This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
[dummy merge]
[perl5.git] / pod / perl.pod
CommitLineData
a0d0e21e
LW
1=head1 NAME
2
3perl - Practical Extraction and Report Language
4
5=head1 SYNOPSIS
6
94d58c47
PP
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
a0d0e21e
LW
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
68dc0745 23 perlfaq Perl frequently asked questions
760ac839 24
a0d0e21e
LW
25 perldata Perl data structures
26 perlsyn Perl syntax
27 perlop Perl operators and precedence
28 perlre Perl regular expressions
29 perlrun Perl execution and options
30 perlfunc Perl builtin functions
31 perlvar Perl predefined variables
32 perlsub Perl subroutines
33 perlmod Perl modules
760ac839 34 perlform Perl formats
5f05dabc 35 perllocale Perl locale support
760ac839 36
4633a7c4
LW
37 perlref Perl references
38 perldsc Perl data structures intro
39 perllol Perl data structures: lists of lists
5f05dabc 40 perltoot Perl OO tutorial
a0d0e21e 41 perlobj Perl objects
cb1a09d0 42 perltie Perl objects hidden behind simple variables
a0d0e21e 43 perlbot Perl OO tricks and examples
760ac839
LW
44 perlipc Perl interprocess communication
45
a0d0e21e
LW
46 perldebug Perl debugging
47 perldiag Perl diagnostic messages
a0d0e21e
LW
48 perlsec Perl security
49 perltrap Perl traps for the unwary
50 perlstyle Perl style guide
760ac839
LW
51
52 perlpod Perl plain old documentation
53 perlbook Perl book information
54
55 perlembed Perl how to embed perl in your C or C++ app
56 perlapio Perl internal IO abstraction interface
8e07c86e 57 perlxs Perl XS application programming interface
4633a7c4 58 perlxstut Perl XS tutorial
a0d0e21e
LW
59 perlguts Perl internal functions for those doing extensions
60 perlcall Perl calling conventions from C
a0d0e21e
LW
61
62(If you're intending to read these straight through for the first time,
63the suggested order will tend to reduce the number of forward references.)
64
4633a7c4
LW
65Additional documentation for Perl modules is available in the
66F</usr/local/man/> directory. Some of this is distributed standard with
67Perl, but you'll also find third-party modules there. You should be able
68to view this with your man(1) program by including the proper directories
69in the appropriate start-up files. To find out where these are, type:
16d20bd9 70
760ac839 71 perl -V:man.dir
16d20bd9 72
4633a7c4 73If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
5f05dabc 74you would need to add only F</usr/local/man> to your MANPATH. If
4633a7c4 75they are different, you'll have to add both stems.
16d20bd9
AD
76
77If that doesn't work for some reason, you can still use the
4633a7c4
LW
78supplied F<perldoc> script to view module information. You might
79also look into getting a replacement man program.
16d20bd9 80
a0d0e21e
LW
81If something strange has gone wrong with your program and you're not
82sure where you should look for help, try the B<-w> switch first. It
83will often point out exactly where the trouble is.
84
85=head1 DESCRIPTION
86
5f05dabc 87Perl is a language optimized for scanning arbitrary
a0d0e21e
LW
88text files, extracting information from those text files, and printing
89reports based on that information. It's also a good language for many
90system management tasks. The language is intended to be practical
91(easy to use, efficient, complete) rather than beautiful (tiny,
94d58c47
PP
92elegant, minimal).
93
aa689395
PP
94Perl combines (in the author's opinion, anyway) some of the best
95features of C, B<sed>, B<awk>, and B<sh>, so people familiar with
96those languages should have little difficulty with it. (Language
97historians will also note some vestiges of B<csh>, Pascal, and even
98BASIC-PLUS.) Expression syntax corresponds quite closely to C
a0d0e21e
LW
99expression syntax. Unlike most Unix utilities, Perl does not
100arbitrarily limit the size of your data--if you've got the memory,
aa689395
PP
101Perl can slurp in your whole file as a single string. Recursion is of
102unlimited depth. And the tables used by hashes (previously called
103"associative arrays") grow as necessary to prevent degraded
104performance. Perl uses sophisticated pattern matching techniques to
105scan large amounts of data very quickly. Although optimized for
106scanning text, Perl can also deal with binary data, and can make dbm
107files look like hashes. Setuid Perl scripts are safer than C programs
108through a dataflow tracing mechanism which prevents many stupid
109security holes.
110
111If you have a problem that would ordinarily use B<sed> or B<awk> or
112B<sh>, but it exceeds their capabilities or must run a little faster,
113and you don't want to write the silly thing in C, then Perl may be for
114you. There are also translators to turn your B<sed> and B<awk>
115scripts into Perl scripts.
a0d0e21e
LW
116
117But wait, there's more...
118
119Perl version 5 is nearly a complete rewrite, and provides
120the following additional benefits:
121
122=over 5
123
124=item * Many usability enhancements
125
126It is now possible to write much more readable Perl code (even within
127regular expressions). Formerly cryptic variable names can be replaced
128by mnemonic identifiers. Error messages are more informative, and the
129optional warnings will catch many of the mistakes a novice might make.
130This cannot be stressed enough. Whenever you get mysterious behavior,
131try the B<-w> switch!!! Whenever you don't get mysterious behavior,
132try using B<-w> anyway.
133
134=item * Simplified grammar
135
136The new yacc grammar is one half the size of the old one. Many of the
137arbitrary grammar rules have been regularized. The number of reserved
138words has been cut by 2/3. Despite this, nearly all old Perl scripts
139will continue to work unchanged.
