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1 | =head1 NAME |
2 | |
3 | perl - Practical Extraction and Report Language |
4 | |
5 | =head1 SYNOPSIS |
6 | |
7 | For ease of access, the Perl manual has been split up into a number |
8 | of sections: |
9 | |
10 | perl Perl overview (this section) |
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11 | perltoc Perl documentation table of contents |
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12 | perldata Perl data structures |
13 | perlsyn Perl syntax |
14 | perlop Perl operators and precedence |
15 | perlre Perl regular expressions |
16 | perlrun Perl execution and options |
17 | perlfunc Perl builtin functions |
18 | perlvar Perl predefined variables |
19 | perlsub Perl subroutines |
20 | perlmod Perl modules |
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21 | perlref Perl references |
22 | perldsc Perl data structures intro |
23 | perllol Perl data structures: lists of lists |
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24 | perlobj Perl objects |
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25 | perltie Perl objects hidden behind simple variables |
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26 | perlbot Perl OO tricks and examples |
27 | perldebug Perl debugging |
28 | perldiag Perl diagnostic messages |
29 | perlform Perl formats |
30 | perlipc Perl interprocess communication |
31 | perlsec Perl security |
32 | perltrap Perl traps for the unwary |
33 | perlstyle Perl style guide |
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34 | perlxs Perl XS application programming interface |
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35 | perlxstut Perl XS tutorial |
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36 | perlguts Perl internal functions for those doing extensions |
37 | perlcall Perl calling conventions from C |
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38 | perlembed Perl how to embed perl in your C or C++ app |
39 | perlpod Perl plain old documentation |
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40 | perlbook Perl book information |
41 | |
42 | (If you're intending to read these straight through for the first time, |
43 | the suggested order will tend to reduce the number of forward references.) |
44 | |
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45 | Additional documentation for Perl modules is available in the |
46 | F</usr/local/man/> directory. Some of this is distributed standard with |
47 | Perl, but you'll also find third-party modules there. You should be able |
48 | to view this with your man(1) program by including the proper directories |
49 | in the appropriate start-up files. To find out where these are, type: |
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50 | |
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51 | perl -le 'use Config; print "@Config{man1dir,man3dir}"' |
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52 | |
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53 | If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>, |
54 | you would only need to add F</usr/local/man> to your MANPATH. If |
55 | they are different, you'll have to add both stems. |
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56 | |
57 | If that doesn't work for some reason, you can still use the |
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58 | supplied F<perldoc> script to view module information. You might |
59 | also look into getting a replacement man program. |
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60 | |
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61 | If something strange has gone wrong with your program and you're not |
62 | sure where you should look for help, try the B<-w> switch first. It |
63 | will often point out exactly where the trouble is. |
64 | |
65 | =head1 DESCRIPTION |
66 | |
67 | Perl is an interpreted language optimized for scanning arbitrary |
68 | text files, extracting information from those text files, and printing |
69 | reports based on that information. It's also a good language for many |
70 | system management tasks. The language is intended to be practical |
71 | (easy to use, efficient, complete) rather than beautiful (tiny, |
72 | elegant, minimal). It combines (in the author's opinion, anyway) some |
73 | of the best features of C, B<sed>, B<awk>, and B<sh>, so people |
74 | familiar with those languages should have little difficulty with it. |
75 | (Language historians will also note some vestiges of B<csh>, Pascal, |
76 | and even BASIC-PLUS.) Expression syntax corresponds quite closely to C |
77 | expression syntax. Unlike most Unix utilities, Perl does not |
78 | arbitrarily limit the size of your data--if you've got the memory, |
79 | Perl can slurp in your whole file as a single string. Recursion is |
80 | of unlimited depth. And the hash tables used by associative arrays |
81 | grow as necessary to prevent degraded performance. Perl uses |
82 | sophisticated pattern matching techniques to scan large amounts of data |
