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1 | =head1 NAME |
2 | |
3 | perlrun - how to execute the Perl interpreter |
4 | |
5 | =head1 SYNOPSIS |
6 | |
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7 | B<perl> S<[ B<-sTtuUWX> ]> |
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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>] ]> |
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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> ]...> |
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17 | S<[ B<-A [I<assertions>] >]> |
18 | S<[ B<-C [I<number/list>] >]> |
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19 | |
20 | =head1 DESCRIPTION |
21 | |
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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 |
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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. |
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38 | (Note that systems supporting the #! notation invoke interpreters this |
39 | way. See L<Location of Perl>.) |
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40 | |
41 | =item 3. |
42 | |
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43 | Passed in implicitly via standard input. This works only if there are |
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44 | no filename arguments--to pass arguments to a STDIN-read program you |
45 | must explicitly specify a "-" for the program name. |
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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 |
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52 | "perl", and starts there instead. This is useful for running a program |
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53 | embedded in a larger message. (In this case you would indicate the end |
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54 | of the program using the C<__END__> token.) |
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55 | |
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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 |
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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 |
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71 | could also cause odd results. |
72 | |
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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"; }>. |
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77 | |
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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 |
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83 | eval 'exec perl -wS $0 ${1+"$@"}' |
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84 | if $running_under_some_shell; |
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85 | |
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86 | to let Perl see the B<-p> switch. |
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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. |
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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 |
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100 | can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then |
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101 | dispatch the program to the correct interpreter for them. |
102 | |
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103 | After locating your program, Perl compiles the entire program to an |
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104 | internal form. If there are any compilation errors, execution of the |
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105 | program is not attempted. (This is unlike the typical shell script, |
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106 | which might run part-way through before finding a syntax error.) |
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107 | |
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108 | If the program is syntactically correct, it is executed. If the program |
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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 | |
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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 | |
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124 | as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's |
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125 | `extproc' handling). |
126 | |
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127 | =item MS-DOS |
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128 | |
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129 | Create a batch file to run your program, and codify it in |
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130 | C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source |
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131 | distribution for more information). |
132 | |
133 | =item Win95/NT |
134 | |
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135 | The Win95/NT installation, when using the ActiveState installer for Perl, |
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136 | will modify the Registry to associate the F<.pl> extension with the perl |
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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. |
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141 | |
142 | =item Macintosh |
143 | |
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144 | A Macintosh perl program will have the appropriate Creator and |
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145 | Type, so that double-clicking them will invoke the perl application. |
146 | |
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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 = $status = undef; |
153 | |
19799a22 |
154 | at the top of your program, where B<-mysw> are any command line switches you |
155 | want to pass to Perl. You can now invoke the program directly, by saying |
156 | C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly |
157 | via F<DCL$PATH> by just using the name of the program). |
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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 | |
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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 |
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168 | one-liners (see B<-e> below). |
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169 | |
170 | On some systems, you may have to change single-quotes to double ones, |
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171 | which you must I<not> do on Unix or Plan 9 systems. You might also |
