3 perl - Practical Extraction and Report Language
7 B<perl> [ B<-acdhnpPsSTuUvw> ]
9 [ S<B<-D>I<number/list>]> ]
11 [ S<B<-i>[I<extension>]> ]
15 [ I<programfile> | S<B<-e> I<command>> ]
18 For ease of access, the Perl manual has been split up into a number
21 perl Perl overview (this section)
22 perltoc Perl documentation table of contents
23 perldata Perl data structures
25 perlop Perl operators and precedence
26 perlre Perl regular expressions
27 perlrun Perl execution and options
28 perlfunc Perl builtin functions
29 perlvar Perl predefined variables
30 perlsub Perl subroutines
32 perlref Perl references
33 perldsc Perl data structures intro
34 perllol Perl data structures: lists of lists
36 perltie Perl objects hidden behind simple variables
37 perlbot Perl OO tricks and examples
38 perldebug Perl debugging
39 perldiag Perl diagnostic messages
41 perlipc Perl interprocess communication
43 perltrap Perl traps for the unwary
44 perlstyle Perl style guide
45 perlxs Perl XS application programming interface
46 perlxstut Perl XS tutorial
47 perlguts Perl internal functions for those doing extensions
48 perlcall Perl calling conventions from C
49 perlembed Perl how to embed perl in your C or C++ app
50 perlpod Perl plain old documentation
51 perlbook Perl book information
53 (If you're intending to read these straight through for the first time,
54 the suggested order will tend to reduce the number of forward references.)
56 Additional documentation for Perl modules is available in the
57 F</usr/local/man/> directory. Some of this is distributed standard with
58 Perl, but you'll also find third-party modules there. You should be able
59 to view this with your man(1) program by including the proper directories
60 in the appropriate start-up files. To find out where these are, type:
62 perl -le 'use Config; print "@Config{man1dir,man3dir}"'
64 If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
65 you would only need to add F</usr/local/man> to your MANPATH. If
66 they are different, you'll have to add both stems.
68 If that doesn't work for some reason, you can still use the
69 supplied F<perldoc> script to view module information. You might
70 also look into getting a replacement man program.
72 If something strange has gone wrong with your program and you're not
73 sure where you should look for help, try the B<-w> switch first. It
74 will often point out exactly where the trouble is.
78 Perl is an interpreted language optimized for scanning arbitrary
79 text files, extracting information from those text files, and printing
80 reports based on that information. It's also a good language for many
81 system management tasks. The language is intended to be practical
82 (easy to use, efficient, complete) rather than beautiful (tiny,
83 elegant, minimal). It combines (in the author's opinion, anyway) some
84 of the best features of C, B<sed>, B<awk>, and B<sh>, so people
85 familiar with those languages should have little difficulty with it.
86 (Language historians will also note some vestiges of B<csh>, Pascal,
87 and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
88 expression syntax. Unlike most Unix utilities, Perl does not
89 arbitrarily limit the size of your data--if you've got the memory,
90 Perl can slurp in your whole file as a single string. Recursion is
91 of unlimited depth. And the hash tables used by associative arrays
92 grow as necessary to prevent degraded performance. Perl uses
93 sophisticated pattern matching techniques to scan large amounts of data
94 very quickly. Although optimized for scanning text, Perl can also
95 deal with binary data, and can make dbm files look like associative
96 arrays. Setuid Perl scripts are safer than
97 C programs through a dataflow tracing mechanism which prevents many
98 stupid security holes. If you have a problem that would ordinarily use
99 B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
100 run a little faster, and you don't want to write the silly thing in C,
101 then Perl may be for you. There are also translators to turn your
102 B<sed> and B<awk> scripts into Perl scripts.
104 But wait, there's more...
106 Perl version 5 is nearly a complete rewrite, and provides
107 the following additional benefits:
111 =item * Many usability enhancements
113 It is now possible to write much more readable Perl code (even within
114 regular expressions). Formerly cryptic variable names can be replaced
115 by mnemonic identifiers. Error messages are more informative, and the
116 optional warnings will catch many of the mistakes a novice might make.
117 This cannot be stressed enough. Whenever you get mysterious behavior,
118 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
119 try using B<-w> anyway.
121 =item * Simplified grammar
123 The new yacc grammar is one half the size of the old one. Many of the
124 arbitrary grammar rules have been regularized. The number of reserved
125 words has been cut by 2/3. Despite this, nearly all old Perl scripts
126 will continue to work unchanged.
128 =item * Lexical scoping
130 Perl variables may now be declared within a lexical scope, like "auto"
131 variables in C. Not only is this more efficient, but it contributes
132 to better privacy for "programming in the large".
