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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 | perldelta Perl changes since previous version |
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23 | perlfaq Perl frequently asked questions |
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24 | |
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25 | perldata Perl data structures |
26 | perlsyn Perl syntax |
27 | perlop Perl operators and precedence |
28 | perlre Perl regular expressions |
29 | perlrun Perl execution and options |
30 | perlfunc Perl builtin functions |
31 | perlvar Perl predefined variables |
32 | perlsub Perl subroutines |
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33 | perlmod Perl modules: how they work |
34 | perlmodlib Perl modules: how to write and use |
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35 | perlform Perl formats |
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36 | perllocale Perl locale support |
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37 | |
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38 | perlref Perl references |
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39 | perldsc Perl data structures intro |
40 | perllol Perl data structures: lists of lists |
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41 | perltoot Perl OO tutorial |
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42 | perlobj Perl objects |
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43 | perltie Perl objects hidden behind simple variables |
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44 | perlbot Perl OO tricks and examples |
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45 | perlipc Perl interprocess communication |
46 | |
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47 | perldebug Perl debugging |
48 | perldiag Perl diagnostic messages |
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49 | perlsec Perl security |
50 | perltrap Perl traps for the unwary |
51 | perlstyle Perl style guide |
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52 | |
53 | perlpod Perl plain old documentation |
54 | perlbook Perl book information |
55 | |
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56 | perlembed Perl ways to embed perl in your C or C++ application |
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57 | perlapio Perl internal IO abstraction interface |
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58 | perlxs Perl XS application programming interface |
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59 | perlxstut Perl XS tutorial |
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60 | perlguts Perl internal functions for those doing extensions |
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61 | perlcall Perl calling conventions from C |
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62 | |
63 | (If you're intending to read these straight through for the first time, |
64 | the suggested order will tend to reduce the number of forward references.) |
65 | |
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66 | By default, all of the above manpages are installed in the |
67 | F</usr/local/man/> directory. |
68 | |
69 | Extensive additional documentation for Perl modules is available. The |
70 | default configuration for perl will place this additional documentation |
71 | in the F</usr/local/lib/perl5/man> directory (or else in the F<man> |
72 | subdirectory of the Perl library directory). Some of this additional |
73 | documentation is distributed standard with Perl, but you'll also find |
74 | documentation for third-party modules there. |
75 | |
76 | You should be able to view Perl's documentation with your man(1) |
77 | program by including the proper directories in the appropriate start-up |
78 | files, or in the MANPATH environment variable. To find out where the |
79 | configuration has installed the manpages, type: |
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80 | |
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81 | perl -V:man.dir |
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82 | |
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83 | If the directories have a common stem, such as F</usr/local/man/man1> |
84 | and F</usr/local/man/man3>, you need only to add that stem |
85 | (F</usr/local/man>) to your man(1) configuration files or your MANPATH |
86 | environment variable. If they do not share a stem, you'll have to add |
87 | both stems. |
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88 | |
89 | If that doesn't work for some reason, you can still use the |
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90 | supplied F<perldoc> script to view module information. You might |
91 | also look into getting a replacement man program. |
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92 | |
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93 | If something strange has gone wrong with your program and you're not |
94 | sure where you should look for help, try the B<-w> switch first. It |
95 | will often point out exactly where the trouble is. |
96 | |
97 | =head1 DESCRIPTION |
98 | |
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99 | Perl is a language optimized for scanning arbitrary |
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100 | text files, extracting information from those text files, and printing |
101 | reports based on that information. It's also a good language for many |
102 | system management tasks. The language is intended to be practical |
103 | (easy to use, efficient, complete) rather than beautiful (tiny, |
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104 | elegant, minimal). |
105 | |
