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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)
cb1a09d0 22 perltoc Perl documentation table of contents
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
fb252e81 34 perli18n Perl internalization
760ac839 35
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36 perlref Perl references
37 perldsc Perl data structures intro
38 perllol Perl data structures: lists of lists
a0d0e21e 39 perlobj Perl objects
cb1a09d0 40 perltie Perl objects hidden behind simple variables
a0d0e21e 41 perlbot Perl OO tricks and examples
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42 perlipc Perl interprocess communication
43
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44 perldebug Perl debugging
45 perldiag Perl diagnostic messages
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46 perlsec Perl security
47 perltrap Perl traps for the unwary
48 perlstyle Perl style guide
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49
50 perlpod Perl plain old documentation
51 perlbook Perl book information
52
53 perlembed Perl how to embed perl in your C or C++ app
54 perlapio Perl internal IO abstraction interface
8e07c86e 55 perlxs Perl XS application programming interface
4633a7c4 56 perlxstut Perl XS tutorial
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57 perlguts Perl internal functions for those doing extensions
58 perlcall Perl calling conventions from C
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59
60(If you're intending to read these straight through for the first time,
61the suggested order will tend to reduce the number of forward references.)
62
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63Additional documentation for Perl modules is available in the
64F</usr/local/man/> directory. Some of this is distributed standard with
65Perl, but you'll also find third-party modules there. You should be able
66to view this with your man(1) program by including the proper directories
67in the appropriate start-up files. To find out where these are, type:
16d20bd9 68
760ac839 69 perl -V:man.dir
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71If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
72you would only need to add F</usr/local/man> to your MANPATH. If
73they are different, you'll have to add both stems.
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74
75If that doesn't work for some reason, you can still use the
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76supplied F<perldoc> script to view module information. You might
77also look into getting a replacement man program.
16d20bd9 78
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79If something strange has gone wrong with your program and you're not
80sure where you should look for help, try the B<-w> switch first. It
81will often point out exactly where the trouble is.
82
83=head1 DESCRIPTION
84
85Perl is an interpreted language optimized for scanning arbitrary
86text files, extracting information from those text files, and printing
87reports based on that information. It's also a good language for many
88system management tasks. The language is intended to be practical
89(easy to use, efficient, complete) rather than beautiful (tiny,
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90elegant, minimal).
91
92Perl combines (in the author's opinion, anyway) some
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93of the best features of C, B<sed>, B<awk>, and B<sh>, so people
94familiar with those languages should have little difficulty with it.
95(Language historians will also note some vestiges of B<csh>, Pascal,
96and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
97expression syntax. Unlike most Unix utilities, Perl does not
98arbitrarily limit the size of your data--if you've got the memory,
99Perl can slurp in your whole file as a single string. Recursion is
100of unlimited depth. And the hash tables used by associative arrays
101grow as necessary to prevent degraded performance. Perl uses
102sophisticated pattern matching techniques to scan large amounts of data
103very quickly. Although optimized for scanning text, Perl can also
104deal with binary data, and can make dbm files look like associative
c07a80fd 105arrays. Setuid Perl scripts are safer than
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106C programs through a dataflow tracing mechanism which prevents many
107stupid security holes. If you have a problem that would ordinarily use
108B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
109run a little faster, and you don't want to write the silly thing in C,
110then Perl may be for you. There are also translators to turn your
111B<sed> and B<awk> scripts into Perl scripts.
112
113But wait, there's more...
114
115Perl version 5 is nearly a complete rewrite, and provides
116the following additional benefits:
117
118=over 5
119
120=item * Many usability enhancements
121
122It is now possible to write much more readable Perl code (even within
123regular expressions). Formerly cryptic variable names can be replaced
124by mnemonic identifiers. Error messages are more informative, and the
125optional warnings will catch many of the mistakes a novice might make.
126This cannot be stressed enough. Whenever you get mysterious behavior,
127try the B<-w> switch!!! Whenever you don't get mysterious behavior,
128try using B<-w> anyway.
129
130=item * Simplified grammar
131
132The new yacc grammar is one half the size of the old one. Many of the
133arbitrary grammar rules have been regularized. The number of reserved
134words has been cut by 2/3. Despite this, nearly all old Perl scripts
135will continue to work unchanged.
136
137=item * Lexical scoping
138
139Perl variables may now be declared within a lexical scope, like "auto"
140variables in C. Not only is this more efficient, but it contributes
141to better privacy for "programming in the large".
142
143=item * Arbitrarily nested data structures
144
145Any scalar value, including any array element, may now contain a
146reference to any other variable or subroutine. You can easily create
147anonymous variables and subroutines. Perl manages your reference
148counts for you.
149
150=item * Modularity and reusability
151
152The Perl library is now defined in terms of modules which can be easily
153shared among various packages. A package may choose to import all or a
154portion of a module's published interface. Pragmas (that is, compiler
155directives) are defined and used by the same mechanism.
156
157=item * Object-oriented programming
158
159A package can function as a class. Dynamic multiple inheritance and
160virtual methods are supported in a straightforward manner and with very
161little new syntax. Filehandles may now be treated as objects.
