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1=head1 NAME
2
3perl - Practical Extraction and Report Language
4
5=head1 SYNOPSIS
6
7For ease of access, the Perl manual has been split up into a number
8of sections:
9
10 perl Perl overview (this section)
cb1a09d0 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
a0d0e21e 24 perlobj Perl objects
cb1a09d0 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
8e07c86e 34 perlxs Perl XS application programming interface
4633a7c4 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,
43the suggested order will tend to reduce the number of forward references.)
44
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45Additional documentation for Perl modules is available in the
46F</usr/local/man/> directory. Some of this is distributed standard with
47Perl, but you'll also find third-party modules there. You should be able
48to view this with your man(1) program by including the proper directories
49in the appropriate start-up files. To find out where these are, type:
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4633a7c4 51 perl -le 'use Config; print "@Config{man1dir,man3dir}"'
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53If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
54you would only need to add F</usr/local/man> to your MANPATH. If
55they are different, you'll have to add both stems.
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56
57If that doesn't work for some reason, you can still use the
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58supplied F<perldoc> script to view module information. You might
59also look into getting a replacement man program.
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61If something strange has gone wrong with your program and you're not
62sure where you should look for help, try the B<-w> switch first. It
63will often point out exactly where the trouble is.
64
65=head1 DESCRIPTION
66
67Perl is an interpreted language optimized for scanning arbitrary
68text files, extracting information from those text files, and printing
69reports based on that information. It's also a good language for many
70system management tasks. The language is intended to be practical
71(easy to use, efficient, complete) rather than beautiful (tiny,
72elegant, minimal). It combines (in the author's opinion, anyway) some
73of the best features of C, B<sed>, B<awk>, and B<sh>, so people
74familiar with those languages should have little difficulty with it.
75(Language historians will also note some vestiges of B<csh>, Pascal,
76and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
77expression syntax. Unlike most Unix utilities, Perl does not
78arbitrarily limit the size of your data--if you've got the memory,
79Perl can slurp in your whole file as a single string. Recursion is
80of unlimited depth. And the hash tables used by associative arrays
81grow as necessary to prevent degraded performance. Perl uses
82sophisticated pattern matching techniques to scan large amounts of data
83very quickly. Although optimized for scanning text, Perl can also
84deal with binary data, and can make dbm files look like associative
85arrays (where dbm is available). Setuid Perl scripts are safer than
86C programs through a dataflow tracing mechanism which prevents many
87stupid security holes. If you have a problem that would ordinarily use
88B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
89run a little faster, and you don't want to write the silly thing in C,
90then Perl may be for you. There are also translators to turn your
91B<sed> and B<awk> scripts into Perl scripts.
92
93But wait, there's more...
94
95Perl version 5 is nearly a complete rewrite, and provides
96the following additional benefits:
97
98=over 5
99
100=item * Many usability enhancements
101
102It is now possible to write much more readable Perl code (even within
103regular expressions). Formerly cryptic variable names can be replaced
104by mnemonic identifiers. Error messages are more informative, and the
105optional warnings will catch many of the mistakes a novice might make.
106This cannot be stressed enough. Whenever you get mysterious behavior,
107try the B<-w> switch!!! Whenever you don't get mysterious behavior,
108try using B<-w> anyway.
109
110=item * Simplified grammar
111
112The new yacc grammar is one half the size of the old one. Many of the
113arbitrary grammar rules have been regularized. The number of reserved
114words has been cut by 2/3. Despite this, nearly all old Perl scripts
115will continue to work unchanged.
116
117=item * Lexical scoping
118
119Perl variables may now be declared within a lexical scope, like "auto"
120variables in C. Not only is this more efficient, but it contributes
121to better privacy for "programming in the large".
122
123=item * Arbitrarily nested data structures
124
125Any scalar value, including any array element, may now contain a
126reference to any other variable or subroutine. You can easily create
127anonymous variables and subroutines. Perl manages your reference
128counts for you.
129
130=item * Modularity and reusability
131
132The Perl library is now defined in terms of modules which can be easily
133shared among various packages. A package may choose to import all or a
134portion of a module's published interface. Pragmas (that is, compiler
135directives) are defined and used by the same mechanism.
136
137=item * Object-oriented programming
138
139A package can function as a class. Dynamic multiple inheritance and
140virtual methods are supported in a straightforward manner and with very
141little new syntax. Filehandles may now be treated as objects.
