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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
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33 perlform Perl formats
34
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35 perlref Perl references
36 perldsc Perl data structures intro
37 perllol Perl data structures: lists of lists
a0d0e21e 38 perlobj Perl objects
cb1a09d0 39 perltie Perl objects hidden behind simple variables
a0d0e21e 40 perlbot Perl OO tricks and examples
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41 perlipc Perl interprocess communication
42
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43 perldebug Perl debugging
44 perldiag Perl diagnostic messages
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45 perlsec Perl security
46 perltrap Perl traps for the unwary
47 perlstyle Perl style guide
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48
49 perlpod Perl plain old documentation
50 perlbook Perl book information
51
52 perlembed Perl how to embed perl in your C or C++ app
53 perlapio Perl internal IO abstraction interface
8e07c86e 54 perlxs Perl XS application programming interface
4633a7c4 55 perlxstut Perl XS tutorial
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56 perlguts Perl internal functions for those doing extensions
57 perlcall Perl calling conventions from C
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58
59(If you're intending to read these straight through for the first time,
60the suggested order will tend to reduce the number of forward references.)
61
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62Additional documentation for Perl modules is available in the
63F</usr/local/man/> directory. Some of this is distributed standard with
64Perl, but you'll also find third-party modules there. You should be able
65to view this with your man(1) program by including the proper directories
66in the appropriate start-up files. To find out where these are, type:
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760ac839 68 perl -V:man.dir
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70If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
71you would only need to add F</usr/local/man> to your MANPATH. If
72they are different, you'll have to add both stems.
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73
74If that doesn't work for some reason, you can still use the
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75supplied F<perldoc> script to view module information. You might
76also look into getting a replacement man program.
16d20bd9 77
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78If something strange has gone wrong with your program and you're not
79sure where you should look for help, try the B<-w> switch first. It
80will often point out exactly where the trouble is.
81
82=head1 DESCRIPTION
83
84Perl is an interpreted language optimized for scanning arbitrary
85text files, extracting information from those text files, and printing
86reports based on that information. It's also a good language for many
87system management tasks. The language is intended to be practical
88(easy to use, efficient, complete) rather than beautiful (tiny,
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89elegant, minimal).
90
91Perl combines (in the author's opinion, anyway) some
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92of the best features of C, B<sed>, B<awk>, and B<sh>, so people
93familiar with those languages should have little difficulty with it.
94(Language historians will also note some vestiges of B<csh>, Pascal,
95and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
96expression syntax. Unlike most Unix utilities, Perl does not
97arbitrarily limit the size of your data--if you've got the memory,
98Perl can slurp in your whole file as a single string. Recursion is
99of unlimited depth. And the hash tables used by associative arrays
100grow as necessary to prevent degraded performance. Perl uses
101sophisticated pattern matching techniques to scan large amounts of data
102very quickly. Although optimized for scanning text, Perl can also
103deal with binary data, and can make dbm files look like associative
c07a80fd 104arrays. Setuid Perl scripts are safer than
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105C programs through a dataflow tracing mechanism which prevents many
106stupid security holes. If you have a problem that would ordinarily use
107B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
108run a little faster, and you don't want to write the silly thing in C,
109then Perl may be for you. There are also translators to turn your
110B<sed> and B<awk> scripts into Perl scripts.
111
112But wait, there's more...
113
114Perl version 5 is nearly a complete rewrite, and provides
115the following additional benefits:
116
117=over 5
118
119=item * Many usability enhancements
120
121It is now possible to write much more readable Perl code (even within
122regular expressions). Formerly cryptic variable names can be replaced
123by mnemonic identifiers. Error messages are more informative, and the
124optional warnings will catch many of the mistakes a novice might make.
125This cannot be stressed enough. Whenever you get mysterious behavior,
126try the B<-w> switch!!! Whenever you don't get mysterious behavior,
127try using B<-w> anyway.
128
129=item * Simplified grammar
130
131The new yacc grammar is one half the size of the old one. Many of the
132arbitrary grammar rules have been regularized. The number of reserved
133words has been cut by 2/3. Despite this, nearly all old Perl scripts
134will continue to work unchanged.
135
136=item * Lexical scoping
137
138Perl variables may now be declared within a lexical scope, like "auto"
139variables in C. Not only is this more efficient, but it contributes
140to better privacy for "programming in the large".
141
142=item * Arbitrarily nested data structures
143
144Any scalar value, including any array element, may now contain a
145reference to any other variable or subroutine. You can easily create
146anonymous variables and subroutines. Perl manages your reference
147counts for you.
148
149=item * Modularity and reusability
150
151The Perl library is now defined in terms of modules which can be easily
152shared among various packages. A package may choose to import all or a
153portion of a module's published interface. Pragmas (that is, compiler
154directives) are defined and used by the same mechanism.
155
156=item * Object-oriented programming
157
158A package can function as a class. Dynamic multiple inheritance and
159virtual methods are supported in a straightforward manner and with very
160little new syntax. Filehandles may now be treated as objects.