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172 | have to change a single % to a %%. |
173 | |
174 | For example: |
175 | |
176 | # Unix |
177 | perl -e 'print "Hello world\n"' |
178 | |
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179 | # MS-DOS, etc. |
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180 | perl -e "print \"Hello world\n\"" |
181 | |
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182 | # Macintosh |
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183 | print "Hello world\n" |
184 | (then Run "Myscript" or Shift-Command-R) |
185 | |
186 | # VMS |
187 | perl -e "print ""Hello world\n""" |
188 | |
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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: |
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192 | |
193 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
194 | |
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195 | B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in |
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196 | when nobody was looking, but just try to find documentation for its |
197 | quoting rules. |
198 | |
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199 | Under the Macintosh, it depends which environment you are using. The MacPerl |
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200 | shell, or MPW, is much like Unix shells in its support for several |
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201 | quoting variants, except that it makes free use of the Macintosh's non-ASCII |
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202 | characters as control characters. |
203 | |
204 | There is no general solution to all of this. It's just a mess. |
205 | |
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206 | =head2 Location of Perl |
207 | |
208 | It may seem obvious to say, but Perl is useful only when users can |
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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. |
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219 | |
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220 | #!/usr/local/bin/perl5.00554 |
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221 | |
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222 | or if you just want to be running at least version, place a statement |
223 | like this at the top of your program: |
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224 | |
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225 | use 5.005_54; |
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226 | |
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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 |
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233 | |
234 | Switches include: |
235 | |
236 | =over 5 |
237 | |
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238 | =item B<-0>[I<octal/hexadecimal>] |
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239 | |
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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: |
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245 | |
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246 | find . -name '*.orig' -print0 | perl -n0e unlink |
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247 | |
248 | The special value 00 will cause Perl to slurp files in paragraph mode. |
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249 | The value 0777 will cause Perl to slurp files whole because there is no |
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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.) |
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256 | |
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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 | |
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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 | |
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280 | =item B<-C [I<number/list>]> |
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281 | |
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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 |
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285 | of option letters. The letters, their numeric values, and effects |
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286 | are as follows; listing the letters is equal to summing the numbers. |
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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 |
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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 |
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294 | D 24 i + o |
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295 | A 32 the @ARGV elements are expected to be strings encoded in UTF-8 |
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296 | L 64 normally the "IOEioA" are unconditional, |
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297 | the L makes them conditional on the locale environment |
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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 |
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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. |
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305 | |
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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 | |
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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 |
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 |
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317 | variables indicate a UTF-8 locale. This behaviour follows the |
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318 | I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0. |
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319 | |
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320 | You can use C<-C0> (or C<"0"> for $ENV{PERL_UNICODE}) to explicitly |
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321 | disable all the above Unicode features. |
fde18df1 |
322 | |
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323 | The read-only magic variable C<${^UNICODE}> reflects the numeric value |
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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 |
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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 |
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".) |
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333 | |
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334 | =item B<-c> |
335 | |