140
141=item * Lexical scoping
142
143Perl variables may now be declared within a lexical scope, like "auto"
144variables in C. Not only is this more efficient, but it contributes
5f05dabc
PP
145to better privacy for "programming in the large". Anonymous
146subroutines exhibit deep binding of lexical variables (closures).
a0d0e21e
LW
147
148=item * Arbitrarily nested data structures
149
150Any scalar value, including any array element, may now contain a
151reference to any other variable or subroutine. You can easily create
152anonymous variables and subroutines. Perl manages your reference
153counts for you.
154
155=item * Modularity and reusability
156
157The Perl library is now defined in terms of modules which can be easily
158shared among various packages. A package may choose to import all or a
159portion of a module's published interface. Pragmas (that is, compiler
160directives) are defined and used by the same mechanism.
161
162=item * Object-oriented programming
163
164A package can function as a class. Dynamic multiple inheritance and
165virtual methods are supported in a straightforward manner and with very
166little new syntax. Filehandles may now be treated as objects.
167
c07a80fd 168=item * Embeddable and Extensible
a0d0e21e
LW
169
170Perl may now be embedded easily in your C or C++ application, and can
171either call or be called by your routines through a documented
172interface. The XS preprocessor is provided to make it easy to glue
173your C or C++ routines into Perl. Dynamic loading of modules is
5f05dabc 174supported, and Perl itself can be made into a dynamic library.
a0d0e21e
LW
175
176=item * POSIX compliant
177
178A major new module is the POSIX module, which provides access to all
179available POSIX routines and definitions, via object classes where
180appropriate.
181
182=item * Package constructors and destructors
183
184The new BEGIN and END blocks provide means to capture control as
185a package is being compiled, and after the program exits. As a
186degenerate case they work just like awk's BEGIN and END when you
187use the B<-p> or B<-n> switches.
188
189=item * Multiple simultaneous DBM implementations
190
191A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
192files from the same script simultaneously. In fact, the old dbmopen
193interface has been generalized to allow any variable to be tied
194to an object class which defines its access methods.
195
196=item * Subroutine definitions may now be autoloaded
197
198In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
5f05dabc 199semantics for undefined subroutine calls. It's not for just autoloading.
a0d0e21e
LW
200
201=item * Regular expression enhancements
202
203You can now specify non-greedy quantifiers. You can now do grouping
204without creating a backreference. You can now write regular expressions
205with embedded whitespace and comments for readability. A consistent
206extensibility mechanism has been added that is upwardly compatible with
207all old regular expressions.
208
5f05dabc
PP
209=item * Innumerable Unbundled Modules
210
211The Comprehensive Perl Archive Network described in L<perlmod>
212contains hundreds of plug-and-play modules full of reusable
213code. See F<http://www.perl.com/CPAN> for a site near you.
214
215=item * Compilability
216
217While not yet in full production mode, a working perl-to-C compiler
218does exist. It can generate portable bytecode, simple C, or
219optimized C code.
220
a0d0e21e
LW
221=back
222
68dc0745 223Okay, that's I<definitely> enough hype.
a0d0e21e
LW
224
225=head1 ENVIRONMENT
226
1e422769 227See L<perlrun>.
a0d0e21e
LW
228
229=head1 AUTHOR
230
9607fc9c 231Larry Wall <F<larry@wall.org>>, with the help of oodles of other folks.
a0d0e21e
LW
232
233=head1 FILES
234
235 "/tmp/perl-e$$" temporary file for -e commands
5f05dabc 236 "@INC" locations of perl libraries
a0d0e21e
LW
237
238=head1 SEE ALSO
239
240 a2p awk to perl translator
4633a7c4 241
a0d0e21e
LW
242 s2p sed to perl translator
243
244=head1 DIAGNOSTICS
245
246The B<-w> switch produces some lovely diagnostics.
247
248See L<perldiag> for explanations of all Perl's diagnostics.
249
250Compilation errors will tell you the line number of the error, with an
251indication of the next token or token type that was to be examined.
252(In the case of a script passed to Perl via B<-e> switches, each
253B<-e> is counted as one line.)
254
255Setuid scripts have additional constraints that can produce error
256messages such as "Insecure dependency". See L<perlsec>.
257
258Did we mention that you should definitely consider using the B<-w>
259switch?
260
261=head1 BUGS
262
263The B<-w> switch is not mandatory.
264
265Perl is at the mercy of your machine's definitions of various
5f05dabc
PP
266operations such as type casting, atof(), and sprintf(). The latter
267can even trigger a core dump when passed ludicrous input values.
a0d0e21e 268
748a9306 269If your stdio requires a seek or eof between reads and writes on a
a0d0e21e
LW
270particular stream, so does Perl. (This doesn't apply to sysread()
271and syswrite().)
272
273While none of the built-in data types have any arbitrary size limits
274(apart from memory size), there are still a few arbitrary limits: a
d357d931 275given variable name may not be longer than 255 characters, and no
a0d0e21e
LW
276component of your PATH may be longer than 255 if you use B<-S>. A regular
277expression may not compile to more than 32767 bytes internally.
278
b0607b7a
LV
279You may mail your bug reports (be sure to include full configuration
280information as output by the myconfig program in the perl source tree,
9607fc9c 281or by C<perl -V>) to <F<perlbug@perl.com>>.
c07a80fd
PP
282If you've succeeded in compiling perl, the perlbug script in the utils/
283subdirectory can be used to help mail in a bug report.
4633a7c4 284
a0d0e21e
LW
285Perl actually stands for Pathologically Eclectic Rubbish Lister, but
286don't tell anyone I said that.
287
288=head1 NOTES
289
290The Perl motto is "There's more than one way to do it." Divining
291how many more is left as an exercise to the reader.
292
4633a7c4 293The three principal virtues of a programmer are Laziness,
a0d0e21e 294Impatience, and Hubris. See the Camel Book for why.
16d20bd9 295