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1 | =head1 NAME |
2 | |
3 | perl - Practical Extraction and Report Language |
4 | |
5 | =head1 SYNOPSIS |
6 | |
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7 | B<perl> S<[ B<-sTuU> ]> |
8 | S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]> |
9 | S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]> |
10 | S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]> |
11 | S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]> |
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 | |
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18 | For ease of access, the Perl manual has been split up into a number |
19 | of sections: |
20 | |
21 | perl Perl overview (this section) |
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22 | perlnews Perl news about changes from previous version |
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23 | |
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24 | perldata Perl data structures |
25 | perlsyn Perl syntax |
26 | perlop Perl operators and precedence |
27 | perlre Perl regular expressions |
28 | perlrun Perl execution and options |
29 | perlfunc Perl builtin functions |
30 | perlvar Perl predefined variables |
31 | perlsub Perl subroutines |
32 | perlmod Perl modules |
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33 | perlform Perl formats |
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34 | perllocale Perl locale support |
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35 | |
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36 | perlref Perl references |
37 | perldsc Perl data structures intro |
38 | perllol Perl data structures: lists of lists |
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39 | perltoot Perl OO tutorial |
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40 | perlobj Perl objects |
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41 | perltie Perl objects hidden behind simple variables |
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42 | perlbot Perl OO tricks and examples |
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43 | perlipc Perl interprocess communication |
44 | |
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45 | perldebug Perl debugging |
46 | perldiag Perl diagnostic messages |
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47 | perlsec Perl security |
48 | perltrap Perl traps for the unwary |
49 | perlstyle Perl style guide |
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50 | |
51 | perlpod Perl plain old documentation |
52 | perlbook Perl book information |
53 | |
54 | perlembed Perl how to embed perl in your C or C++ app |
55 | perlapio Perl internal IO abstraction interface |
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56 | perlxs Perl XS application programming interface |
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57 | perlxstut Perl XS tutorial |
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58 | perlguts Perl internal functions for those doing extensions |
59 | perlcall Perl calling conventions from C |
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60 | |
61 | (If you're intending to read these straight through for the first time, |
62 | the suggested order will tend to reduce the number of forward references.) |
63 | |
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64 | Additional documentation for Perl modules is available in the |
65 | F</usr/local/man/> directory. Some of this is distributed standard with |
66 | Perl, but you'll also find third-party modules there. You should be able |
67 | to view this with your man(1) program by including the proper directories |
68 | in the appropriate start-up files. To find out where these are, type: |
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69 | |
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70 | perl -V:man.dir |
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71 | |
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72 | If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>, |
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73 | you would need to add only F</usr/local/man> to your MANPATH. If |
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74 | they are different, you'll have to add both stems. |
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75 | |
76 | If that doesn't work for some reason, you can still use the |
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77 | supplied F<perldoc> script to view module information. You might |
78 | also look into getting a replacement man program. |
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79 | |
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80 | If something strange has gone wrong with your program and you're not |
81 | sure where you should look for help, try the B<-w> switch first. It |
82 | will often point out exactly where the trouble is. |
83 | |
84 | =head1 DESCRIPTION |
85 | |
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86 | Perl is a language optimized for scanning arbitrary |
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87 | text files, extracting information from those text files, and printing |
88 | reports based on that information. It's also a good language for many |
89 | system management tasks. The language is intended to be practical |
90 | (easy to use, efficient, complete) rather than beautiful (tiny, |
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91 | elegant, minimal). |
92 | |
93 | Perl combines (in the author's opinion, anyway) some |
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94 | of the best features of C, B<sed>, B<awk>, and B<sh>, so people |
95 | familiar with those languages should have little difficulty with it. |
96 | (Language historians will also note some vestiges of B<csh>, Pascal, |
97 | and even BASIC-PLUS.) Expression syntax corresponds quite closely to C |
98 | expression syntax. Unlike most Unix utilities, Perl does not |
99 | arbitrarily limit the size of your data--if you've got the memory, |
100 | Perl can slurp in your whole file as a single string. Recursion is |
101 | of unlimited depth. And the hash tables used by associative arrays |
102 | grow as necessary to prevent degraded performance. Perl uses |
