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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)
774d564b 22 perldelta Perl changes since previous version
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
5f05dabc 34 perllocale Perl locale support
760ac839 35
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36 perlref Perl references
37 perldsc Perl data structures intro
38 perllol Perl data structures: lists of lists
5f05dabc 39 perltoot Perl OO tutorial
a0d0e21e 40 perlobj Perl objects
cb1a09d0 41 perltie Perl objects hidden behind simple variables
a0d0e21e 42 perlbot Perl OO tricks and examples
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43 perlipc Perl interprocess communication
44
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45 perldebug Perl debugging
46 perldiag Perl diagnostic messages
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47 perlsec Perl security
48 perltrap Perl traps for the unwary
49 perlstyle Perl style guide
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50
51 perlpod Perl plain old documentation
52 perlbook Perl book information
53
54 perlembed Perl how to embed perl in your C or C++ app
55 perlapio Perl internal IO abstraction interface
8e07c86e 56 perlxs Perl XS application programming interface
4633a7c4 57 perlxstut Perl XS tutorial
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58 perlguts Perl internal functions for those doing extensions
59 perlcall Perl calling conventions from C
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60
61(If you're intending to read these straight through for the first time,
62the suggested order will tend to reduce the number of forward references.)
63
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64Additional documentation for Perl modules is available in the
65F</usr/local/man/> directory. Some of this is distributed standard with
66Perl, but you'll also find third-party modules there. You should be able
67to view this with your man(1) program by including the proper directories
68in the appropriate start-up files. To find out where these are, type:
16d20bd9 69
760ac839 70 perl -V:man.dir
16d20bd9 71
4633a7c4 72If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
5f05dabc 73you would need to add only F</usr/local/man> to your MANPATH. If
4633a7c4 74they are different, you'll have to add both stems.
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75
76If that doesn't work for some reason, you can still use the
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77supplied F<perldoc> script to view module information. You might
78also look into getting a replacement man program.
16d20bd9 79
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80If something strange has gone wrong with your program and you're not
81sure where you should look for help, try the B<-w> switch first. It
82will often point out exactly where the trouble is.
83
84=head1 DESCRIPTION
85
5f05dabc 86Perl is a language optimized for scanning arbitrary
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87text files, extracting information from those text files, and printing
88reports based on that information. It's also a good language for many
89system management tasks. The language is intended to be practical
90(easy to use, efficient, complete) rather than beautiful (tiny,
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91elegant, minimal).
92
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93Perl combines (in the author's opinion, anyway) some of the best
94features of C, B<sed>, B<awk>, and B<sh>, so people familiar with
95those languages should have little difficulty with it. (Language
96historians will also note some vestiges of B<csh>, Pascal, and even
97BASIC-PLUS.) Expression syntax corresponds quite closely to C
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98expression syntax. Unlike most Unix utilities, Perl does not
99arbitrarily limit the size of your data--if you've got the memory,
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100Perl can slurp in your whole file as a single string. Recursion is of
101unlimited depth. And the tables used by hashes (previously called
102"associative arrays") grow as necessary to prevent degraded
103performance. Perl uses sophisticated pattern matching techniques to
104scan large amounts of data very quickly. Although optimized for
105scanning text, Perl can also deal with binary data, and can make dbm
106files look like hashes. Setuid Perl scripts are safer than C programs
107through a dataflow tracing mechanism which prevents many stupid
108security holes.
109
110If you have a problem that would ordinarily use B<sed> or B<awk> or
111B<sh>, but it exceeds their capabilities or must run a little faster,
112and you don't want to write the silly thing in C, then Perl may be for
113you. There are also translators to turn your B<sed> and B<awk>
114scripts into Perl scripts.
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115
116But wait, there's more...
117
118Perl version 5 is nearly a complete rewrite, and provides
119the following additional benefits:
120
121=over 5
122
123=item * Many usability enhancements
124
125It is now possible to write much more readable Perl code (even within
126regular expressions). Formerly cryptic variable names can be replaced
127by mnemonic identifiers. Error messages are more informative, and the
128optional warnings will catch many of the mistakes a novice might make.
129This cannot be stressed enough. Whenever you get mysterious behavior,
130try the B<-w> switch!!! Whenever you don't get mysterious behavior,
131try using B<-w> anyway.
132
133=item * Simplified grammar
134
135The new yacc grammar is one half the size of the old one. Many of the
136arbitrary grammar rules have been regularized. The number of reserved
137words has been cut by 2/3. Despite this, nearly all old Perl scripts
138will continue to work unchanged.
139
140=item * Lexical scoping
141
142Perl variables may now be declared within a lexical scope, like "auto"
143variables in C. Not only is this more efficient, but it contributes
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144to better privacy for "programming in the large". Anonymous
145subroutines exhibit deep binding of lexical variables (closures).
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146
147=item * Arbitrarily nested data structures
148
149Any scalar value, including any array element, may now contain a
150reference to any other variable or subroutine. You can easily create
151anonymous variables and subroutines. Perl manages your reference
152counts for you.