142
143=item * Embeddible and Extensible
144
145Perl may now be embedded easily in your C or C++ application, and can
146either call or be called by your routines through a documented
147interface. The XS preprocessor is provided to make it easy to glue
148your C or C++ routines into Perl. Dynamic loading of modules is
149supported.
150
151=item * POSIX compliant
152
153A major new module is the POSIX module, which provides access to all
154available POSIX routines and definitions, via object classes where
155appropriate.
156
157=item * Package constructors and destructors
158
159The new BEGIN and END blocks provide means to capture control as
160a package is being compiled, and after the program exits. As a
161degenerate case they work just like awk's BEGIN and END when you
162use the B<-p> or B<-n> switches.
163
164=item * Multiple simultaneous DBM implementations
165
166A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
167files from the same script simultaneously. In fact, the old dbmopen
168interface has been generalized to allow any variable to be tied
169to an object class which defines its access methods.
170
171=item * Subroutine definitions may now be autoloaded
172
173In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
174semantics for undefined subroutine calls. It's not just for autoloading.
175
176=item * Regular expression enhancements
177
178You can now specify non-greedy quantifiers. You can now do grouping
179without creating a backreference. You can now write regular expressions
180with embedded whitespace and comments for readability. A consistent
181extensibility mechanism has been added that is upwardly compatible with
182all old regular expressions.
183
184=back
185
186Ok, that's I<definitely> enough hype.
187
188=head1 ENVIRONMENT
189
190=over 12
191
192=item HOME
193
194Used if chdir has no argument.
195
196=item LOGDIR
197
198Used if chdir has no argument and HOME is not set.
199
200=item PATH
201
202Used in executing subprocesses, and in finding the script if B<-S> is
203used.
204
205=item PERL5LIB
206
207A colon-separated list of directories in which to look for Perl library
208files before looking in the standard library and the current
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209directory. If PERL5LIB is not defined, PERLLIB is used. When running
210taint checks (because the script was running setuid or setgid, or the
211B<-T> switch was used), neither variable is used. The script should
212instead say
213
214 use lib "/my/directory";
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215
216=item PERL5DB
217
218The command used to get the debugger code. If unset, uses
219
220 BEGIN { require 'perl5db.pl' }
221
222=item PERLLIB
223
224A colon-separated list of directories in which to look for Perl library
225files before looking in the standard library and the current
226directory. If PERL5LIB is defined, PERLLIB is not used.
227
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228=back
229
230Apart from these, Perl uses no other environment variables, except
231to make them available to the script being executed, and to child
232processes. However, scripts running setuid would do well to execute
233the following lines before doing anything else, just to keep people
234honest:
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
4633a7c4 242Larry 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
4633a7c4 252
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253 s2p sed to perl translator
254
255=head1 DIAGNOSTICS
256
257The B<-w> switch produces some lovely diagnostics.
258
259See L<perldiag> for explanations of all Perl's diagnostics.
260
261Compilation errors will tell you the line number of the error, with an
262indication 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
264B<-e> is counted as one line.)
265
266Setuid scripts have additional constraints that can produce error
267messages such as "Insecure dependency". See L<perlsec>.
268
269Did we mention that you should definitely consider using the B<-w>
270switch?
271
272=head1 BUGS
273
274The B<-w> switch is not mandatory.
275
276Perl is at the mercy of your machine's definitions of various
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277operations such as type casting, atof() and sprintf(). The latter
278can even trigger a coredump when passed ludicrous input values.
a0d0e21e 279
748a9306 280If your stdio requires a seek or eof between reads and writes on a
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281particular stream, so does Perl. (This doesn't apply to sysread()
282and syswrite().)
283
284While 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
286given identifier may not be longer than 255 characters, and no
287component of your PATH may be longer than 255 if you use B<-S>. A regular
288expression may not compile to more than 32767 bytes internally.
289
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290See the perl bugs database at F<http://perl.com/perl/bugs/>. You may
291mail your bug reports (be sure to include full configuration information
292as output by the myconfig program in the perl source tree) to
293F<perlbug@perl.com>.
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295Perl actually stands for Pathologically Eclectic Rubbish Lister, but
296don't tell anyone I said that.
297
298=head1 NOTES
299
300The Perl motto is "There's more than one way to do it." Divining
301how many more is left as an exercise to the reader.
302
4633a7c4 303The three principal virtues of a programmer are Laziness,
a0d0e21e 304Impatience, and Hubris. See the Camel Book for why.
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