103 | sophisticated pattern matching techniques to scan large amounts of data |
104 | very quickly. Although optimized for scanning text, Perl can also |
105 | deal with binary data, and can make dbm files look like associative |
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106 | arrays. Setuid Perl scripts are safer than |
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107 | C programs through a dataflow tracing mechanism which prevents many |
108 | stupid security holes. If you have a problem that would ordinarily use |
109 | B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must |
110 | run a little faster, and you don't want to write the silly thing in C, |
111 | then Perl may be for you. There are also translators to turn your |
112 | B<sed> and B<awk> scripts into Perl scripts. |
113 | |
114 | But wait, there's more... |
115 | |
116 | Perl version 5 is nearly a complete rewrite, and provides |
117 | the following additional benefits: |
118 | |
119 | =over 5 |
120 | |
121 | =item * Many usability enhancements |
122 | |
123 | It is now possible to write much more readable Perl code (even within |
124 | regular expressions). Formerly cryptic variable names can be replaced |
125 | by mnemonic identifiers. Error messages are more informative, and the |
126 | optional warnings will catch many of the mistakes a novice might make. |
127 | This cannot be stressed enough. Whenever you get mysterious behavior, |
128 | try the B<-w> switch!!! Whenever you don't get mysterious behavior, |
129 | try using B<-w> anyway. |
130 | |
131 | =item * Simplified grammar |
132 | |
133 | The new yacc grammar is one half the size of the old one. Many of the |
134 | arbitrary grammar rules have been regularized. The number of reserved |
135 | words has been cut by 2/3. Despite this, nearly all old Perl scripts |
136 | will continue to work unchanged. |
137 | |
138 | =item * Lexical scoping |
139 | |
140 | Perl variables may now be declared within a lexical scope, like "auto" |
141 | variables in C. Not only is this more efficient, but it contributes |
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142 | to better privacy for "programming in the large". Anonymous |
143 | subroutines exhibit deep binding of lexical variables (closures). |
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144 | |
145 | =item * Arbitrarily nested data structures |
146 | |
147 | Any scalar value, including any array element, may now contain a |
148 | reference to any other variable or subroutine. You can easily create |
149 | anonymous variables and subroutines. Perl manages your reference |
150 | counts for you. |
151 | |
152 | =item * Modularity and reusability |
153 | |
154 | The Perl library is now defined in terms of modules which can be easily |
155 | shared among various packages. A package may choose to import all or a |
156 | portion of a module's published interface. Pragmas (that is, compiler |
157 | directives) are defined and used by the same mechanism. |
158 | |
159 | =item * Object-oriented programming |
160 | |
161 | A package can function as a class. Dynamic multiple inheritance and |
162 | virtual methods are supported in a straightforward manner and with very |
163 | little new syntax. Filehandles may now be treated as objects. |
164 | |
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165 | =item * Embeddable and Extensible |
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166 | |
167 | Perl may now be embedded easily in your C or C++ application, and can |
168 | either call or be called by your routines through a documented |
169 | interface. The XS preprocessor is provided to make it easy to glue |
170 | your C or C++ routines into Perl. Dynamic loading of modules is |
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171 | supported, and Perl itself can be made into a dynamic library. |
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172 | |
173 | =item * POSIX compliant |
174 | |
175 | A major new module is the POSIX module, which provides access to all |
176 | available POSIX routines and definitions, via object classes where |
177 | appropriate. |
178 | |
179 | =item * Package constructors and destructors |
180 | |
181 | The new BEGIN and END blocks provide means to capture control as |
182 | a package is being compiled, and after the program exits. As a |
183 | degenerate case they work just like awk's BEGIN and END when you |
184 | use the B<-p> or B<-n> switches. |
185 | |
186 | =item * Multiple simultaneous DBM implementations |
187 | |
188 | A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB |
189 | files from the same script simultaneously. In fact, the old dbmopen |
190 | interface has been generalized to allow any variable to be tied |
191 | to an object class which defines its access methods. |
192 | |
193 | =item * Subroutine definitions may now be autoloaded |
194 | |
195 | In fact, the AUTOLOAD mechanism also allows you to define any arbitrary |
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196 | semantics for undefined subroutine calls. It's not for just autoloading. |
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197 | |
198 | =item * Regular expression enhancements |
199 | |
200 | You can now specify non-greedy quantifiers. You can now do grouping |
201 | without creating a backreference. You can now write regular expressions |
202 | with embedded whitespace and comments for readability. A consistent |
203 | extensibility mechanism has been added that is upwardly compatible with |
204 | all old regular expressions. |
205 | |
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206 | =item * Innumerable Unbundled Modules |
207 | |
208 | The Comprehensive Perl Archive Network described in L<perlmod> |
209 | contains hundreds of plug-and-play modules full of reusable |
210 | code. See F<http://www.perl.com/CPAN> for a site near you. |
211 | |
212 | =item * Compilability |
213 | |
214 | While not yet in full production mode, a working perl-to-C compiler |
215 | does exist. It can generate portable bytecode, simple C, or |
216 | optimized C code. |
217 | |
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218 | =back |
219 | |
220 | Ok, that's I<definitely> enough hype. |
221 | |
222 | =head1 ENVIRONMENT |
223 | |
224 | =over 12 |
225 | |
226 | =item HOME |
227 | |
228 | Used if chdir has no argument. |
229 | |