83 | very quickly. Although optimized for scanning text, Perl can also |
84 | deal with binary data, and can make dbm files look like associative |
85 | arrays (where dbm is available). Setuid Perl scripts are safer than |
86 | C programs through a dataflow tracing mechanism which prevents many |
87 | stupid security holes. If you have a problem that would ordinarily use |
88 | B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must |
89 | run a little faster, and you don't want to write the silly thing in C, |
90 | then Perl may be for you. There are also translators to turn your |
91 | B<sed> and B<awk> scripts into Perl scripts. |
92 | |
93 | But wait, there's more... |
94 | |
95 | Perl version 5 is nearly a complete rewrite, and provides |
96 | the following additional benefits: |
97 | |
98 | =over 5 |
99 | |
100 | =item * Many usability enhancements |
101 | |
102 | It is now possible to write much more readable Perl code (even within |
103 | regular expressions). Formerly cryptic variable names can be replaced |
104 | by mnemonic identifiers. Error messages are more informative, and the |
105 | optional warnings will catch many of the mistakes a novice might make. |
106 | This cannot be stressed enough. Whenever you get mysterious behavior, |
107 | try the B<-w> switch!!! Whenever you don't get mysterious behavior, |
108 | try using B<-w> anyway. |
109 | |
110 | =item * Simplified grammar |
111 | |
112 | The new yacc grammar is one half the size of the old one. Many of the |
113 | arbitrary grammar rules have been regularized. The number of reserved |
114 | words has been cut by 2/3. Despite this, nearly all old Perl scripts |
115 | will continue to work unchanged. |
116 | |
117 | =item * Lexical scoping |
118 | |
119 | Perl variables may now be declared within a lexical scope, like "auto" |
120 | variables in C. Not only is this more efficient, but it contributes |
121 | to better privacy for "programming in the large". |
122 | |
123 | =item * Arbitrarily nested data structures |
124 | |
125 | Any scalar value, including any array element, may now contain a |
126 | reference to any other variable or subroutine. You can easily create |
127 | anonymous variables and subroutines. Perl manages your reference |
128 | counts for you. |
129 | |
130 | =item * Modularity and reusability |
131 | |
132 | The Perl library is now defined in terms of modules which can be easily |
133 | shared among various packages. A package may choose to import all or a |
134 | portion of a module's published interface. Pragmas (that is, compiler |
135 | directives) are defined and used by the same mechanism. |
136 | |
137 | =item * Object-oriented programming |
138 | |
139 | A package can function as a class. Dynamic multiple inheritance and |
140 | virtual methods are supported in a straightforward manner and with very |
141 | little new syntax. Filehandles may now be treated as objects. |
142 | |
143 | =item * Embeddible and Extensible |
144 | |
145 | Perl may now be embedded easily in your C or C++ application, and can |
146 | either call or be called by your routines through a documented |
147 | interface. The XS preprocessor is provided to make it easy to glue |
148 | your C or C++ routines into Perl. Dynamic loading of modules is |
149 | supported. |
150 | |
151 | =item * POSIX compliant |
152 | |
153 | A major new module is the POSIX module, which provides access to all |
154 | available POSIX routines and definitions, via object classes where |
155 | appropriate. |
156 | |
157 | =item * Package constructors and destructors |
158 | |
159 | The new BEGIN and END blocks provide means to capture control as |
160 | a package is being compiled, and after the program exits. As a |
161 | degenerate case they work just like awk's BEGIN and END when you |
162 | use the B<-p> or B<-n> switches. |
163 | |
164 | =item * Multiple simultaneous DBM implementations |
165 | |
166 | A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB |
167 | files from the same script simultaneously. In fact, the old dbmopen |
168 | interface has been generalized to allow any variable to be tied |
169 | to an object class which defines its access methods. |
170 | |
171 | =item * Subroutine definitions may now be autoloaded |
172 | |
173 | In fact, the AUTOLOAD mechanism also allows you to define any arbitrary |
174 | semantics for undefined subroutine calls. It's not just for autoloading. |
175 | |
176 | =item * Regular expression enhancements |
177 | |
178 | You can now specify non-greedy quantifiers. You can now do grouping |
179 | without creating a backreference. You can now write regular expressions |
180 | with embedded whitespace and comments for readability. A consistent |
181 | extensibility mechanism has been added that is upwardly compatible with |
182 | all old regular expressions. |
183 | |
184 | =back |
185 | |
186 | Ok, that's I<definitely> enough hype. |
187 | |
188 | =head1 ENVIRONMENT |
189 | |
190 | =over 12 |
191 | |
192 | =item HOME |
193 | |
194 | Used if chdir has no argument. |
195 | |
196 | =item LOGDIR |
197 | |
198 | Used if chdir has no argument and HOME is not set. |
