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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 | |
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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 | |
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93 | Perl combines (in the author's opinion, anyway) some of the best |
94 | features of C, B<sed>, B<awk>, and B<sh>, so people familiar with |
95 | those languages should have little difficulty with it. (Language |
96 | historians will also note some vestiges of B<csh>, Pascal, and even |
97 | BASIC-PLUS.) Expression syntax corresponds quite closely to C |
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98 | expression syntax. Unlike most Unix utilities, Perl does not |
99 | arbitrarily limit the size of your data--if you've got the memory, |
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100 | Perl can slurp in your whole file as a single string. Recursion is of |
101 | unlimited depth. And the tables used by hashes (previously called |
102 | "associative arrays") grow as necessary to prevent degraded |
103 | performance. Perl uses sophisticated pattern matching techniques to |
104 | scan large amounts of data very quickly. Although optimized for |
105 | scanning text, Perl can also deal with binary data, and can make dbm |
106 | files look like hashes. Setuid Perl scripts are safer than C programs |
107 | through a dataflow tracing mechanism which prevents many stupid |
108 | security holes. |
109 | |
110 | If you have a problem that would ordinarily use B<sed> or B<awk> or |
111 | B<sh>, but it exceeds their capabilities or must run a little faster, |
112 | and you don't want to write the silly thing in C, then Perl may be for |
113 | you. There are also translators to turn your B<sed> and B<awk> |
114 | scripts into Perl scripts. |
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115 | |
116 | But wait, there's more... |
117 | |
118 | Perl version 5 is nearly a complete rewrite, and provides |
119 | the following additional benefits: |
120 | |
121 | =over 5 |
122 | |
123 | =item * Many usability enhancements |
124 | |
125 | It is now possible to write much more readable Perl code (even within |
126 | regular expressions). Formerly cryptic variable names can be replaced |
127 | by mnemonic identifiers. Error messages are more informative, and the |
128 | optional warnings will catch many of the mistakes a novice might make. |
129 | This cannot be stressed enough. Whenever you get mysterious behavior, |
130 | try the B<-w> switch!!! Whenever you don't get mysterious behavior, |
131 | try using B<-w> anyway. |
132 | |
133 | =item * Simplified grammar |
134 | |
135 | The new yacc grammar is one half the size of the old one. Many of the |
136 | arbitrary grammar rules have been regularized. The number of reserved |
137 | words has been cut by 2/3. Despite this, nearly all old Perl scripts |
138 | will continue to work unchanged. |
139 | |
140 | =item * Lexical scoping |
141 | |
142 | Perl variables may now be declared within a lexical scope, like "auto" |
143 | variables in C. Not only is this more efficient, but it contributes |
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144 | to better privacy for "programming in the large". Anonymous |
145 | subroutines exhibit deep binding of lexical variables (closures). |
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146 | |
147 | =item * Arbitrarily nested data structures |
148 | |
149 | Any scalar value, including any array element, may now contain a |
150 | reference to any other variable or subroutine. You can easily create |
151 | anonymous variables and subroutines. Perl manages your reference |
152 | counts for you. |
153 | |
154 | =item * Modularity and reusability |
155 | |
156 | The Perl library is now defined in terms of modules which can be easily |
157 | shared among various packages. A package may choose to import all or a |
158 | portion of a module's published interface. Pragmas (that is, compiler |
159 | directives) are defined and used by the same mechanism. |
160 | |
161 | =item * Object-oriented programming |
162 | |
163 | A package can function as a class. Dynamic multiple inheritance and |
164 | virtual methods are supported in a straightforward manner and with very |
165 | little new syntax. Filehandles may now be treated as objects. |
166 | |
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167 | =item * Embeddable and Extensible |
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168 | |
169 | Perl may now be embedded easily in your C or C++ application, and can |
170 | either call or be called by your routines through a documented |
171 | interface. The XS preprocessor is provided to make it easy to glue |
172 | your C or C++ routines into Perl. Dynamic loading of modules is |
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173 | supported, and Perl itself can be made into a dynamic library. |
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174 | |
175 | =item * POSIX compliant |
176 | |
177 | A major new module is the POSIX module, which provides access to all |
178 | available POSIX routines and definitions, via object classes where |
179 | appropriate. |
180 | |
181 | =item * Package constructors and destructors |
182 | |
183 | The new BEGIN and END blocks provide means to capture control as |
184 | a package is being compiled, and after the program exits. As a |
185 | degenerate case they work just like awk's BEGIN and END when you |
186 | use the B<-p> or B<-n> switches. |
187 | |
188 | =item * Multiple simultaneous DBM implementations |
189 | |
