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1=head1 NAME
2
3perl - Practical Extraction and Report Language
4
5=head1 SYNOPSIS
6
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7B<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> ]...>
c07a80fd 17
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18For ease of access, the Perl manual has been split up into a number
19of sections:
20
21 perl Perl overview (this section)
774d564b 22 perldelta Perl changes since previous version
760ac839 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
760ac839 33 perlform Perl formats
5f05dabc 34 perllocale Perl locale support
760ac839 35
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36 perlref Perl references
37 perldsc Perl data structures intro
38 perllol Perl data structures: lists of lists
5f05dabc 39 perltoot Perl OO tutorial
a0d0e21e 40 perlobj Perl objects
cb1a09d0 41 perltie Perl objects hidden behind simple variables
a0d0e21e 42 perlbot Perl OO tricks and examples
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43 perlipc Perl interprocess communication
44
d121ca8c 45 perlbug Perl bug reports howto
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46 perldebug Perl debugging
47 perldiag Perl diagnostic messages
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48 perlsec Perl security
49 perltrap Perl traps for the unwary
50 perlstyle Perl style guide
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51
52 perlpod Perl plain old documentation
53 perlbook Perl book information
54
55 perlembed Perl how to embed perl in your C or C++ app
56 perlapio Perl internal IO abstraction interface
8e07c86e 57 perlxs Perl XS application programming interface
4633a7c4 58 perlxstut Perl XS tutorial
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59 perlguts Perl internal functions for those doing extensions
60 perlcall Perl calling conventions from C
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61
62(If you're intending to read these straight through for the first time,
63the suggested order will tend to reduce the number of forward references.)
64
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65Additional documentation for Perl modules is available in the
66F</usr/local/man/> directory. Some of this is distributed standard with
67Perl, but you'll also find third-party modules there. You should be able
68to view this with your man(1) program by including the proper directories
69in the appropriate start-up files. To find out where these are, type:
16d20bd9 70
760ac839 71 perl -V:man.dir
16d20bd9 72
4633a7c4 73If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
5f05dabc 74you would need to add only F</usr/local/man> to your MANPATH. If
4633a7c4 75they are different, you'll have to add both stems.
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76
77If that doesn't work for some reason, you can still use the
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78supplied F<perldoc> script to view module information. You might
79also look into getting a replacement man program.
16d20bd9 80
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81If something strange has gone wrong with your program and you're not
82sure where you should look for help, try the B<-w> switch first. It
83will often point out exactly where the trouble is.
84
85=head1 DESCRIPTION
86
5f05dabc 87Perl is a language optimized for scanning arbitrary
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88text files, extracting information from those text files, and printing
89reports based on that information. It's also a good language for many
90system management tasks. The language is intended to be practical
91(easy to use, efficient, complete) rather than beautiful (tiny,
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92elegant, minimal).
93
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94Perl combines (in the author's opinion, anyway) some of the best
95features of C, B<sed>, B<awk>, and B<sh>, so people familiar with
96those languages should have little difficulty with it. (Language
97historians will also note some vestiges of B<csh>, Pascal, and even
98BASIC-PLUS.) Expression syntax corresponds quite closely to C
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99expression syntax. Unlike most Unix utilities, Perl does not
100arbitrarily limit the size of your data--if you've got the memory,
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101Perl can slurp in your whole file as a single string. Recursion is of
102unlimited depth. And the tables used by hashes (previously called
103"associative arrays") grow as necessary to prevent degraded
104performance. Perl uses sophisticated pattern matching techniques to
105scan large amounts of data very quickly. Although optimized for
106scanning text, Perl can also deal with binary data, and can make dbm
107files look like hashes. Setuid Perl scripts are safer than C programs
108through a dataflow tracing mechanism which prevents many stupid
109security holes.
110
111If you have a problem that would ordinarily use B<sed> or B<awk> or
112B<sh>, but it exceeds their capabilities or must run a little faster,
113and you don't want to write the silly thing in C, then Perl may be for
114you. There are also translators to turn your B<sed> and B<awk>
115scripts into Perl scripts.
