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