190 | A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB |
191 | files from the same script simultaneously. In fact, the old dbmopen |
192 | interface has been generalized to allow any variable to be tied |
193 | to an object class which defines its access methods. |
194 | |
195 | =item * Subroutine definitions may now be autoloaded |
196 | |
197 | In fact, the AUTOLOAD mechanism also allows you to define any arbitrary |
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198 | semantics for undefined subroutine calls. It's not for just autoloading. |
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199 | |
200 | =item * Regular expression enhancements |
201 | |
202 | You can now specify non-greedy quantifiers. You can now do grouping |
203 | without creating a backreference. You can now write regular expressions |
204 | with embedded whitespace and comments for readability. A consistent |
205 | extensibility mechanism has been added that is upwardly compatible with |
206 | all old regular expressions. |
207 | |
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208 | =item * Innumerable Unbundled Modules |
209 | |
210 | The Comprehensive Perl Archive Network described in L<perlmod> |
211 | contains hundreds of plug-and-play modules full of reusable |
212 | code. See F<http://www.perl.com/CPAN> for a site near you. |
213 | |
214 | =item * Compilability |
215 | |
216 | While not yet in full production mode, a working perl-to-C compiler |
217 | does exist. It can generate portable bytecode, simple C, or |
218 | optimized C code. |
219 | |
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220 | =back |
221 | |
222 | Ok, that's I<definitely> enough hype. |
223 | |
224 | =head1 ENVIRONMENT |
225 | |
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226 | See L<perlrun>. |
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227 | |
228 | =head1 AUTHOR |
229 | |
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230 | Larry Wall <F<larry@wall.org>>, with the help of oodles of other folks. |
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231 | |
232 | =head1 FILES |
233 | |
234 | "/tmp/perl-e$$" temporary file for -e commands |
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235 | "@INC" locations of perl libraries |
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236 | |
237 | =head1 SEE ALSO |
238 | |
239 | a2p awk to perl translator |
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240 | |
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241 | s2p sed to perl translator |
242 | |
243 | =head1 DIAGNOSTICS |
244 | |
245 | The B<-w> switch produces some lovely diagnostics. |
246 | |
247 | See L<perldiag> for explanations of all Perl's diagnostics. |
248 | |
249 | Compilation errors will tell you the line number of the error, with an |
250 | indication of the next token or token type that was to be examined. |
251 | (In the case of a script passed to Perl via B<-e> switches, each |
252 | B<-e> is counted as one line.) |
253 | |
254 | Setuid scripts have additional constraints that can produce error |
255 | messages such as "Insecure dependency". See L<perlsec>. |
256 | |
257 | Did we mention that you should definitely consider using the B<-w> |
258 | switch? |
259 | |
260 | =head1 BUGS |
261 | |
262 | The B<-w> switch is not mandatory. |
263 | |
264 | Perl is at the mercy of your machine's definitions of various |
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265 | operations such as type casting, atof(), and sprintf(). The latter |
266 | can even trigger a core dump when passed ludicrous input values. |
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267 | |
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268 | If your stdio requires a seek or eof between reads and writes on a |
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269 | particular stream, so does Perl. (This doesn't apply to sysread() |
270 | and syswrite().) |
271 | |
272 | While none of the built-in data types have any arbitrary size limits |
273 | (apart from memory size), there are still a few arbitrary limits: a |
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274 | given variable name may not be longer than 255 characters, and no |
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275 | component of your PATH may be longer than 255 if you use B<-S>. A regular |
276 | expression may not compile to more than 32767 bytes internally. |
277 | |
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278 | You may mail your bug reports (be sure to include full configuration |
279 | information as output by the myconfig program in the perl source tree, |
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280 | or by C<perl -V>) to <F<perlbug@perl.com>>. |
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281 | If you've succeeded in compiling perl, the perlbug script in the utils/ |
282 | subdirectory can be used to help mail in a bug report. |
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283 | |
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284 | Perl actually stands for Pathologically Eclectic Rubbish Lister, but |
285 | don't tell anyone I said that. |
286 | |
287 | =head1 NOTES |
288 | |
289 | The Perl motto is "There's more than one way to do it." Divining |
290 | how many more is left as an exercise to the reader. |
291 | |
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292 | The three principal virtues of a programmer are Laziness, |
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293 | Impatience, and Hubris. See the Camel Book for why. |
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294 | |