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