 1188 | =item PERL5SHELL (specific to the Win32 port) |
d74e8afc | 1189 | X<PERL5SHELL> |
174c211a | 1190 | |
f4750dab TC |
1191 | On Win32 ports only, may be set to an alternative shell that Perl must use |
1192 | internally for executing "backtick" commands or system(). Default is | |
1193 | C<cmd.exe /x/d/c> on WindowsNT and C<command.com /c> on Windows95. The | |
1194 | value is considered space-separated. Precede any character that | |
1195 | needs to be protected, like a space or backslash, with another backslash. | |
ce1da67e GS |
1196 | |
1197 | Note that Perl doesn't use COMSPEC for this purpose because | |
1198 | COMSPEC has a high degree of variability among users, leading to | |
f4750dab | 1199 | portability concerns. Besides, Perl can use a shell that may not be |
ce1da67e GS |
1200 | fit for interactive use, and setting COMSPEC to such a shell may |
1201 | interfere with the proper functioning of other programs (which usually | |
1202 | look in COMSPEC to find a shell fit for interactive use). | |
174c211a | 1203 | |
5437faeb PF |
1204 | Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked |
1205 | when running external commands. It is recommended that | |
1206 | you explicitly set (or delete) C<$ENV{PERL5SHELL}> when running | |
1207 | in taint mode under Windows. | |
1208 | ||
1c972609 | 1209 | =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port) |
d74e8afc | 1210 | X<PERL_ALLOW_NON_IFS_LSP> |
1c972609 | 1211 | |
f4750dab | 1212 | Set to 1 to allow the use of non-IFS compatible LSPs (Layered Service Providers). |
1c972609 SH |
1213 | Perl normally searches for an IFS-compatible LSP because this is required |
1214 | for its emulation of Windows sockets as real filehandles. However, this may | |
f4750dab TC |
1215 | cause problems if you have a firewall such as I<McAfee Guardian>, which requires |
1216 | that all applications use its LSP but which is not IFS-compatible, because clearly | |
1c972609 | 1217 | Perl will normally avoid using such an LSP. |
f4750dab | 1218 | |
1c972609 | 1219 | Setting this environment variable to 1 means that Perl will simply use the |
f4750dab TC |
1220 | first suitable LSP enumerated in the catalog, which keeps I<McAfee Guardian> |
1221 | happy--and in that particular case Perl still works too because I<McAfee | |
1222 | Guardian>'s LSP actually plays other games which allow applications | |
1223 | requiring IFS compatibility to work. | |
1c972609 | 1224 | |
1e422769 | 1225 | =item PERL_DEBUG_MSTATS |
d74e8afc | 1226 | X<PERL_DEBUG_MSTATS> |
1e422769 | 1227 | |
f4750dab TC |
1228 | Relevant only if Perl is compiled with the C<malloc> included with the Perl |
1229 | distribution; that is, if C<perl -V:d_mymalloc> is "define". | |
1230 | ||
1231 | If set, this dumps out memory statistics after execution. If set | |
1232 | to an integer greater than one, also dumps out memory statistics | |
1e422769 | 1233 | after compilation. |
1234 | ||
1235 | =item PERL_DESTRUCT_LEVEL | |
d74e8afc | 1236 | X<PERL_DESTRUCT_LEVEL> |
1e422769 | 1237 | |
f4750dab TC |
1238 | Relevant only if your Perl executable was built with B<-DDEBUGGING>, |
1239 | this controls the behaviour of global destruction of objects and other | |
96090e4f | 1240 | references. See L<perlhacktips/PERL_DESTRUCT_LEVEL> for more information. |
a0d0e21e | 1241 | |
02c7413a | 1242 | =item PERL_DL_NONLAZY |
d74e8afc | 1243 | X<PERL_DL_NONLAZY> |
02c7413a | 1244 | |
f4750dab | 1245 | Set to C<"1"> to have Perl resolve I<all> undefined symbols when it loads |
02c7413a GA |
1246 | a dynamic library. The default behaviour is to resolve symbols when |
1247 | they are used. Setting this variable is useful during testing of | |
f4750dab TC |
1248 | extensions, as it ensures that you get an error on misspelled function |
1249 | names even if the test suite doesn't call them. | |
02c7413a | 1250 | |
5d170f3a | 1251 | =item PERL_ENCODING |
d74e8afc | 1252 | X<PERL_ENCODING> |
5d170f3a | 1253 | |