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116
117But wait, there's more...
118
119Perl version 5 is nearly a complete rewrite, and provides
120the following additional benefits:
121
122=over 5
123
124=item * Many usability enhancements
125
126It is now possible to write much more readable Perl code (even within
127regular expressions). Formerly cryptic variable names can be replaced
128by mnemonic identifiers. Error messages are more informative, and the
129optional warnings will catch many of the mistakes a novice might make.
130This cannot be stressed enough. Whenever you get mysterious behavior,
131try the B<-w> switch!!! Whenever you don't get mysterious behavior,
132try using B<-w> anyway.
133
134=item * Simplified grammar
135
136The new yacc grammar is one half the size of the old one. Many of the
137arbitrary grammar rules have been regularized. The number of reserved
138words has been cut by 2/3. Despite this, nearly all old Perl scripts
139will continue to work unchanged.
140
141=item * Lexical scoping
142
143Perl variables may now be declared within a lexical scope, like "auto"
144variables in C. Not only is this more efficient, but it contributes
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145to better privacy for "programming in the large". Anonymous
146subroutines exhibit deep binding of lexical variables (closures).
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147
148=item * Arbitrarily nested data structures
149
150Any scalar value, including any array element, may now contain a
151reference to any other variable or subroutine. You can easily create
152anonymous variables and subroutines. Perl manages your reference
153counts for you.
154
155=item * Modularity and reusability
156
157The Perl library is now defined in terms of modules which can be easily
158shared among various packages. A package may choose to import all or a
159portion of a module's published interface. Pragmas (that is, compiler
160directives) are defined and used by the same mechanism.
161
162=item * Object-oriented programming
163
164A package can function as a class. Dynamic multiple inheritance and
165virtual methods are supported in a straightforward manner and with very
166little new syntax. Filehandles may now be treated as objects.
167
c07a80fd 168=item * Embeddable and Extensible
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169
170Perl may now be embedded easily in your C or C++ application, and can
171either call or be called by your routines through a documented
172interface. The XS preprocessor is provided to make it easy to glue
173your C or C++ routines into Perl. Dynamic loading of modules is
5f05dabc 174supported, and Perl itself can be made into a dynamic library.
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175
176=item * POSIX compliant
177
178A major new module is the POSIX module, which provides access to all
179available POSIX routines and definitions, via object classes where
180appropriate.
181
182=item * Package constructors and destructors
183
184The new BEGIN and END blocks provide means to capture control as
185a package is being compiled, and after the program exits. As a
186degenerate case they work just like awk's BEGIN and END when you
187use the B<-p> or B<-n> switches.
188
189=item * Multiple simultaneous DBM implementations
190
191A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
192files from the same script simultaneously. In fact, the old dbmopen
193interface has been generalized to allow any variable to be tied
194to an object class which defines its access methods.
195
196=item * Subroutine definitions may now be autoloaded
197
198In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
5f05dabc 199semantics for undefined subroutine calls. It's not for just autoloading.
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200
201=item * Regular expression enhancements
202
203You can now specify non-greedy quantifiers. You can now do grouping
204without creating a backreference. You can now write regular expressions
205with embedded whitespace and comments for readability. A consistent
206extensibility mechanism has been added that is upwardly compatible with
207all old regular expressions.
208
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209=item * Innumerable Unbundled Modules
210
211The Comprehensive Perl Archive Network described in L<perlmod>
212contains hundreds of plug-and-play modules full of reusable
213code. See F<http://www.perl.com/CPAN> for a site near you.
214
215=item * Compilability
216
217While not yet in full production mode, a working perl-to-C compiler
218does exist. It can generate portable bytecode, simple C, or
219optimized C code.
220
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221=back
222
223Ok, that's I<definitely> enough hype.
224
225=head1 ENVIRONMENT
226
227=over 12
228
229=item HOME
230
231Used if chdir has no argument.
