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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> [ B<-acdhnpPsSTuUvw> ]
8[ S<B<-0>[I<octal>]> ]
9[ S<B<-D>I<number/list>]> ]
10[ S<B<-F>I<string>> ]
11[ S<B<-i>[I<extension>]> ]
12[ S<B<-I>I<dir>> ]
13[ S<B<-l>I<octal>> ]
14[ S<B<-x>I<dir>> ]
15[ I<programfile> | S<B<-e> I<command>> ]
16[ I<argument> ... ]
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,
83elegant, minimal). It combines (in the author's opinion, anyway) some
84of the best features of C, B<sed>, B<awk>, and B<sh>, so people
85familiar with those languages should have little difficulty with it.
86(Language historians will also note some vestiges of B<csh>, Pascal,
87and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
88expression syntax. Unlike most Unix utilities, Perl does not
89arbitrarily limit the size of your data--if you've got the memory,
90Perl can slurp in your whole file as a single string. Recursion is
91of unlimited depth. And the hash tables used by associative arrays
92grow as necessary to prevent degraded performance. Perl uses
93sophisticated pattern matching techniques to scan large amounts of data
94very quickly. Although optimized for scanning text, Perl can also
95deal with binary data, and can make dbm files look like associative
c07a80fd 96arrays. Setuid Perl scripts are safer than
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97C programs through a dataflow tracing mechanism which prevents many
98stupid security holes. If you have a problem that would ordinarily use
99B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
100run a little faster, and you don't want to write the silly thing in C,
101then Perl may be for you. There are also translators to turn your
102B<sed> and B<awk> scripts into Perl scripts.
103
104But wait, there's more...
105
106Perl version 5 is nearly a complete rewrite, and provides
107the following additional benefits:
108
109=over 5
110
111=item * Many usability enhancements
112
113It is now possible to write much more readable Perl code (even within
114regular expressions). Formerly cryptic variable names can be replaced
115by mnemonic identifiers. Error messages are more informative, and the
116optional warnings will catch many of the mistakes a novice might make.
117This cannot be stressed enough. Whenever you get mysterious behavior,
118try the B<-w> switch!!! Whenever you don't get mysterious behavior,
119try using B<-w> anyway.
120
121=item * Simplified grammar
122
123The new yacc grammar is one half the size of the old one. Many of the
124arbitrary grammar rules have been regularized. The number of reserved
125words has been cut by 2/3. Despite this, nearly all old Perl scripts
126will continue to work unchanged.
127
128=item * Lexical scoping
129
130Perl variables may now be declared within a lexical scope, like "auto"
131variables in C. Not only is this more efficient, but it contributes
132to better privacy for "programming in the large".
133
134=item * Arbitrarily nested data structures
135
136Any scalar value, including any array element, may now contain a
137reference to any other variable or subroutine. You can easily create
138anonymous variables and subroutines. Perl manages your reference
139counts for you.
140
141=item * Modularity and reusability
142
143The Perl library is now defined in terms of modules which can be easily
144shared among various packages. A package may choose to import all or a
145portion of a module's published interface. Pragmas (that is, compiler
146directives) are defined and used by the same mechanism.
147
148=item * Object-oriented programming
149
150A package can function as a class. Dynamic multiple inheritance and
151virtual methods are supported in a straightforward manner and with very
152little new syntax. Filehandles may now be treated as objects.
153
c07a80fd 154=item * Embeddable and Extensible
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155
156Perl may now be embedded easily in your C or C++ application, and can
157either call or be called by your routines through a documented
158interface. The XS preprocessor is provided to make it easy to glue
159your C or C++ routines into Perl. Dynamic loading of modules is
160supported.
161
162=item * POSIX compliant
163
164A major new module is the POSIX module, which provides access to all
165available POSIX routines and definitions, via object classes where
166appropriate.
167
168=item * Package constructors and destructors
169
170The new BEGIN and END blocks provide means to capture control as
171a package is being compiled, and after the program exits. As a
172degenerate case they work just like awk's BEGIN and END when you
173use the B<-p> or B<-n> switches.
174
175=item * Multiple simultaneous DBM implementations
176
177A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
178files from the same script simultaneously. In fact, the old dbmopen
179interface has been generalized to allow any variable to be tied
180to an object class which defines its access methods.