162
c07a80fd 163=item * Embeddable and Extensible
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164
165Perl may now be embedded easily in your C or C++ application, and can
166either call or be called by your routines through a documented
167interface. The XS preprocessor is provided to make it easy to glue
168your C or C++ routines into Perl. Dynamic loading of modules is
169supported.
170
171=item * POSIX compliant
172
173A major new module is the POSIX module, which provides access to all
174available POSIX routines and definitions, via object classes where
175appropriate.
176
177=item * Package constructors and destructors
178
179The new BEGIN and END blocks provide means to capture control as
180a package is being compiled, and after the program exits. As a
181degenerate case they work just like awk's BEGIN and END when you
182use the B<-p> or B<-n> switches.
183
184=item * Multiple simultaneous DBM implementations
185
186A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
187files from the same script simultaneously. In fact, the old dbmopen
188interface has been generalized to allow any variable to be tied
189to an object class which defines its access methods.
190
191=item * Subroutine definitions may now be autoloaded
192
193In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
194semantics for undefined subroutine calls. It's not just for autoloading.
195
196=item * Regular expression enhancements
197
198You can now specify non-greedy quantifiers. You can now do grouping
199without creating a backreference. You can now write regular expressions
200with embedded whitespace and comments for readability. A consistent
201extensibility mechanism has been added that is upwardly compatible with
202all old regular expressions.
203
204=back
205
206Ok, that's I<definitely> enough hype.
207
208=head1 ENVIRONMENT
209
210=over 12
211
212=item HOME
213
214Used if chdir has no argument.
215
216=item LOGDIR
217
218Used if chdir has no argument and HOME is not set.
219
220=item PATH
221
222Used in executing subprocesses, and in finding the script if B<-S> is
223used.
224
225=item PERL5LIB
226
227A colon-separated list of directories in which to look for Perl library
228files before looking in the standard library and the current
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229directory. If PERL5LIB is not defined, PERLLIB is used. When running
230taint checks (because the script was running setuid or setgid, or the
231B<-T> switch was used), neither variable is used. The script should
232instead say
233
234 use lib "/my/directory";
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235
236=item PERL5DB
237
238The command used to get the debugger code. If unset, uses
239
240 BEGIN { require 'perl5db.pl' }
241
242=item PERLLIB
243
244A colon-separated list of directories in which to look for Perl library
245files before looking in the standard library and the current
246directory. If PERL5LIB is defined, PERLLIB is not used.
247
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248=back
249
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250Perl also has environment variables that control how Perl handles
251language-specific data. Please consult the L<perli18n> section.
252
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253Apart from these, Perl uses no other environment variables, except
254to make them available to the script being executed, and to child
255processes. However, scripts running setuid would do well to execute
256the following lines before doing anything else, just to keep people
257honest:
258
259 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
260 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
261 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
262
263=head1 AUTHOR
264
fb252e81 265Larry Wall E<lt>F<larry@wall.org>E<gt>, with the help of oodles of other folks.
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266
267=head1 FILES
268
269 "/tmp/perl-e$$" temporary file for -e commands
270 "@INC" locations of perl 5 libraries
271
272=head1 SEE ALSO
273
274 a2p awk to perl translator
4633a7c4 275
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276 s2p sed to perl translator
277
278=head1 DIAGNOSTICS
279
280The B<-w> switch produces some lovely diagnostics.
281
282See L<perldiag> for explanations of all Perl's diagnostics.
283
284Compilation errors will tell you the line number of the error, with an
285indication of the next token or token type that was to be examined.
286(In the case of a script passed to Perl via B<-e> switches, each
287B<-e> is counted as one line.)
288
289Setuid scripts have additional constraints that can produce error
290messages such as "Insecure dependency". See L<perlsec>.
291
292Did we mention that you should definitely consider using the B<-w>
293switch?
294
295=head1 BUGS
296
297The B<-w> switch is not mandatory.
298
299Perl is at the mercy of your machine's definitions of various
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300operations such as type casting, atof() and sprintf(). The latter
301can even trigger a coredump when passed ludicrous input values.
a0d0e21e 302
748a9306 303If your stdio requires a seek or eof between reads and writes on a
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304particular stream, so does Perl. (This doesn't apply to sysread()
305and syswrite().)
306
307While none of the built-in data types have any arbitrary size limits
308(apart from memory size), there are still a few arbitrary limits: a
d357d931 309given variable name may not be longer than 255 characters, and no
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310component of your PATH may be longer than 255 if you use B<-S>. A regular
311expression may not compile to more than 32767 bytes internally.
312
fb252e81 313See the perl bugs database at F<http://perl.com/perl/bugs/>. You may
cb1a09d0 314mail your bug reports (be sure to include full configuration information
fb252e81 315as output by the myconfig program in the perl source tree, or by C<perl -V>) to
cb1a09d0 316F<perlbug@perl.com>.
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317If you've succeeded in compiling perl, the perlbug script in the utils/
318subdirectory can be used to help mail in a bug report.
4633a7c4 319
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320Perl actually stands for Pathologically Eclectic Rubbish Lister, but
321don't tell anyone I said that.
322
323=head1 NOTES
324
325The Perl motto is "There's more than one way to do it." Divining
326how many more is left as an exercise to the reader.
327
4633a7c4 328The three principal virtues of a programmer are Laziness,
a0d0e21e 329Impatience, and Hubris. See the Camel Book for why.
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