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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
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23 perldata Perl data structures
24 perlsyn Perl syntax
25 perlop Perl operators and precedence
26 perlre Perl regular expressions
27 perlrun Perl execution and options
28 perlfunc Perl builtin functions
29 perlvar Perl predefined variables
30 perlsub Perl subroutines
31 perlmod Perl modules
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32 perlref Perl references
33 perldsc Perl data structures intro
34 perllol Perl data structures: lists of lists
a0d0e21e 35 perlobj Perl objects
cb1a09d0 36 perltie Perl objects hidden behind simple variables
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37 perlbot Perl OO tricks and examples
38 perldebug Perl debugging
39 perldiag Perl diagnostic messages
40 perlform Perl formats
41 perlipc Perl interprocess communication
42 perlsec Perl security
43 perltrap Perl traps for the unwary
44 perlstyle Perl style guide
8e07c86e 45 perlxs Perl XS application programming interface
4633a7c4 46 perlxstut Perl XS tutorial
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47 perlguts Perl internal functions for those doing extensions
48 perlcall Perl calling conventions from C
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49 perlembed Perl how to embed perl in your C or C++ app
50 perlpod Perl plain old documentation
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51 perlbook Perl book information
52
53(If you're intending to read these straight through for the first time,
54the suggested order will tend to reduce the number of forward references.)
55
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56Additional documentation for Perl modules is available in the
57F</usr/local/man/> directory. Some of this is distributed standard with
58Perl, but you'll also find third-party modules there. You should be able
59to view this with your man(1) program by including the proper directories
60in the appropriate start-up files. To find out where these are, type:
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4633a7c4 62 perl -le 'use Config; print "@Config{man1dir,man3dir}"'
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64If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
65you would only need to add F</usr/local/man> to your MANPATH. If
66they are different, you'll have to add both stems.
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67
68If that doesn't work for some reason, you can still use the
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69supplied F<perldoc> script to view module information. You might
70also look into getting a replacement man program.
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72If something strange has gone wrong with your program and you're not
73sure where you should look for help, try the B<-w> switch first. It
74will often point out exactly where the trouble is.
75
76=head1 DESCRIPTION
77
78Perl is an interpreted language optimized for scanning arbitrary
79text files, extracting information from those text files, and printing
80reports based on that information. It's also a good language for many
81system management tasks. The language is intended to be practical
82(easy to use, efficient, complete) rather than beautiful (tiny,
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83elegant, minimal).
84
85Perl combines (in the author's opinion, anyway) some
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86of the best features of C, B<sed>, B<awk>, and B<sh>, so people
87familiar with those languages should have little difficulty with it.
88(Language historians will also note some vestiges of B<csh>, Pascal,
89and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
90expression syntax. Unlike most Unix utilities, Perl does not
91arbitrarily limit the size of your data--if you've got the memory,
92Perl can slurp in your whole file as a single string. Recursion is
93of unlimited depth. And the hash tables used by associative arrays
94grow as necessary to prevent degraded performance. Perl uses
95sophisticated pattern matching techniques to scan large amounts of data
96very quickly. Although optimized for scanning text, Perl can also
97deal with binary data, and can make dbm files look like associative
c07a80fd 98arrays. Setuid Perl scripts are safer than
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99C programs through a dataflow tracing mechanism which prevents many
100stupid security holes. If you have a problem that would ordinarily use
101B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
102run a little faster, and you don't want to write the silly thing in C,
103then Perl may be for you. There are also translators to turn your
104B<sed> and B<awk> scripts into Perl scripts.
105
106But wait, there's more...
107
108Perl version 5 is nearly a complete rewrite, and provides
109the following additional benefits:
110
111=over 5
112
113=item * Many usability enhancements
114
115It is now possible to write much more readable Perl code (even within
116regular expressions). Formerly cryptic variable names can be replaced
117by mnemonic identifiers. Error messages are more informative, and the
118optional warnings will catch many of the mistakes a novice might make.
119This cannot be stressed enough. Whenever you get mysterious behavior,
120try the B<-w> switch!!! Whenever you don't get mysterious behavior,
121try using B<-w> anyway.
122
123=item * Simplified grammar
124
125The new yacc grammar is one half the size of the old one. Many of the
126arbitrary grammar rules have been regularized. The number of reserved
127words has been cut by 2/3. Despite this, nearly all old Perl scripts
128will continue to work unchanged.
129
130=item * Lexical scoping
131
132Perl variables may now be declared within a lexical scope, like "auto"
133variables in C. Not only is this more efficient, but it contributes
134to better privacy for "programming in the large".
135
136=item * Arbitrarily nested data structures
137
138Any scalar value, including any array element, may now contain a
139reference to any other variable or subroutine. You can easily create
140anonymous variables and subroutines. Perl manages your reference
141counts for you.
142
143=item * Modularity and reusability
144
145The Perl library is now defined in terms of modules which can be easily
146shared among various packages. A package may choose to import all or a
147portion of a module's published interface. Pragmas (that is, compiler
148directives) are defined and used by the same mechanism.
149
150=item * Object-oriented programming
151
152A package can function as a class. Dynamic multiple inheritance and
153virtual methods are supported in a straightforward manner and with very
154little new syntax. Filehandles may now be treated as objects.
