3 perl - Practical Extraction and Report Language
7 For ease of access, the Perl manual has been split up into a number
10 perl Perl overview (this section)
11 perltoc Perl documentation table of contents
12 perldata Perl data structures
14 perlop Perl operators and precedence
15 perlre Perl regular expressions
16 perlrun Perl execution and options
17 perlfunc Perl builtin functions
18 perlvar Perl predefined variables
19 perlsub Perl subroutines
21 perlref Perl references
22 perldsc Perl data structures intro
23 perllol Perl data structures: lists of lists
25 perltie Perl objects hidden behind simple variables
26 perlbot Perl OO tricks and examples
27 perldebug Perl debugging
28 perldiag Perl diagnostic messages
30 perlipc Perl interprocess communication
32 perltrap Perl traps for the unwary
33 perlstyle Perl style guide
34 perlxs Perl XS application programming interface
35 perlxstut Perl XS tutorial
36 perlguts Perl internal functions for those doing extensions
37 perlcall Perl calling conventions from C
38 perlembed Perl how to embed perl in your C or C++ app
39 perlpod Perl plain old documentation
40 perlbook Perl book information
42 (If you're intending to read these straight through for the first time,
43 the suggested order will tend to reduce the number of forward references.)
45 Additional documentation for Perl modules is available in the
46 F</usr/local/man/> directory. Some of this is distributed standard with
47 Perl, but you'll also find third-party modules there. You should be able
48 to view this with your man(1) program by including the proper directories
49 in the appropriate start-up files. To find out where these are, type:
51 perl -le 'use Config; print "@Config{man1dir,man3dir}"'
53 If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
54 you would only need to add F</usr/local/man> to your MANPATH. If
55 they are different, you'll have to add both stems.
57 If that doesn't work for some reason, you can still use the
58 supplied F<perldoc> script to view module information. You might
59 also look into getting a replacement man program.
61 If something strange has gone wrong with your program and you're not
62 sure where you should look for help, try the B<-w> switch first. It
63 will often point out exactly where the trouble is.
67 Perl is an interpreted language optimized for scanning arbitrary
68 text files, extracting information from those text files, and printing
69 reports based on that information. It's also a good language for many
70 system management tasks. The language is intended to be practical
71 (easy to use, efficient, complete) rather than beautiful (tiny,
72 elegant, minimal). It combines (in the author's opinion, anyway) some
73 of the best features of C, B<sed>, B<awk>, and B<sh>, so people
74 familiar with those languages should have little difficulty with it.
75 (Language historians will also note some vestiges of B<csh>, Pascal,
76 and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
77 expression syntax. Unlike most Unix utilities, Perl does not
78 arbitrarily limit the size of your data--if you've got the memory,
79 Perl can slurp in your whole file as a single string. Recursion is
80 of unlimited depth. And the hash tables used by associative arrays
81 grow as necessary to prevent degraded performance. Perl uses
82 sophisticated pattern matching techniques to scan large amounts of data
83 very quickly. Although optimized for scanning text, Perl can also
84 deal with binary data, and can make dbm files look like associative
85 arrays (where dbm is available). Setuid Perl scripts are safer than
86 C programs through a dataflow tracing mechanism which prevents many
87 stupid security holes. If you have a problem that would ordinarily use
88 B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
89 run a little faster, and you don't want to write the silly thing in C,
90 then Perl may be for you. There are also translators to turn your
91 B<sed> and B<awk> scripts into Perl scripts.
93 But wait, there's more...
95 Perl version 5 is nearly a complete rewrite, and provides
96 the following additional benefits:
100 =item * Many usability enhancements
102 It is now possible to write much more readable Perl code (even within
103 regular expressions). Formerly cryptic variable names can be replaced
104 by mnemonic identifiers. Error messages are more informative, and the
105 optional warnings will catch many of the mistakes a novice might make.
106 This cannot be stressed enough. Whenever you get mysterious behavior,
107 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
108 try using B<-w> anyway.