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336 | causes Perl to check the syntax of the program and then exit without |
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337 | executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and |
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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. |
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341 | |
342 | =item B<-d> |
343 | |
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344 | runs the program under the Perl debugger. See L<perldebug>. |
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345 | |
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346 | =item B<-d:>I<foo[=bar,baz]> |
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347 | |
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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 |
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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>. |
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355 | |
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356 | =item B<-D>I<letters> |
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357 | |
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358 | =item B<-D>I<number> |
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359 | |
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360 | sets debugging flags. To watch how it executes your program, use |
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361 | B<-Dtls>. (This works only if debugging is compiled into your |
362 | Perl.) Another nice value is B<-Dx>, which lists your compiled |
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363 | syntax tree. And B<-Dr> displays compiled regular expressions; |
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364 | the format of the output is explained in L<perldebguts>. |
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365 | |
366 | As an alternative, specify a number instead of list of letters (e.g., |
367 | B<-D14> is equivalent to B<-Dtls>): |
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368 | |
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369 | 1 p Tokenizing and parsing |
370 | 2 s Stack snapshots |
d6721266 |
371 | with v, displays all stacks |
db2ba183 |
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 |
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376 | 64 P Print profiling info, preprocessor command for -P, source file input state |
db2ba183 |
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 |
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382 | 4096 (Obsolete, previously used for LEAKTEST) |
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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 |
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388 | 262144 R Include reference counts of dumped variables (eg when using -Ds) |
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389 | 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB |
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390 | 1048576 v Verbose: use in conjunction with other flags |
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391 | 2097152 C Copy On Write |
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392 | |
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393 | All these flags require B<-DDEBUGGING> when you compile the Perl |
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394 | executable (but see L<Devel::Peek>, L<re> which may change this). |
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395 | See the F<INSTALL> file in the Perl source distribution |
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396 | for how to do this. This flag is automatically set if you include B<-g> |
8c52afec |
397 | option when C<Configure> asks you about optimizer/debugger flags. |
398 | |
19799a22 |
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 |
403 | # If you have "env" utility |
404 | env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program |
405 | |
19799a22 |
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 |
414 | =item B<-e> I<commandline> |
415 | |
19799a22 |
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 |
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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 |
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 | |
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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 |
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 |
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 |
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 |
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 |
476 | s/foo/bar/; |
477 | |
478 | which is equivalent to |
479 | |
480 | #!/usr/bin/perl |
19799a22 |
481 | $extension = '.orig'; |
482 | LINE: while (<>) { |
a0d0e21e |
483 | if ($ARGV ne $oldargv) { |
66606d78 |
484 | if ($extension !~ /\*/) { |
485 | $backup = $ARGV . $extension; |
486 | } |
487 | else { |
488 | ($backup = $extension) =~ s/\*/$ARGV/g; |
489 | } |
490 | rename($ARGV, $backup); |
a0d0e21e |
491 | open(ARGVOUT, ">$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 |
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 |
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 |
524 | |
525 | You cannot use B<-i> to create directories or to strip extensions from |
526 | files. |
a0d0e21e |
527 | |
19799a22 |
528 | Perl does not expand C<~> in filenames, which is good, since some |
529 | folks use it for their backup files: |
a0d0e21e |
530 | |
19799a22 |
531 | $ perl -pi~ -e 's/foo/bar/' file1 file2 file3... |
532 | |
533 | Finally, the B<-i> switch does not impede execution when no |
a2008d6d |
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 |
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 |
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 |
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 |
573 | B<-m>I<module> executes C<use> I<module> C<();> before executing your |
574 | program. |
3c81428c |
575 | |
19799a22 |
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 |
581 | then the 'use' is replaced with 'no'. |
582 | |
54310121 |
583 | A little builtin syntactic sugar means you can also say |
19799a22 |
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 |
590 | =item B<-n> |
591 | |
19799a22 |
592 | causes Perl to assume the following loop around your program, which |
a0d0e21e |
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 |
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 |
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 |
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 |
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 |
616 | |
617 | =item B<-p> |