153
154=item * Modularity and reusability
155
156The Perl library is now defined in terms of modules which can be easily
157shared among various packages. A package may choose to import all or a
158portion of a module's published interface. Pragmas (that is, compiler
159directives) are defined and used by the same mechanism.
160
161=item * Object-oriented programming
162
163A package can function as a class. Dynamic multiple inheritance and
164virtual methods are supported in a straightforward manner and with very
165little new syntax. Filehandles may now be treated as objects.
166
c07a80fd 167=item * Embeddable and Extensible
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168
169Perl may now be embedded easily in your C or C++ application, and can
170either call or be called by your routines through a documented
171interface. The XS preprocessor is provided to make it easy to glue
172your C or C++ routines into Perl. Dynamic loading of modules is
5f05dabc 173supported, and Perl itself can be made into a dynamic library.
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174
175=item * POSIX compliant
176
177A major new module is the POSIX module, which provides access to all
178available POSIX routines and definitions, via object classes where
179appropriate.
180
181=item * Package constructors and destructors
182
183The new BEGIN and END blocks provide means to capture control as
184a package is being compiled, and after the program exits. As a
185degenerate case they work just like awk's BEGIN and END when you
186use the B<-p> or B<-n> switches.
187
188=item * Multiple simultaneous DBM implementations
189
190A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
191files from the same script simultaneously. In fact, the old dbmopen
192interface has been generalized to allow any variable to be tied
193to an object class which defines its access methods.
194
195=item * Subroutine definitions may now be autoloaded
196
197In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
5f05dabc 198semantics for undefined subroutine calls. It's not for just autoloading.
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199
200=item * Regular expression enhancements
201
202You can now specify non-greedy quantifiers. You can now do grouping
203without creating a backreference. You can now write regular expressions
204with embedded whitespace and comments for readability. A consistent
205extensibility mechanism has been added that is upwardly compatible with
206all old regular expressions.
207
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208=item * Innumerable Unbundled Modules
209
210The Comprehensive Perl Archive Network described in L<perlmod>
211contains hundreds of plug-and-play modules full of reusable
212code. See F<http://www.perl.com/CPAN> for a site near you.
213
214=item * Compilability
215
216While not yet in full production mode, a working perl-to-C compiler
217does exist. It can generate portable bytecode, simple C, or
218optimized C code.
219
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220=back
221
222Ok, that's I<definitely> enough hype.
223
224=head1 ENVIRONMENT
225
1e422769 226See L<perlrun>.
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227
228=head1 AUTHOR
229
9607fc9c 230Larry Wall <F<larry@wall.org>>, with the help of oodles of other folks.
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231
232=head1 FILES
233
234 "/tmp/perl-e$$" temporary file for -e commands
5f05dabc 235 "@INC" locations of perl libraries
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236
237=head1 SEE ALSO
238
239 a2p awk to perl translator
4633a7c4 240
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241 s2p sed to perl translator
242
243=head1 DIAGNOSTICS
244
245The B<-w> switch produces some lovely diagnostics.
246
247See L<perldiag> for explanations of all Perl's diagnostics.
248
249Compilation errors will tell you the line number of the error, with an
250indication of the next token or token type that was to be examined.
251(In the case of a script passed to Perl via B<-e> switches, each
252B<-e> is counted as one line.)
253
254Setuid scripts have additional constraints that can produce error
255messages such as "Insecure dependency". See L<perlsec>.
256
257Did we mention that you should definitely consider using the B<-w>
258switch?
259
260=head1 BUGS
261
262The B<-w> switch is not mandatory.
263
264Perl is at the mercy of your machine's definitions of various
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265operations such as type casting, atof(), and sprintf(). The latter
266can even trigger a core dump when passed ludicrous input values.
a0d0e21e 267
748a9306 268If your stdio requires a seek or eof between reads and writes on a
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269particular stream, so does Perl. (This doesn't apply to sysread()
270and syswrite().)
271
272While none of the built-in data types have any arbitrary size limits
273(apart from memory size), there are still a few arbitrary limits: a
d357d931 274given variable name may not be longer than 255 characters, and no
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275component of your PATH may be longer than 255 if you use B<-S>. A regular
276expression may not compile to more than 32767 bytes internally.
277
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278You may mail your bug reports (be sure to include full configuration
279information as output by the myconfig program in the perl source tree,
9607fc9c 280or by C<perl -V>) to <F<perlbug@perl.com>>.
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281If you've succeeded in compiling perl, the perlbug script in the utils/
282subdirectory can be used to help mail in a bug report.
4633a7c4 283
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284Perl actually stands for Pathologically Eclectic Rubbish Lister, but
285don't tell anyone I said that.
286
287=head1 NOTES
288
289The Perl motto is "There's more than one way to do it." Divining
290how many more is left as an exercise to the reader.
291
4633a7c4 292The three principal virtues of a programmer are Laziness,
a0d0e21e 293Impatience, and Hubris. See the Camel Book for why.
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