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106 | Perl combines (in the author's opinion, anyway) some of the best |
107 | features of C, B<sed>, B<awk>, and B<sh>, so people familiar with |
108 | those languages should have little difficulty with it. (Language |
109 | historians will also note some vestiges of B<csh>, Pascal, and even |
110 | BASIC-PLUS.) Expression syntax corresponds quite closely to C |
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111 | expression syntax. Unlike most Unix utilities, Perl does not |
112 | arbitrarily limit the size of your data--if you've got the memory, |
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113 | Perl can slurp in your whole file as a single string. Recursion is of |
114 | unlimited depth. And the tables used by hashes (previously called |
115 | "associative arrays") grow as necessary to prevent degraded |
116 | performance. Perl uses sophisticated pattern matching techniques to |
117 | scan large amounts of data very quickly. Although optimized for |
118 | scanning text, Perl can also deal with binary data, and can make dbm |
119 | files look like hashes. Setuid Perl scripts are safer than C programs |
120 | through a dataflow tracing mechanism which prevents many stupid |
121 | security holes. |
122 | |
123 | If you have a problem that would ordinarily use B<sed> or B<awk> or |
124 | B<sh>, but it exceeds their capabilities or must run a little faster, |
125 | and you don't want to write the silly thing in C, then Perl may be for |
126 | you. There are also translators to turn your B<sed> and B<awk> |
127 | scripts into Perl scripts. |
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128 | |
129 | But wait, there's more... |
130 | |
131 | Perl version 5 is nearly a complete rewrite, and provides |
132 | the following additional benefits: |
133 | |
134 | =over 5 |
135 | |
136 | =item * Many usability enhancements |
137 | |
138 | It is now possible to write much more readable Perl code (even within |
139 | regular expressions). Formerly cryptic variable names can be replaced |
140 | by mnemonic identifiers. Error messages are more informative, and the |
141 | optional warnings will catch many of the mistakes a novice might make. |
142 | This cannot be stressed enough. Whenever you get mysterious behavior, |
143 | try the B<-w> switch!!! Whenever you don't get mysterious behavior, |
144 | try using B<-w> anyway. |
145 | |
146 | =item * Simplified grammar |
147 | |
148 | The new yacc grammar is one half the size of the old one. Many of the |
149 | arbitrary grammar rules have been regularized. The number of reserved |
150 | words has been cut by 2/3. Despite this, nearly all old Perl scripts |
151 | will continue to work unchanged. |
152 | |
153 | =item * Lexical scoping |
154 | |
155 | Perl variables may now be declared within a lexical scope, like "auto" |
156 | variables in C. Not only is this more efficient, but it contributes |
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157 | to better privacy for "programming in the large". Anonymous |
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158 | subroutines exhibit deep binding of lexical variables (closures). |
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159 | |
160 | =item * Arbitrarily nested data structures |
161 | |
162 | Any scalar value, including any array element, may now contain a |
163 | reference to any other variable or subroutine. You can easily create |
164 | anonymous variables and subroutines. Perl manages your reference |
165 | counts for you. |
166 | |
167 | =item * Modularity and reusability |
168 | |
169 | The Perl library is now defined in terms of modules which can be easily |
170 | shared among various packages. A package may choose to import all or a |
171 | portion of a module's published interface. Pragmas (that is, compiler |
172 | directives) are defined and used by the same mechanism. |
173 | |
174 | =item * Object-oriented programming |
175 | |
176 | A package can function as a class. Dynamic multiple inheritance and |
177 | virtual methods are supported in a straightforward manner and with very |
178 | little new syntax. Filehandles may now be treated as objects. |
179 | |
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180 | =item * Embeddable and Extensible |
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181 | |
182 | Perl may now be embedded easily in your C or C++ application, and can |
183 | either call or be called by your routines through a documented |
184 | interface. The XS preprocessor is provided to make it easy to glue |
185 | your C or C++ routines into Perl. Dynamic loading of modules is |
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186 | supported, and Perl itself can be made into a dynamic library. |
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187 | |
188 | =item * POSIX compliant |
189 | |
190 | A major new module is the POSIX module, which provides access to all |
191 | available POSIX routines and definitions, via object classes where |
192 | appropriate. |
193 | |
194 | =item * Package constructors and destructors |
195 | |
196 | The new BEGIN and END blocks provide means to capture control as |
197 | a package is being compiled, and after the program exits. As a |
198 | degenerate case they work just like awk's BEGIN and END when you |
199 | use the B<-p> or B<-n> switches. |
200 | |
201 | =item * Multiple simultaneous DBM implementations |
202 | |
203 | A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB |
204 | files from the same script simultaneously. In fact, the old dbmopen |
205 | interface has been generalized to allow any variable to be tied |
206 | to an object class which defines its access methods. |
207 | |