618 | |
19799a22 |
619 | causes Perl to assume the following loop around your program, which |
a0d0e21e |
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 |
628 | } |
629 | |
08e9d68e |
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 |
633 | treated as fatal. To suppress printing use the B<-n> switch. A B<-p> |
634 | overrides a B<-n> switch. |
a0d0e21e |
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 |
638 | |
639 | =item B<-P> |
640 | |
079a94c4 |
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 |
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 |
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 |
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 |
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 |
704 | =item B<-s> |
705 | |
19799a22 |
706 | enables rudimentary switch parsing for switches on the command |
707 | line after the program name but before any filename arguments (or before |
3bbcc830 |
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 |
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 |
713 | |
714 | #!/usr/bin/perl -s |
3c0facb2 |
715 | if ($xyz) { print "$xyz\n" } |
a0d0e21e |
716 | |
3bbcc830 |
717 | Do note that B<--help> creates the variable ${-help}, which is not compliant |
718 | with C<strict refs>. |
719 | |
a0d0e21e |
720 | =item B<-S> |
721 | |
722 | makes Perl use the PATH environment variable to search for the |
19799a22 |
723 | program (unless the name of the program contains directory separators). |
724 | |
2a92aaa0 |
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 |
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 |
735 | |
736 | #!/usr/bin/perl |
a3cb178b |
737 | eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}' |
a0d0e21e |
738 | if $running_under_some_shell; |
739 | |
19799a22 |
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 |
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 $running_under_some_shell |
19799a22 |
747 | is never true. If the program will be interpreted by csh, you will need |
a3cb178b |
748 | to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand |
749 | embedded spaces (and such) in the argument list. To start up sh rather |
a0d0e21e |
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 |
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 |
769 | =item B<-t> |
770 | |
771 | Like B<-T>, but taint checks will issue warnings rather than fatal |
317ea90d |
772 | errors. These warnings can be controlled normally with C<no warnings |
773 | qw(taint)>. |
1dbad523 |
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 |
780 | =item B<-T> |
781 | |
a3cb178b |
782 | forces "taint" checks to be turned on so you can test them. Ordinarily |
19799a22 |
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 |
791 | |
792 | =item B<-u> |
793 | |
19799a22 |
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 |
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 |
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 |
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 |
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 |
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<$^W> variable. You |
19799a22 |
847 | can disable or promote into fatal errors specific warnings using |
848 | C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>. |
849 | See also L<perldiag> and L<perltrap>. A new, fine-grained warning |
850 | facility is also available if you want to manipulate entire classes |
9f1b1f2d |
851 | of warnings; see L<warnings> or L<perllexwarn>. |
a0d0e21e |
852 | |
0453d815 |
853 | =item B<-W> |
854 | |
3c0facb2 |
855 | Enables all warnings regardless of C<no warnings> or C<$^W>. |
0453d815 |
856 | See L<perllexwarn>. |
857 | |
858 | =item B<-X> |
859 | |
3c0facb2 |
860 | Disables all warnings regardless of C<use warnings> or C<$^W>. |
0453d815 |
861 | See L<perllexwarn>. |
862 | |
a0d0e21e |
863 | =item B<-x> I<directory> |
864 | |
19799a22 |
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 |
899 | directory. Any architecture-specific directories under the specified |
900 | locations are automatically included if they exist. If PERL5LIB is not |
48b971ca |
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 |
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 |
917 | variable is ignored. If PERL5OPT begins with B<-T>, tainting will be |
918 | enabled, and any subsequent options ignored. |
54310121 |
919 | |
16537909 |
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 |
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 |
930 | An unset or empty PERLIO is equivalent to C<:stdio>. |
931 | |
44a4342c |
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 |
939 | |
940 | =over 8 |
941 | |
942 | =item :bytes |
943 | |
18aba96f |
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 |
947 | |
948 | =item :crlf |
949 | |
8229d19f |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
1027 | |
1028 | =item :utf8 |
1029 | |
18aba96f |
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 |
1037 | |
1038 | =item :win32 |
1039 | |
ab4f7683 |
1040 | On Win32 platforms this I<experimental> layer uses native "handle" IO |
44a4342c |
1041 | rather than unix-like numeric file descriptor layer. Known to be |
1042 | buggy in this release. |
16537909 |
1043 | |
1044 | =back |
1045 | |
44a4342c |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
1125 | =item PERL_HASH_SEED |
1126 | |
183c3da1 |
1127 | (Since Perl 5.8.1.) Used to randomise Perl's internal hash function. |
4546b9e6 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
1167 | affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and |
1168 | SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in |
3d0ae7ba |
1169 | L<perlvms> and in F<README.vms> in the Perl source distribution. |
1170 | |
4ffa73a3 |
1171 | =item PERL_SIGNALS |
1172 | |
1173 | In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0 |
1174 | signals behaviour (immediate but unsafe) is restored. If set to |
ec488bcf |
1175 | C<safe> the safe (or deferred) signals are used. |
1176 | See L<perlipc/"Deferred Signals (Safe signals)">. |
4ffa73a3 |
1177 | |
a05d7ebb |
1178 | =item PERL_UNICODE |
acae81db |
1179 | |
bf61ac64 |
1180 | Equivalent to the B<-C> command-line switch. Note that this is not |
1181 | a boolean variable-- setting this to C<"1"> is not the right way to |
5b4f334e |
1182 | "enable Unicode" (whatever that would mean). You can use C<"0"> to |
e654d908 |
1183 | "disable Unicode", though (or alternatively unset PERL_UNICODE in |
1184 | your shell before starting Perl). See the description of the C<-C> |
1185 | switch for more information. |
acae81db |
1186 | |
3d0ae7ba |
1187 | =item SYS$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 |
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)}; |