f4750dab | 1254 | If using the C<use encoding> pragma without an explicit encoding name, the |
5d170f3a JH |
1255 | PERL_ENCODING environment variable is consulted for an encoding name. |
1256 | ||
504f80c1 | 1257 | =item PERL_HASH_SEED |
d74e8afc | 1258 | X<PERL_HASH_SEED> |
504f80c1 | 1259 | |
6a5b4183 YO |
1260 | (Since Perl 5.8.1, new semantics in Perl 5.18.0) Used to override |
1261 | the randomization of Perl's internal hash function. The value is expressed | |
1262 | in hexadecimal, and may include a leading 0x. Truncated patterns | |
1263 | are treated as though they are suffixed with sufficient 0's as required. | |
8d4a1e6c | 1264 | |
6a5b4183 YO |
1265 | If the option is provided, and C<PERL_PERTURB_KEYS> is NOT set, then |
1266 | a value of '0' implies C<PERL_PERTURB_KEYS=0> and any other value | |
1267 | implies C<PERL_PERTURB_KEYS=2>. | |
504f80c1 | 1268 | |
f4750dab | 1269 | B<PLEASE NOTE: The hash seed is sensitive information>. Hashes are |
26a2d347 | 1270 | randomized to protect against local and remote attacks against Perl |
f4750dab | 1271 | code. By manually setting a seed, this protection may be partially or |
26a2d347 JH |
1272 | completely lost. |
1273 | ||
6a5b4183 | 1274 | See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_PERTURB_KEYS> |
26a2d347 | 1275 | L</PERL_HASH_SEED_DEBUG> for more information. |
504f80c1 | 1276 | |
6a5b4183 YO |
1277 | =item PERL_PERTURB_KEYS |
1278 | X<PERL_PERTURB_KEYS> | |
1279 | ||
1280 | (Since Perl 5.18.0) Set to C<"0"> or C<"NO"> then traversing keys | |
e6b54db6 | 1281 | will be repeatable from run to run for the same PERL_HASH_SEED. |
6a5b4183 YO |
1282 | Insertion into a hash will not change the order, except to provide |
1283 | for more space in the hash. When combined with setting PERL_HASH_SEED | |
1284 | this mode is as close to pre 5.18 behavior as you can get. | |
1285 | ||
1286 | When set to C<"1"> or C<"RANDOM"> then traversing keys will be randomized. | |
1287 | Every time a hash is inserted into the key order will change in a random | |
e6b54db6 | 1288 | fashion. The order may not be repeatable in a following program run |
6a5b4183 YO |
1289 | even if the PERL_HASH_SEED has been specified. This is the default |
1290 | mode for perl. | |
1291 | ||
1292 | When set to C<"2"> or C<"DETERMINISTIC"> then inserting keys into a hash | |
e6b54db6 | 1293 | will cause the key order to change, but in a way that is repeatable |
6a5b4183 YO |
1294 | from program run to program run. |
1295 | ||
1296 | B<NOTE:> Use of this option is considered insecure, and is intended only | |
1297 | for debugging non-deterministic behavior in Perl's hash function. Do | |
1298 | not use it in production. | |
1299 | ||
1300 | See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_HASH_SEED> | |
1301 | and L</PERL_HASH_SEED_DEBUG> for more information. You can get and set the | |
1302 | key traversal mask for a specific hash by using the C<hash_traversal_mask()> | |
1303 | function from L<Hash::Util>. | |
1304 | ||
2191697e | 1305 | =item PERL_HASH_SEED_DEBUG |
d74e8afc | 1306 | X<PERL_HASH_SEED_DEBUG> |
2191697e | 1307 | |
6a5b4183 YO |
1308 | (Since Perl 5.8.1.) Set to C<"1"> to display (to STDERR) information |
1309 | about the hash function, seed, and what type of key traversal | |
1310 | randomization is in effect at the beginning of execution. This, combined | |
1311 | with L</PERL_HASH_SEED> and L</PERL_PERTURB_KEYS> is intended to aid in | |
1312 | debugging nondeterministic behaviour caused by hash randomization. | |
1313 | ||
1314 | B<Note> that any information about the hash function, especially the hash | |
1315 | seed is B<sensitive information>: by knowing it, one can craft a denial-of-service | |
1316 | attack against Perl code, even remotely; see L<perlsec/"Algorithmic Complexity Attacks"> | |
1317 | for more information. B<Do not disclose the hash seed> to people who | |
1318 | don't need to know it. See also C<hash_seed()> and | |
1319 | C<key_traversal_mask()> in L<Hash::Util>. | |
1320 | ||
1321 | An example output might be: | |