208 | =item * Subroutine definitions may now be autoloaded |
209 | |
210 | In fact, the AUTOLOAD mechanism also allows you to define any arbitrary |
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211 | semantics for undefined subroutine calls. It's not for just autoloading. |
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212 | |
213 | =item * Regular expression enhancements |
214 | |
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215 | You can now specify nongreedy quantifiers. You can now do grouping |
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216 | without creating a backreference. You can now write regular expressions |
217 | with embedded whitespace and comments for readability. A consistent |
218 | extensibility mechanism has been added that is upwardly compatible with |
219 | all old regular expressions. |
220 | |
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221 | =item * Innumerable Unbundled Modules |
222 | |
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223 | The Comprehensive Perl Archive Network described in L<perlmodlib> |
224 | contains hundreds of plug-and-play modules full of reusable code. |
225 | See F<http://www.perl.com/CPAN> for a site near you. |
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226 | |
227 | =item * Compilability |
228 | |
229 | While not yet in full production mode, a working perl-to-C compiler |
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230 | does exist. It can generate portable byte code, simple C, or |
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231 | optimized C code. |
232 | |
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233 | =back |
234 | |
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235 | Okay, that's I<definitely> enough hype. |
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236 | |
237 | =head1 ENVIRONMENT |
238 | |
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239 | See L<perlrun>. |
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240 | |
241 | =head1 AUTHOR |
242 | |
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243 | Larry Wall <F<larry@wall.org>>, with the help of oodles of other folks. |
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244 | |
245 | =head1 FILES |
246 | |
247 | "/tmp/perl-e$$" temporary file for -e commands |
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248 | "@INC" locations of perl libraries |
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249 | |
250 | =head1 SEE ALSO |
251 | |
252 | a2p awk to perl translator |
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253 | |
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254 | s2p sed to perl translator |
255 | |
256 | =head1 DIAGNOSTICS |
257 | |
258 | The B<-w> switch produces some lovely diagnostics. |
259 | |
260 | See L<perldiag> for explanations of all Perl's diagnostics. |
261 | |
262 | Compilation errors will tell you the line number of the error, with an |
263 | indication of the next token or token type that was to be examined. |
264 | (In the case of a script passed to Perl via B<-e> switches, each |
265 | B<-e> is counted as one line.) |
266 | |
267 | Setuid scripts have additional constraints that can produce error |
268 | messages such as "Insecure dependency". See L<perlsec>. |
269 | |
270 | Did we mention that you should definitely consider using the B<-w> |
271 | switch? |
272 | |
273 | =head1 BUGS |
274 | |
275 | The B<-w> switch is not mandatory. |
276 | |
277 | Perl is at the mercy of your machine's definitions of various |
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278 | operations such as type casting, atof(), and floating-point |
279 | output with sprintf(). |
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280 | |
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281 | If your stdio requires a seek or eof between reads and writes on a |
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282 | particular stream, so does Perl. (This doesn't apply to sysread() |
283 | and syswrite().) |
284 | |
285 | While none of the built-in data types have any arbitrary size limits |
286 | (apart from memory size), there are still a few arbitrary limits: a |
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287 | given variable name may not be longer than 255 characters, and no |
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288 | component of your PATH may be longer than 255 if you use B<-S>. A regular |
289 | expression may not compile to more than 32767 bytes internally. |
290 | |
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291 | You may mail your bug reports (be sure to include full configuration |
292 | information as output by the myconfig program in the perl source tree, |
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293 | or by C<perl -V>) to <F<perlbug@perl.com>>. |
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294 | If you've succeeded in compiling perl, the perlbug script in the utils/ |
295 | subdirectory can be used to help mail in a bug report. |
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296 | |
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297 | Perl actually stands for Pathologically Eclectic Rubbish Lister, but |
298 | don't tell anyone I said that. |
299 | |
300 | =head1 NOTES |
301 | |
302 | The Perl motto is "There's more than one way to do it." Divining |
303 | how many more is left as an exercise to the reader. |
304 | |
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305 | The three principal virtues of a programmer are Laziness, |
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306 | Impatience, and Hubris. See the Camel Book for why. |
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307 | |