199 | |
200 | =item PATH |
201 | |
202 | Used in executing subprocesses, and in finding the script if B<-S> is |
203 | used. |
204 | |
205 | =item PERL5LIB |
206 | |
207 | A colon-separated list of directories in which to look for Perl library |
208 | files before looking in the standard library and the current |
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209 | directory. If PERL5LIB is not defined, PERLLIB is used. When running |
210 | taint checks (because the script was running setuid or setgid, or the |
211 | B<-T> switch was used), neither variable is used. The script should |
212 | instead say |
213 | |
214 | use lib "/my/directory"; |
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215 | |
216 | =item PERL5DB |
217 | |
218 | The command used to get the debugger code. If unset, uses |
219 | |
220 | BEGIN { require 'perl5db.pl' } |
221 | |
222 | =item PERLLIB |
223 | |
224 | A colon-separated list of directories in which to look for Perl library |
225 | files before looking in the standard library and the current |
226 | directory. If PERL5LIB is defined, PERLLIB is not used. |
227 | |
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228 | =back |
229 | |
230 | Apart from these, Perl uses no other environment variables, except |
231 | to make them available to the script being executed, and to child |
232 | processes. However, scripts running setuid would do well to execute |
233 | the following lines before doing anything else, just to keep people |
234 | honest: |
235 | |
236 | $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need |
237 | $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'}; |
238 | $ENV{'IFS'} = '' if defined $ENV{'IFS'}; |
239 | |
240 | =head1 AUTHOR |
241 | |
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242 | Larry Wall E<lt><F<lwall@netlabs.com>E<gt>, with the help of oodles of other folks. |
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243 | |
244 | =head1 FILES |
245 | |
246 | "/tmp/perl-e$$" temporary file for -e commands |
247 | "@INC" locations of perl 5 libraries |
248 | |
249 | =head1 SEE ALSO |
250 | |
251 | a2p awk to perl translator |
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252 | |
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253 | s2p sed to perl translator |
254 | |
255 | =head1 DIAGNOSTICS |
256 | |
257 | The B<-w> switch produces some lovely diagnostics. |
258 | |
259 | See L<perldiag> for explanations of all Perl's diagnostics. |
260 | |
261 | Compilation errors will tell you the line number of the error, with an |
262 | indication of the next token or token type that was to be examined. |
263 | (In the case of a script passed to Perl via B<-e> switches, each |
264 | B<-e> is counted as one line.) |
265 | |
266 | Setuid scripts have additional constraints that can produce error |
267 | messages such as "Insecure dependency". See L<perlsec>. |
268 | |
269 | Did we mention that you should definitely consider using the B<-w> |
270 | switch? |
271 | |
272 | =head1 BUGS |
273 | |
274 | The B<-w> switch is not mandatory. |
275 | |
276 | Perl is at the mercy of your machine's definitions of various |
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277 | operations such as type casting, atof() and sprintf(). The latter |
278 | can even trigger a coredump when passed ludicrous input values. |
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279 | |
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280 | If your stdio requires a seek or eof between reads and writes on a |
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281 | particular stream, so does Perl. (This doesn't apply to sysread() |
282 | and syswrite().) |
283 | |
284 | While none of the built-in data types have any arbitrary size limits |
285 | (apart from memory size), there are still a few arbitrary limits: a |
286 | given identifier may not be longer than 255 characters, and no |
287 | component of your PATH may be longer than 255 if you use B<-S>. A regular |
288 | expression may not compile to more than 32767 bytes internally. |
289 | |
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290 | See the perl bugs database at F<http://perl.com/perl/bugs/>. You may |
291 | mail your bug reports (be sure to include full configuration information |
292 | as output by the myconfig program in the perl source tree) to |
293 | F<perlbug@perl.com>. |
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294 | |
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295 | Perl actually stands for Pathologically Eclectic Rubbish Lister, but |
296 | don't tell anyone I said that. |
297 | |
298 | =head1 NOTES |
299 | |
300 | The Perl motto is "There's more than one way to do it." Divining |
301 | how many more is left as an exercise to the reader. |
302 | |
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303 | The three principal virtues of a programmer are Laziness, |
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304 | Impatience, and Hubris. See the Camel Book for why. |
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305 | |