26a2d347 | 1322 | |
6a5b4183 | 1323 | HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM) |
2191697e | 1324 | |
9aa9f499 JC |
1325 | =item PERL_MEM_LOG |
1326 | X<PERL_MEM_LOG> | |
1327 | ||
f4750dab | 1328 | If your Perl was configured with B<-Accflags=-DPERL_MEM_LOG>, setting |
7916a455 | 1329 | the environment variable C<PERL_MEM_LOG> enables logging debug |
f4750dab TC |
1330 | messages. The value has the form C<< <I<number>>[m][s][t] >>, where |
1331 | C<I<number>> is the file descriptor number you want to write to (2 is | |
7916a455 JC |
1332 | default), and the combination of letters specifies that you want |
1333 | information about (m)emory and/or (s)v, optionally with | |
f4750dab TC |
1334 | (t)imestamps. For example, C<PERL_MEM_LOG=1mst> logs all |
1335 | information to stdout. You can write to other opened file descriptors | |
1336 | in a variety of ways: | |
9aa9f499 | 1337 | |
f4750dab | 1338 | $ 3>foo3 PERL_MEM_LOG=3m perl ... |
9aa9f499 | 1339 | |
3d0ae7ba | 1340 | =item PERL_ROOT (specific to the VMS port) |
d74e8afc | 1341 | X<PERL_ROOT> |
3d0ae7ba | 1342 | |
f4750dab | 1343 | A translation-concealed rooted logical name that contains Perl and the |
3d0ae7ba | 1344 | logical device for the @INC path on VMS only. Other logical names that |
f4750dab TC |
1345 | affect Perl on VMS include PERLSHR, PERL_ENV_TABLES, and |
1346 | SYS$TIMEZONE_DIFFERENTIAL, but are optional and discussed further in | |
3d0ae7ba GS |
1347 | L<perlvms> and in F<README.vms> in the Perl source distribution. |
1348 | ||
4ffa73a3 | 1349 | =item PERL_SIGNALS |
d74e8afc | 1350 | X<PERL_SIGNALS> |
4ffa73a3 | 1351 | |
f4750dab TC |
1352 | Available in Perls 5.8.1 and later. If set to C<"unsafe">, the pre-Perl-5.8.0 |
1353 | signal behaviour (which is immediate but unsafe) is restored. If set | |
1354 | to C<safe>, then safe (but deferred) signals are used. See | |
1355 | L<perlipc/"Deferred Signals (Safe Signals)">. | |
4ffa73a3 | 1356 | |
a05d7ebb | 1357 | =item PERL_UNICODE |
d74e8afc | 1358 | X<PERL_UNICODE> |
acae81db | 1359 | |
bf61ac64 | 1360 | Equivalent to the B<-C> command-line switch. Note that this is not |
ac036724 | 1361 | a boolean variable. Setting this to C<"1"> is not the right way to |
5b4f334e | 1362 | "enable Unicode" (whatever that would mean). You can use C<"0"> to |
e654d908 | 1363 | "disable Unicode", though (or alternatively unset PERL_UNICODE in |
f4750dab | 1364 | your shell before starting Perl). See the description of the B<-C> |
e654d908 | 1365 | switch for more information. |
acae81db | 1366 | |
3d0ae7ba | 1367 | =item SYS$LOGIN (specific to the VMS port) |
d74e8afc | 1368 | X<SYS$LOGIN> |
3d0ae7ba GS |
1369 | |
1370 | Used if chdir has no argument and HOME and LOGDIR are not set. | |
1371 | ||
a0d0e21e | 1372 | =back |
1e422769 | 1373 | |
1374 | Perl also has environment variables that control how Perl handles data | |
f4750dab TC |
1375 | specific to particular natural languages; see L<perllocale>. |
1376 | ||
1377 | Perl and its various modules and components, including its test frameworks, | |
1378 | may sometimes make use of certain other environment variables. Some of | |
1379 | these are specific to a particular platform. Please consult the | |
1380 | appropriate module documentation and any documentation for your platform | |
1381 | (like L<perlsolaris>, L<perllinux>, L<perlmacosx>, L<perlwin32>, etc) for | |
1382 | variables peculiar to those specific situations. | |
1383 | ||
1384 | Perl makes all environment variables available to the program being | |
1385 | executed, and passes these along to any child processes it starts. | |
1386 | However, programs running setuid would do well to execute the following | |
1387 | lines before doing anything else, just to keep people honest: | |
1388 | ||
1389 | $ENV{PATH} = "/bin:/usr/bin"; # or whatever you need | |
1390 | $ENV{SHELL} = "/bin/sh" if exists $ENV{SHELL}; | |
c90c0ff4 | 1391 | delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; |