230 | =item LOGDIR |
231 | |
232 | Used if chdir has no argument and HOME is not set. |
233 | |
234 | =item PATH |
235 | |
236 | Used in executing subprocesses, and in finding the script if B<-S> is |
237 | used. |
238 | |
239 | =item PERL5LIB |
240 | |
241 | A colon-separated list of directories in which to look for Perl library |
242 | files before looking in the standard library and the current |
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243 | directory. If PERL5LIB is not defined, PERLLIB is used. When running |
244 | taint checks (because the script was running setuid or setgid, or the |
245 | B<-T> switch was used), neither variable is used. The script should |
246 | instead say |
247 | |
248 | use lib "/my/directory"; |
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249 | |
250 | =item PERL5DB |
251 | |
252 | The command used to get the debugger code. If unset, uses |
253 | |
254 | BEGIN { require 'perl5db.pl' } |
255 | |
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256 | =item PERL_DESTRUCT_LEVEL |
257 | |
258 | Relevant only if your perl executable was built with B<-DDEBUGGING>, |
259 | this controls the behavior of global destruction of objects and other |
260 | references. |
261 | |
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262 | =item PERLLIB |
263 | |
264 | A colon-separated list of directories in which to look for Perl library |
265 | files before looking in the standard library and the current |
266 | directory. If PERL5LIB is defined, PERLLIB is not used. |
267 | |
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268 | =back |
269 | |
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270 | Perl also has environment variables that control how Perl handles |
271 | language-specific data. Please consult the L<perli18n> section. |
272 | |
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273 | Apart from these, Perl uses no other environment variables, except |
274 | to make them available to the script being executed, and to child |
275 | processes. However, scripts running setuid would do well to execute |
276 | the following lines before doing anything else, just to keep people |
277 | honest: |
278 | |
279 | $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need |
280 | $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'}; |
281 | $ENV{'IFS'} = '' if defined $ENV{'IFS'}; |
282 | |
283 | =head1 AUTHOR |
284 | |
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285 | Larry Wall E<lt>F<larry@wall.org>E<gt>, with the help of oodles of other folks. |
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286 | |
287 | =head1 FILES |
288 | |
289 | "/tmp/perl-e$$" temporary file for -e commands |
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290 | "@INC" locations of perl libraries |
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291 | |
292 | =head1 SEE ALSO |
293 | |
294 | a2p awk to perl translator |
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295 | |
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296 | s2p sed to perl translator |
297 | |
298 | =head1 DIAGNOSTICS |
299 | |
300 | The B<-w> switch produces some lovely diagnostics. |
301 | |
302 | See L<perldiag> for explanations of all Perl's diagnostics. |
303 | |
304 | Compilation errors will tell you the line number of the error, with an |
305 | indication of the next token or token type that was to be examined. |
306 | (In the case of a script passed to Perl via B<-e> switches, each |
307 | B<-e> is counted as one line.) |
308 | |
309 | Setuid scripts have additional constraints that can produce error |
310 | messages such as "Insecure dependency". See L<perlsec>. |
311 | |
312 | Did we mention that you should definitely consider using the B<-w> |
313 | switch? |
314 | |
315 | =head1 BUGS |
316 | |
317 | The B<-w> switch is not mandatory. |
318 | |
319 | Perl is at the mercy of your machine's definitions of various |
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320 | operations such as type casting, atof(), and sprintf(). The latter |
321 | can even trigger a core dump when passed ludicrous input values. |
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322 | |
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323 | If your stdio requires a seek or eof between reads and writes on a |
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324 | particular stream, so does Perl. (This doesn't apply to sysread() |
325 | and syswrite().) |
326 | |
327 | While none of the built-in data types have any arbitrary size limits |
328 | (apart from memory size), there are still a few arbitrary limits: a |
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329 | given variable name may not be longer than 255 characters, and no |
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330 | component of your PATH may be longer than 255 if you use B<-S>. A regular |
331 | expression may not compile to more than 32767 bytes internally. |
332 | |
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333 | See the perl bugs database at F<http://www.perl.com/perl/bugs/>. You may |
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334 | mail your bug reports (be sure to include full configuration information |
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335 | as output by the myconfig program in the perl source tree, or by C<perl -V>) to |
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336 | F<perlbug@perl.com>. |
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337 | If you've succeeded in compiling perl, the perlbug script in the utils/ |
338 | subdirectory can be used to help mail in a bug report. |
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339 | |
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340 | Perl actually stands for Pathologically Eclectic Rubbish Lister, but |
341 | don't tell anyone I said that. |
342 | |
343 | =head1 NOTES |
344 | |
345 | The Perl motto is "There's more than one way to do it." Divining |
346 | how many more is left as an exercise to the reader. |
347 | |
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348 | The three principal virtues of a programmer are Laziness, |
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349 | Impatience, and Hubris. See the Camel Book for why. |
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350 | |