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
33 perlmod Perl modules: how they work
34 perlmodlib Perl modules: how to write and use
36 perllocale Perl locale support
38 perlref Perl references
39 perldsc Perl data structures intro
40 perllol Perl data structures: lists of lists
41 perltoot Perl OO tutorial
43 perltie Perl objects hidden behind simple variables
44 perlbot Perl OO tricks and examples
45 perlipc Perl interprocess communication
47 perldebug Perl debugging
48 perldiag Perl diagnostic messages
50 perltrap Perl traps for the unwary
51 perlstyle Perl style guide
53 perlpod Perl plain old documentation
54 perlbook Perl book information
56 perlembed Perl ways to embed perl in your C or C++ application
57 perlapio Perl internal IO abstraction interface
58 perlxs Perl XS application programming interface
59 perlxstut Perl XS tutorial
60 perlguts Perl internal functions for those doing extensions
61 perlcall Perl calling conventions from C
63 (If you're intending to read these straight through for the first time,
64 the suggested order will tend to reduce the number of forward references.)
66 By default, all of the above manpages are installed in the
67 F</usr/local/man/> directory.
69 Extensive additional documentation for Perl modules is available. The
70 default configuration for perl will place this additional documentation
71 in the F</usr/local/lib/perl5/man> directory (or else in the F<man>
72 subdirectory of the Perl library directory). Some of this additional
73 documentation is distributed standard with Perl, but you'll also find
74 documentation for third-party modules there.
76 You should be able to view Perl's documentation with your man(1)
77 program by including the proper directories in the appropriate start-up
78 files, or in the MANPATH environment variable. To find out where the
79 configuration has installed the manpages, type:
83 If the directories have a common stem, such as F</usr/local/man/man1>
84 and F</usr/local/man/man3>, you need only to add that stem
85 (F</usr/local/man>) to your man(1) configuration files or your MANPATH
86 environment variable. If they do not share a stem, you'll have to add
89 If that doesn't work for some reason, you can still use the
90 supplied F<perldoc> script to view module information. You might
91 also look into getting a replacement man program.
93 If something strange has gone wrong with your program and you're not
94 sure where you should look for help, try the B<-w> switch first. It
95 will often point out exactly where the trouble is.
99 Perl is a language optimized for scanning arbitrary
100 text files, extracting information from those text files, and printing
101 reports based on that information. It's also a good language for many
102 system management tasks. The language is intended to be practical
103 (easy to use, efficient, complete) rather than beautiful (tiny,
106 Perl combines (in the author's opinion, anyway) some of the best
107 features of C, B<sed>, B<awk>, and B<sh>, so people familiar with
108 those languages should have little difficulty with it. (Language
109 historians will also note some vestiges of B<csh>, Pascal, and even
110 BASIC-PLUS.) Expression syntax corresponds quite closely to C
111 expression syntax. Unlike most Unix utilities, Perl does not
112 arbitrarily limit the size of your data--if you've got the memory,
113 Perl can slurp in your whole file as a single string. Recursion is of
114 unlimited depth. And the tables used by hashes (previously called
115 "associative arrays") grow as necessary to prevent degraded
116 performance. Perl uses sophisticated pattern matching techniques to
117 scan large amounts of data very quickly. Although optimized for
118 scanning text, Perl can also deal with binary data, and can make dbm
119 files look like hashes. Setuid Perl scripts are safer than C programs
120 through a dataflow tracing mechanism which prevents many stupid
123 If you have a problem that would ordinarily use B<sed> or B<awk> or
124 B<sh>, but it exceeds their capabilities or must run a little faster,
125 and you don't want to write the silly thing in C, then Perl may be for
126 you. There are also translators to turn your B<sed> and B<awk>
127 scripts into Perl scripts.
129 But wait, there's more...
131 Perl version 5 is nearly a complete rewrite, and provides
132 the following additional benefits:
136 =item * Many usability enhancements
138 It is now possible to write much more readable Perl code (even within
139 regular expressions). Formerly cryptic variable names can be replaced
140 by mnemonic identifiers. Error messages are more informative, and the
141 optional warnings will catch many of the mistakes a novice might make.
142 This cannot be stressed enough. Whenever you get mysterious behavior,
143 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
144 try using B<-w> anyway.
146 =item * Simplified grammar
148 The new yacc grammar is one half the size of the old one. Many of the
149 arbitrary grammar rules have been regularized. The number of reserved
150 words has been cut by 2/3. Despite this, nearly all old Perl scripts
151 will continue to work unchanged.