155
c07a80fd 156=item * Embeddable and Extensible
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157
158Perl may now be embedded easily in your C or C++ application, and can
159either call or be called by your routines through a documented
160interface. The XS preprocessor is provided to make it easy to glue
161your C or C++ routines into Perl. Dynamic loading of modules is
162supported.
163
164=item * POSIX compliant
165
166A major new module is the POSIX module, which provides access to all
167available POSIX routines and definitions, via object classes where
168appropriate.
169
170=item * Package constructors and destructors
171
172The new BEGIN and END blocks provide means to capture control as
173a package is being compiled, and after the program exits. As a
174degenerate case they work just like awk's BEGIN and END when you
175use the B<-p> or B<-n> switches.
176
177=item * Multiple simultaneous DBM implementations
178
179A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
180files from the same script simultaneously. In fact, the old dbmopen
181interface has been generalized to allow any variable to be tied
182to an object class which defines its access methods.
183
184=item * Subroutine definitions may now be autoloaded
185
186In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
187semantics for undefined subroutine calls. It's not just for autoloading.
188
189=item * Regular expression enhancements
190
191You can now specify non-greedy quantifiers. You can now do grouping
192without creating a backreference. You can now write regular expressions
193with embedded whitespace and comments for readability. A consistent
194extensibility mechanism has been added that is upwardly compatible with
195all old regular expressions.
196
197=back
198
199Ok, that's I<definitely> enough hype.
200
201=head1 ENVIRONMENT
202
203=over 12
204
205=item HOME
206
207Used if chdir has no argument.
208
209=item LOGDIR
210
211Used if chdir has no argument and HOME is not set.
212
213=item PATH
214
215Used in executing subprocesses, and in finding the script if B<-S> is
216used.
217
218=item PERL5LIB
219
220A colon-separated list of directories in which to look for Perl library
221files before looking in the standard library and the current
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222directory. If PERL5LIB is not defined, PERLLIB is used. When running
223taint checks (because the script was running setuid or setgid, or the
224B<-T> switch was used), neither variable is used. The script should
225instead say
226
227 use lib "/my/directory";
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228
229=item PERL5DB
230
231The command used to get the debugger code. If unset, uses
232
233 BEGIN { require 'perl5db.pl' }
234
235=item PERLLIB
236
237A colon-separated list of directories in which to look for Perl library
238files before looking in the standard library and the current
239directory. If PERL5LIB is defined, PERLLIB is not used.
240
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241=back
242
243Apart from these, Perl uses no other environment variables, except
244to make them available to the script being executed, and to child
245processes. However, scripts running setuid would do well to execute
246the following lines before doing anything else, just to keep people
247honest:
248
249 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
250 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
251 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
252
253=head1 AUTHOR
254
94d58c47 255Larry Wall E<lt>F<lwall@sems.com>E<gt>, with the help of oodles of other folks.
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256
257=head1 FILES
258
259 "/tmp/perl-e$$" temporary file for -e commands
260 "@INC" locations of perl 5 libraries
261
262=head1 SEE ALSO
263
264 a2p awk to perl translator
4633a7c4 265
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266 s2p sed to perl translator
267
268=head1 DIAGNOSTICS
269
270The B<-w> switch produces some lovely diagnostics.
271
272See L<perldiag> for explanations of all Perl's diagnostics.
273
274Compilation errors will tell you the line number of the error, with an
275indication of the next token or token type that was to be examined.
276(In the case of a script passed to Perl via B<-e> switches, each
277B<-e> is counted as one line.)
278
279Setuid scripts have additional constraints that can produce error
280messages such as "Insecure dependency". See L<perlsec>.
281
282Did we mention that you should definitely consider using the B<-w>
283switch?
284
285=head1 BUGS
286
287The B<-w> switch is not mandatory.
288
289Perl is at the mercy of your machine's definitions of various
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290operations such as type casting, atof() and sprintf(). The latter
291can even trigger a coredump when passed ludicrous input values.
a0d0e21e 292
748a9306 293If your stdio requires a seek or eof between reads and writes on a
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294particular stream, so does Perl. (This doesn't apply to sysread()
295and syswrite().)
296
297While none of the built-in data types have any arbitrary size limits
298(apart from memory size), there are still a few arbitrary limits: a
d357d931 299given variable name may not be longer than 255 characters, and no
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300component of your PATH may be longer than 255 if you use B<-S>. A regular
301expression may not compile to more than 32767 bytes internally.
302
94d58c47 303See the perl bugs database at F< http://perl.com/perl/bugs/ >. You may
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304mail your bug reports (be sure to include full configuration information
305as output by the myconfig program in the perl source tree) to
306F<perlbug@perl.com>.
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307If you've succeeded in compiling perl, the perlbug script in the utils/
308subdirectory can be used to help mail in a bug report.
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310Perl actually stands for Pathologically Eclectic Rubbish Lister, but
311don't tell anyone I said that.
312
313=head1 NOTES
314
315The Perl motto is "There's more than one way to do it." Divining
316how many more is left as an exercise to the reader.
317
4633a7c4 318The three principal virtues of a programmer are Laziness,
a0d0e21e 319Impatience, and Hubris. See the Camel Book for why.
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