232
233=item LOGDIR
234
235Used if chdir has no argument and HOME is not set.
236
237=item PATH
238
239Used in executing subprocesses, and in finding the script if B<-S> is
240used.
241
242=item PERL5LIB
243
244A colon-separated list of directories in which to look for Perl library
245files before looking in the standard library and the current
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246directory. If PERL5LIB is not defined, PERLLIB is used. When running
247taint checks (because the script was running setuid or setgid, or the
248B<-T> switch was used), neither variable is used. The script should
249instead say
250
251 use lib "/my/directory";
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252
253=item PERL5DB
254
255The command used to get the debugger code. If unset, uses
256
257 BEGIN { require 'perl5db.pl' }
258
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259=item PERL_DESTRUCT_LEVEL
260
261Relevant only if your perl executable was built with B<-DDEBUGGING>,
262this controls the behavior of global destruction of objects and other
263references.
264
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265=item PERLLIB
266
267A colon-separated list of directories in which to look for Perl library
268files before looking in the standard library and the current
269directory. If PERL5LIB is defined, PERLLIB is not used.
270
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271=back
272
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273Perl also has environment variables that control how Perl handles data
274specific to particular natural languages. See L<perllocale>.
fb252e81 275
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276Apart from these, Perl uses no other environment variables, except
277to make them available to the script being executed, and to child
278processes. However, scripts running setuid would do well to execute
279the following lines before doing anything else, just to keep people
280honest:
281
282 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
283 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
284 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
285
286=head1 AUTHOR
287
fb252e81 288Larry Wall E<lt>F<larry@wall.org>E<gt>, with the help of oodles of other folks.
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289
290=head1 FILES
291
292 "/tmp/perl-e$$" temporary file for -e commands
5f05dabc 293 "@INC" locations of perl libraries
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294
295=head1 SEE ALSO
296
297 a2p awk to perl translator
4633a7c4 298
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299 s2p sed to perl translator
300
301=head1 DIAGNOSTICS
302
303The B<-w> switch produces some lovely diagnostics.
304
305See L<perldiag> for explanations of all Perl's diagnostics.
306
307Compilation errors will tell you the line number of the error, with an
308indication of the next token or token type that was to be examined.
309(In the case of a script passed to Perl via B<-e> switches, each
310B<-e> is counted as one line.)
311
312Setuid scripts have additional constraints that can produce error
313messages such as "Insecure dependency". See L<perlsec>.
314
315Did we mention that you should definitely consider using the B<-w>
316switch?
317
318=head1 BUGS
319
320The B<-w> switch is not mandatory.
321
322Perl is at the mercy of your machine's definitions of various
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323operations such as type casting, atof(), and sprintf(). The latter
324can even trigger a core dump when passed ludicrous input values.
a0d0e21e 325
748a9306 326If your stdio requires a seek or eof between reads and writes on a
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327particular stream, so does Perl. (This doesn't apply to sysread()
328and syswrite().)
329
330While none of the built-in data types have any arbitrary size limits
331(apart from memory size), there are still a few arbitrary limits: a
d357d931 332given variable name may not be longer than 255 characters, and no
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333component of your PATH may be longer than 255 if you use B<-S>. A regular
334expression may not compile to more than 32767 bytes internally.
335
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336You may mail your bug reports (be sure to include full configuration
337information as output by the myconfig program in the perl source tree,
338or by C<perl -V>) to F<perlbug@perl.com>.
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339If you've succeeded in compiling perl, the perlbug script in the utils/
340subdirectory can be used to help mail in a bug report.
4633a7c4 341
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342Perl actually stands for Pathologically Eclectic Rubbish Lister, but
343don't tell anyone I said that.
344
345=head1 NOTES
346
347The Perl motto is "There's more than one way to do it." Divining
348how many more is left as an exercise to the reader.
349
4633a7c4 350The three principal virtues of a programmer are Laziness,
a0d0e21e 351Impatience, and Hubris. See the Camel Book for why.
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