153 =item * Lexical scoping
155 Perl variables may now be declared within a lexical scope, like "auto"
156 variables in C. Not only is this more efficient, but it contributes
157 to better privacy for "programming in the large". Anonymous
158 subroutines exhibit deep binding of lexical variables (closures).
160 =item * Arbitrarily nested data structures
162 Any scalar value, including any array element, may now contain a
163 reference to any other variable or subroutine. You can easily create
164 anonymous variables and subroutines. Perl manages your reference
167 =item * Modularity and reusability
169 The Perl library is now defined in terms of modules which can be easily
170 shared among various packages. A package may choose to import all or a
171 portion of a module's published interface. Pragmas (that is, compiler
172 directives) are defined and used by the same mechanism.
174 =item * Object-oriented programming
176 A package can function as a class. Dynamic multiple inheritance and
177 virtual methods are supported in a straightforward manner and with very
178 little new syntax. Filehandles may now be treated as objects.
180 =item * Embeddable and Extensible
182 Perl may now be embedded easily in your C or C++ application, and can
183 either call or be called by your routines through a documented
184 interface. The XS preprocessor is provided to make it easy to glue
185 your C or C++ routines into Perl. Dynamic loading of modules is
186 supported, and Perl itself can be made into a dynamic library.
188 =item * POSIX compliant
190 A major new module is the POSIX module, which provides access to all
191 available POSIX routines and definitions, via object classes where
194 =item * Package constructors and destructors
196 The new BEGIN and END blocks provide means to capture control as
197 a package is being compiled, and after the program exits. As a
198 degenerate case they work just like awk's BEGIN and END when you
199 use the B<-p> or B<-n> switches.
201 =item * Multiple simultaneous DBM implementations
203 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
204 files from the same script simultaneously. In fact, the old dbmopen
205 interface has been generalized to allow any variable to be tied
206 to an object class which defines its access methods.
208 =item * Subroutine definitions may now be autoloaded
210 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
211 semantics for undefined subroutine calls. It's not for just autoloading.
213 =item * Regular expression enhancements
215 You can now specify nongreedy quantifiers. You can now do grouping
216 without creating a backreference. You can now write regular expressions
217 with embedded whitespace and comments for readability. A consistent
218 extensibility mechanism has been added that is upwardly compatible with
219 all old regular expressions.
221 =item * Innumerable Unbundled Modules
223 The Comprehensive Perl Archive Network described in L<perlmodlib>
224 contains hundreds of plug-and-play modules full of reusable code.
225 See F<http://www.perl.com/CPAN> for a site near you.
227 =item * Compilability
229 While not yet in full production mode, a working perl-to-C compiler
230 does exist. It can generate portable byte code, simple C, or
235 Okay, that's I<definitely> enough hype.
243 Larry Wall <F<larry@wall.org>>, with the help of oodles of other folks.
247 "/tmp/perl-e$$" temporary file for -e commands
248 "@INC" locations of perl libraries
252 a2p awk to perl translator
254 s2p sed to perl translator
258 The B<-w> switch produces some lovely diagnostics.
260 See L<perldiag> for explanations of all Perl's diagnostics.
262 Compilation errors will tell you the line number of the error, with an
263 indication of the next token or token type that was to be examined.
264 (In the case of a script passed to Perl via B<-e> switches, each
265 B<-e> is counted as one line.)
267 Setuid scripts have additional constraints that can produce error
268 messages such as "Insecure dependency". See L<perlsec>.
270 Did we mention that you should definitely consider using the B<-w>
275 The B<-w> switch is not mandatory.
277 Perl is at the mercy of your machine's definitions of various
278 operations such as type casting, atof(), and floating-point
279 output with sprintf().
281 If your stdio requires a seek or eof between reads and writes on a
282 particular stream, so does Perl. (This doesn't apply to sysread()
285 While none of the built-in data types have any arbitrary size limits
286 (apart from memory size), there are still a few arbitrary limits: a
287 given variable name may not be longer than 255 characters, and no
288 component of your PATH may be longer than 255 if you use B<-S>. A regular
289 expression may not compile to more than 32767 bytes internally.
291 You may mail your bug reports (be sure to include full configuration
292 information as output by the myconfig program in the perl source tree,
293 or by C<perl -V>) to <F<perlbug@perl.com>>.
294 If you've succeeded in compiling perl, the perlbug script in the utils/
295 subdirectory can be used to help mail in a bug report.
297 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
298 don't tell anyone I said that.
302 The Perl motto is "There's more than one way to do it." Divining
303 how many more is left as an exercise to the reader.
305 The three principal virtues of a programmer are Laziness,
306 Impatience, and Hubris. See the Camel Book for why.