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 ways to embed perl in your C or C++ application
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 By default, all of the above manpages are installed in the
66 F</usr/local/man/> directory.
68 Extensive additional documentation for Perl modules is available. The
69 default configuration for perl will place this additional documentation
70 in the F</usr/local/lib/perl5/man> directory (or else in the F<man>
71 subdirectory of the Perl library directory). Some of this additional
72 documentation is distributed standard with Perl, but you'll also find
73 documentation for third-party modules there.
75 You should be able to view Perl's documentation with your man(1)
76 program by including the proper directories in the appropriate start-up
77 files, or in the MANPATH environment variable. To find out where the
78 configuration has installed the manpages, type:
82 If the directories have a common stem, such as F</usr/local/man/man1>
83 and F</usr/local/man/man3>, you need only to add that stem
84 (F</usr/local/man>) to your man(1) configuration files or your MANPATH
85 environment variable. If they do not share a stem, you'll have to add
88 If that doesn't work for some reason, you can still use the
89 supplied F<perldoc> script to view module information. You might
90 also look into getting a replacement man program.
92 If something strange has gone wrong with your program and you're not
93 sure where you should look for help, try the B<-w> switch first. It
94 will often point out exactly where the trouble is.
98 Perl is a language optimized for scanning arbitrary
99 text files, extracting information from those text files, and printing
100 reports based on that information. It's also a good language for many
101 system management tasks. The language is intended to be practical
102 (easy to use, efficient, complete) rather than beautiful (tiny,
105 Perl combines (in the author's opinion, anyway) some of the best
106 features of C, B<sed>, B<awk>, and B<sh>, so people familiar with
107 those languages should have little difficulty with it. (Language
108 historians will also note some vestiges of B<csh>, Pascal, and even
109 BASIC-PLUS.) Expression syntax corresponds quite closely to C
110 expression syntax. Unlike most Unix utilities, Perl does not
111 arbitrarily limit the size of your data--if you've got the memory,
112 Perl can slurp in your whole file as a single string. Recursion is of
113 unlimited depth. And the tables used by hashes (previously called
114 "associative arrays") grow as necessary to prevent degraded
115 performance. Perl uses sophisticated pattern matching techniques to
116 scan large amounts of data very quickly. Although optimized for
117 scanning text, Perl can also deal with binary data, and can make dbm
118 files look like hashes. Setuid Perl scripts are safer than C programs
119 through a dataflow tracing mechanism which prevents many stupid
122 If you have a problem that would ordinarily use B<sed> or B<awk> or
123 B<sh>, but it exceeds their capabilities or must run a little faster,
124 and you don't want to write the silly thing in C, then Perl may be for
125 you. There are also translators to turn your B<sed> and B<awk>
126 scripts into Perl scripts.
128 But wait, there's more...
130 Perl version 5 is nearly a complete rewrite, and provides
131 the following additional benefits:
135 =item * Many usability enhancements
137 It is now possible to write much more readable Perl code (even within
138 regular expressions). Formerly cryptic variable names can be replaced
139 by mnemonic identifiers. Error messages are more informative, and the
140 optional warnings will catch many of the mistakes a novice might make.
141 This cannot be stressed enough. Whenever you get mysterious behavior,
142 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
143 try using B<-w> anyway.
145 =item * Simplified grammar
147 The new yacc grammar is one half the size of the old one. Many of the
148 arbitrary grammar rules have been regularized. The number of reserved
149 words has been cut by 2/3. Despite this, nearly all old Perl scripts
150 will continue to work unchanged.
152 =item * Lexical scoping
154 Perl variables may now be declared within a lexical scope, like "auto"
155 variables in C. Not only is this more efficient, but it contributes
156 to better privacy for "programming in the large". Anonymous
157 subroutines exhibit deep binding of lexical variables (closures).
159 =item * Arbitrarily nested data structures
161 Any scalar value, including any array element, may now contain a
162 reference to any other variable or subroutine. You can easily create
163 anonymous variables and subroutines. Perl manages your reference
166 =item * Modularity and reusability
168 The Perl library is now defined in terms of modules which can be easily
169 shared among various packages. A package may choose to import all or a
170 portion of a module's published interface. Pragmas (that is, compiler
171 directives) are defined and used by the same mechanism.