134 =item * Arbitrarily nested data structures
136 Any scalar value, including any array element, may now contain a
137 reference to any other variable or subroutine. You can easily create
138 anonymous variables and subroutines. Perl manages your reference
141 =item * Modularity and reusability
143 The Perl library is now defined in terms of modules which can be easily
144 shared among various packages. A package may choose to import all or a
145 portion of a module's published interface. Pragmas (that is, compiler
146 directives) are defined and used by the same mechanism.
148 =item * Object-oriented programming
150 A package can function as a class. Dynamic multiple inheritance and
151 virtual methods are supported in a straightforward manner and with very
152 little new syntax. Filehandles may now be treated as objects.
154 =item * Embeddable and Extensible
156 Perl may now be embedded easily in your C or C++ application, and can
157 either call or be called by your routines through a documented
158 interface. The XS preprocessor is provided to make it easy to glue
159 your C or C++ routines into Perl. Dynamic loading of modules is
162 =item * POSIX compliant
164 A major new module is the POSIX module, which provides access to all
165 available POSIX routines and definitions, via object classes where
168 =item * Package constructors and destructors
170 The new BEGIN and END blocks provide means to capture control as
171 a package is being compiled, and after the program exits. As a
172 degenerate case they work just like awk's BEGIN and END when you
173 use the B<-p> or B<-n> switches.
175 =item * Multiple simultaneous DBM implementations
177 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
178 files from the same script simultaneously. In fact, the old dbmopen
179 interface has been generalized to allow any variable to be tied
180 to an object class which defines its access methods.
182 =item * Subroutine definitions may now be autoloaded
184 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
185 semantics for undefined subroutine calls. It's not just for autoloading.
187 =item * Regular expression enhancements
189 You can now specify non-greedy quantifiers. You can now do grouping
190 without creating a backreference. You can now write regular expressions
191 with embedded whitespace and comments for readability. A consistent
192 extensibility mechanism has been added that is upwardly compatible with
193 all old regular expressions.
197 Ok, that's I<definitely> enough hype.
205 Used if chdir has no argument.
209 Used if chdir has no argument and HOME is not set.
213 Used in executing subprocesses, and in finding the script if B<-S> is
218 A colon-separated list of directories in which to look for Perl library
219 files before looking in the standard library and the current
220 directory. If PERL5LIB is not defined, PERLLIB is used. When running
221 taint checks (because the script was running setuid or setgid, or the
222 B<-T> switch was used), neither variable is used. The script should
225 use lib "/my/directory";
229 The command used to get the debugger code. If unset, uses
231 BEGIN { require 'perl5db.pl' }
235 A colon-separated list of directories in which to look for Perl library
236 files before looking in the standard library and the current
237 directory. If PERL5LIB is defined, PERLLIB is not used.
241 Apart from these, Perl uses no other environment variables, except
242 to make them available to the script being executed, and to child
243 processes. However, scripts running setuid would do well to execute
244 the following lines before doing anything else, just to keep people
247 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
248 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
249 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
253 Larry Wall E<lt><F<lwall@sems.com>E<gt>, with the help of oodles of other folks.
257 "/tmp/perl-e$$" temporary file for -e commands
258 "@INC" locations of perl 5 libraries
262 a2p awk to perl translator
264 s2p sed to perl translator
268 The B<-w> switch produces some lovely diagnostics.
270 See L<perldiag> for explanations of all Perl's diagnostics.
272 Compilation errors will tell you the line number of the error, with an
273 indication of the next token or token type that was to be examined.
274 (In the case of a script passed to Perl via B<-e> switches, each
275 B<-e> is counted as one line.)
277 Setuid scripts have additional constraints that can produce error
278 messages such as "Insecure dependency". See L<perlsec>.
280 Did we mention that you should definitely consider using the B<-w>
285 The B<-w> switch is not mandatory.
287 Perl is at the mercy of your machine's definitions of various
288 operations such as type casting, atof() and sprintf(). The latter
289 can even trigger a coredump when passed ludicrous input values.
291 If your stdio requires a seek or eof between reads and writes on a
292 particular stream, so does Perl. (This doesn't apply to sysread()
295 While none of the built-in data types have any arbitrary size limits
296 (apart from memory size), there are still a few arbitrary limits: a
297 given identifier may not be longer than 255 characters, and no
298 component of your PATH may be longer than 255 if you use B<-S>. A regular
299 expression may not compile to more than 32767 bytes internally.
301 See the perl bugs database at F<http://perl.com/perl/bugs/>. You may
302 mail your bug reports (be sure to include full configuration information
303 as output by the myconfig program in the perl source tree) to
305 If you've succeeded in compiling perl, the perlbug script in the utils/
306 subdirectory can be used to help mail in a bug report.
308 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
309 don't tell anyone I said that.
313 The Perl motto is "There's more than one way to do it." Divining
314 how many more is left as an exercise to the reader.
316 The three principal virtues of a programmer are Laziness,
317 Impatience, and Hubris. See the Camel Book for why.