181
182=item * Subroutine definitions may now be autoloaded
183
184In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
185semantics for undefined subroutine calls. It's not just for autoloading.
186
187=item * Regular expression enhancements
188
189You can now specify non-greedy quantifiers. You can now do grouping
190without creating a backreference. You can now write regular expressions
191with embedded whitespace and comments for readability. A consistent
192extensibility mechanism has been added that is upwardly compatible with
193all old regular expressions.
194
195=back
196
197Ok, that's I<definitely> enough hype.
198
199=head1 ENVIRONMENT
200
201=over 12
202
203=item HOME
204
205Used if chdir has no argument.
206
207=item LOGDIR
208
209Used if chdir has no argument and HOME is not set.
210
211=item PATH
212
213Used in executing subprocesses, and in finding the script if B<-S> is
214used.
215
216=item PERL5LIB
217
218A colon-separated list of directories in which to look for Perl library
219files before looking in the standard library and the current
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220directory. If PERL5LIB is not defined, PERLLIB is used. When running
221taint checks (because the script was running setuid or setgid, or the
222B<-T> switch was used), neither variable is used. The script should
223instead say
224
225 use lib "/my/directory";
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226
227=item PERL5DB
228
229The command used to get the debugger code. If unset, uses
230
231 BEGIN { require 'perl5db.pl' }
232
233=item PERLLIB
234
235A colon-separated list of directories in which to look for Perl library
236files before looking in the standard library and the current
237directory. If PERL5LIB is defined, PERLLIB is not used.
238
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239=back
240
241Apart from these, Perl uses no other environment variables, except
242to make them available to the script being executed, and to child
243processes. However, scripts running setuid would do well to execute
244the following lines before doing anything else, just to keep people
245honest:
246
247 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
248 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
249 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
250
251=head1 AUTHOR
252
c07a80fd 253Larry Wall E<lt><F<lwall@sems.com>E<gt>, with the help of oodles of other folks.
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254
255=head1 FILES
256
257 "/tmp/perl-e$$" temporary file for -e commands
258 "@INC" locations of perl 5 libraries
259
260=head1 SEE ALSO
261
262 a2p awk to perl translator
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264 s2p sed to perl translator
265
266=head1 DIAGNOSTICS
267
268The B<-w> switch produces some lovely diagnostics.
269
270See L<perldiag> for explanations of all Perl's diagnostics.
271
272Compilation errors will tell you the line number of the error, with an
273indication of the next token or token type that was to be examined.
274(In the case of a script passed to Perl via B<-e> switches, each
275B<-e> is counted as one line.)
276
277Setuid scripts have additional constraints that can produce error
278messages such as "Insecure dependency". See L<perlsec>.
279
280Did we mention that you should definitely consider using the B<-w>
281switch?
282
283=head1 BUGS
284
285The B<-w> switch is not mandatory.
286
287Perl is at the mercy of your machine's definitions of various
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288operations such as type casting, atof() and sprintf(). The latter
289can even trigger a coredump when passed ludicrous input values.
a0d0e21e 290
748a9306 291If your stdio requires a seek or eof between reads and writes on a
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292particular stream, so does Perl. (This doesn't apply to sysread()
293and syswrite().)
294
295While none of the built-in data types have any arbitrary size limits
296(apart from memory size), there are still a few arbitrary limits: a
297given identifier may not be longer than 255 characters, and no
298component of your PATH may be longer than 255 if you use B<-S>. A regular
299expression may not compile to more than 32767 bytes internally.
300
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301See the perl bugs database at F<http://perl.com/perl/bugs/>. You may
302mail your bug reports (be sure to include full configuration information
303as output by the myconfig program in the perl source tree) to
304F<perlbug@perl.com>.
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305If you've succeeded in compiling perl, the perlbug script in the utils/
306subdirectory can be used to help mail in a bug report.
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308Perl actually stands for Pathologically Eclectic Rubbish Lister, but
309don't tell anyone I said that.
310
311=head1 NOTES
312
313The Perl motto is "There's more than one way to do it." Divining
314how many more is left as an exercise to the reader.
315
4633a7c4 316The three principal virtues of a programmer are Laziness,
a0d0e21e 317Impatience, and Hubris. See the Camel Book for why.
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