161
c07a80fd 162=item * Embeddable and Extensible
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163
164Perl may now be embedded easily in your C or C++ application, and can
165either call or be called by your routines through a documented
166interface. The XS preprocessor is provided to make it easy to glue
167your C or C++ routines into Perl. Dynamic loading of modules is
168supported.
169
170=item * POSIX compliant
171
172A major new module is the POSIX module, which provides access to all
173available POSIX routines and definitions, via object classes where
174appropriate.
175
176=item * Package constructors and destructors
177
178The new BEGIN and END blocks provide means to capture control as
179a package is being compiled, and after the program exits. As a
180degenerate case they work just like awk's BEGIN and END when you
181use the B<-p> or B<-n> switches.
182
183=item * Multiple simultaneous DBM implementations
184
185A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
186files from the same script simultaneously. In fact, the old dbmopen
187interface has been generalized to allow any variable to be tied
188to an object class which defines its access methods.
189
190=item * Subroutine definitions may now be autoloaded
191
192In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
193semantics for undefined subroutine calls. It's not just for autoloading.
194
195=item * Regular expression enhancements
196
197You can now specify non-greedy quantifiers. You can now do grouping
198without creating a backreference. You can now write regular expressions
199with embedded whitespace and comments for readability. A consistent
200extensibility mechanism has been added that is upwardly compatible with
201all old regular expressions.
202
203=back
204
205Ok, that's I<definitely> enough hype.
206
207=head1 ENVIRONMENT
208
209=over 12
210
211=item HOME
212
213Used if chdir has no argument.
214
215=item LOGDIR
216
217Used if chdir has no argument and HOME is not set.
218
219=item PATH
220
221Used in executing subprocesses, and in finding the script if B<-S> is
222used.
223
224=item PERL5LIB
225
226A colon-separated list of directories in which to look for Perl library
227files before looking in the standard library and the current
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228directory. If PERL5LIB is not defined, PERLLIB is used. When running
229taint checks (because the script was running setuid or setgid, or the
230B<-T> switch was used), neither variable is used. The script should
231instead say
232
233 use lib "/my/directory";
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234
235=item PERL5DB
236
237The command used to get the debugger code. If unset, uses
238
239 BEGIN { require 'perl5db.pl' }
240
241=item PERLLIB
242
243A colon-separated list of directories in which to look for Perl library
244files before looking in the standard library and the current
245directory. If PERL5LIB is defined, PERLLIB is not used.
246
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247=back
248
249Apart from these, Perl uses no other environment variables, except
250to make them available to the script being executed, and to child
251processes. However, scripts running setuid would do well to execute
252the following lines before doing anything else, just to keep people
253honest:
254
255 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
256 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
257 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
258
259=head1 AUTHOR
260
94d58c47 261Larry Wall E<lt>F<lwall@sems.com>E<gt>, with the help of oodles of other folks.
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262
263=head1 FILES
264
265 "/tmp/perl-e$$" temporary file for -e commands
266 "@INC" locations of perl 5 libraries
267
268=head1 SEE ALSO
269
270 a2p awk to perl translator
4633a7c4 271
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272 s2p sed to perl translator
273
274=head1 DIAGNOSTICS
275
276The B<-w> switch produces some lovely diagnostics.
277
278See L<perldiag> for explanations of all Perl's diagnostics.
279
280Compilation errors will tell you the line number of the error, with an
281indication of the next token or token type that was to be examined.
282(In the case of a script passed to Perl via B<-e> switches, each
283B<-e> is counted as one line.)
284
285Setuid scripts have additional constraints that can produce error
286messages such as "Insecure dependency". See L<perlsec>.
287
288Did we mention that you should definitely consider using the B<-w>
289switch?
290
291=head1 BUGS
292
293The B<-w> switch is not mandatory.
294
295Perl is at the mercy of your machine's definitions of various
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296operations such as type casting, atof() and sprintf(). The latter
297can even trigger a coredump when passed ludicrous input values.
a0d0e21e 298
748a9306 299If your stdio requires a seek or eof between reads and writes on a
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300particular stream, so does Perl. (This doesn't apply to sysread()
301and syswrite().)
302
303While none of the built-in data types have any arbitrary size limits
304(apart from memory size), there are still a few arbitrary limits: a
d357d931 305given variable name may not be longer than 255 characters, and no
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306component of your PATH may be longer than 255 if you use B<-S>. A regular
307expression may not compile to more than 32767 bytes internally.
308
94d58c47 309See the perl bugs database at F< http://perl.com/perl/bugs/ >. You may
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310mail your bug reports (be sure to include full configuration information
311as output by the myconfig program in the perl source tree) to
312F<perlbug@perl.com>.
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313If you've succeeded in compiling perl, the perlbug script in the utils/
314subdirectory can be used to help mail in a bug report.
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316Perl actually stands for Pathologically Eclectic Rubbish Lister, but
317don't tell anyone I said that.
318
319=head1 NOTES
320
321The Perl motto is "There's more than one way to do it." Divining
322how many more is left as an exercise to the reader.
323
4633a7c4 324The three principal virtues of a programmer are Laziness,
a0d0e21e 325Impatience, and Hubris. See the Camel Book for why.
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