173 =item * Object-oriented programming
175 A package can function as a class. Dynamic multiple inheritance and
176 virtual methods are supported in a straightforward manner and with very
177 little new syntax. Filehandles may now be treated as objects.
179 =item * Embeddable and Extensible
181 Perl may now be embedded easily in your C or C++ application, and can
182 either call or be called by your routines through a documented
183 interface. The XS preprocessor is provided to make it easy to glue
184 your C or C++ routines into Perl. Dynamic loading of modules is
185 supported, and Perl itself can be made into a dynamic library.
187 =item * POSIX compliant
189 A major new module is the POSIX module, which provides access to all
190 available POSIX routines and definitions, via object classes where
193 =item * Package constructors and destructors
195 The new BEGIN and END blocks provide means to capture control as
196 a package is being compiled, and after the program exits. As a
197 degenerate case they work just like awk's BEGIN and END when you
198 use the B<-p> or B<-n> switches.
200 =item * Multiple simultaneous DBM implementations
202 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
203 files from the same script simultaneously. In fact, the old dbmopen
204 interface has been generalized to allow any variable to be tied
205 to an object class which defines its access methods.
207 =item * Subroutine definitions may now be autoloaded
209 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
210 semantics for undefined subroutine calls. It's not for just autoloading.
212 =item * Regular expression enhancements
214 You can now specify nongreedy quantifiers. You can now do grouping
215 without creating a backreference. You can now write regular expressions
216 with embedded whitespace and comments for readability. A consistent
217 extensibility mechanism has been added that is upwardly compatible with
218 all old regular expressions.
220 =item * Innumerable Unbundled Modules
222 The Comprehensive Perl Archive Network described in L<perlmod>
223 contains hundreds of plug-and-play modules full of reusable
224 code. See F<http://www.perl.com/CPAN> for a site near you.
226 =item * Compilability
228 While not yet in full production mode, a working perl-to-C compiler
229 does exist. It can generate portable byte code, simple C, or
234 Okay, that's I<definitely> enough hype.
242 Larry Wall <F<larry@wall.org>>, with the help of oodles of other folks.
246 "/tmp/perl-e$$" temporary file for -e commands
247 "@INC" locations of perl libraries
251 a2p awk to perl translator
253 s2p sed to perl translator
257 The B<-w> switch produces some lovely diagnostics.
259 See L<perldiag> for explanations of all Perl's diagnostics.
261 Compilation errors will tell you the line number of the error, with an
262 indication of the next token or token type that was to be examined.
263 (In the case of a script passed to Perl via B<-e> switches, each
264 B<-e> is counted as one line.)
266 Setuid scripts have additional constraints that can produce error
267 messages such as "Insecure dependency". See L<perlsec>.
269 Did we mention that you should definitely consider using the B<-w>
274 The B<-w> switch is not mandatory.
276 Perl is at the mercy of your machine's definitions of various
277 operations such as type casting, atof(), and sprintf(). The latter
278 can even trigger a core dump when passed ludicrous input values.
280 If your stdio requires a seek or eof between reads and writes on a
281 particular stream, so does Perl. (This doesn't apply to sysread()
284 While none of the built-in data types have any arbitrary size limits
285 (apart from memory size), there are still a few arbitrary limits: a
286 given variable name may not be longer than 255 characters, and no
287 component of your PATH may be longer than 255 if you use B<-S>. A regular
288 expression may not compile to more than 32767 bytes internally.
290 You may mail your bug reports (be sure to include full configuration
291 information as output by the myconfig program in the perl source tree,
292 or by C<perl -V>) to <F<perlbug@perl.com>>.
293 If you've succeeded in compiling perl, the perlbug script in the utils/
294 subdirectory can be used to help mail in a bug report.
296 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
297 don't tell anyone I said that.
301 The Perl motto is "There's more than one way to do it." Divining
302 how many more is left as an exercise to the reader.
304 The three principal virtues of a programmer are Laziness,
305 Impatience, and Hubris. See the Camel Book for why.