110 =item * Simplified grammar
112 The new yacc grammar is one half the size of the old one. Many of the
113 arbitrary grammar rules have been regularized. The number of reserved
114 words has been cut by 2/3. Despite this, nearly all old Perl scripts
115 will continue to work unchanged.
117 =item * Lexical scoping
119 Perl variables may now be declared within a lexical scope, like "auto"
120 variables in C. Not only is this more efficient, but it contributes
121 to better privacy for "programming in the large".
123 =item * Arbitrarily nested data structures
125 Any scalar value, including any array element, may now contain a
126 reference to any other variable or subroutine. You can easily create
127 anonymous variables and subroutines. Perl manages your reference
130 =item * Modularity and reusability
132 The Perl library is now defined in terms of modules which can be easily
133 shared among various packages. A package may choose to import all or a
134 portion of a module's published interface. Pragmas (that is, compiler
135 directives) are defined and used by the same mechanism.
137 =item * Object-oriented programming
139 A package can function as a class. Dynamic multiple inheritance and
140 virtual methods are supported in a straightforward manner and with very
141 little new syntax. Filehandles may now be treated as objects.
143 =item * Embeddible and Extensible
145 Perl may now be embedded easily in your C or C++ application, and can
146 either call or be called by your routines through a documented
147 interface. The XS preprocessor is provided to make it easy to glue
148 your C or C++ routines into Perl. Dynamic loading of modules is
151 =item * POSIX compliant
153 A major new module is the POSIX module, which provides access to all
154 available POSIX routines and definitions, via object classes where
157 =item * Package constructors and destructors
159 The new BEGIN and END blocks provide means to capture control as
160 a package is being compiled, and after the program exits. As a
161 degenerate case they work just like awk's BEGIN and END when you
162 use the B<-p> or B<-n> switches.
164 =item * Multiple simultaneous DBM implementations
166 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
167 files from the same script simultaneously. In fact, the old dbmopen
168 interface has been generalized to allow any variable to be tied
169 to an object class which defines its access methods.
171 =item * Subroutine definitions may now be autoloaded
173 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
174 semantics for undefined subroutine calls. It's not just for autoloading.
176 =item * Regular expression enhancements
178 You can now specify non-greedy quantifiers. You can now do grouping
179 without creating a backreference. You can now write regular expressions
180 with embedded whitespace and comments for readability. A consistent
181 extensibility mechanism has been added that is upwardly compatible with
182 all old regular expressions.
186 Ok, that's I<definitely> enough hype.
194 Used if chdir has no argument.
198 Used if chdir has no argument and HOME is not set.
202 Used in executing subprocesses, and in finding the script if B<-S> is
207 A colon-separated list of directories in which to look for Perl library
208 files before looking in the standard library and the current
209 directory. If PERL5LIB is not defined, PERLLIB is used. When running
210 taint checks (because the script was running setuid or setgid, or the
211 B<-T> switch was used), neither variable is used. The script should
214 use lib "/my/directory";
218 The command used to get the debugger code. If unset, uses
220 BEGIN { require 'perl5db.pl' }
224 A colon-separated list of directories in which to look for Perl library
225 files before looking in the standard library and the current
226 directory. If PERL5LIB is defined, PERLLIB is not used.
230 Apart from these, Perl uses no other environment variables, except
231 to make them available to the script being executed, and to child
232 processes. However, scripts running setuid would do well to execute
233 the following lines before doing anything else, just to keep people
236 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
237 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
238 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
242 Larry Wall E<lt><F<lwall@netlabs.com>E<gt>, with the help of oodles of other folks.
246 "/tmp/perl-e$$" temporary file for -e commands
247 "@INC" locations of perl 5 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 coredump 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 identifier 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 See the perl bugs database at F<http://perl.com/perl/bugs/>. You may
291 mail your bug reports (be sure to include full configuration information
292 as output by the myconfig program in the perl source tree) to
295 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
296 don't tell anyone I said that.
300 The Perl motto is "There's more than one way to do it." Divining
301 how many more is left as an exercise to the reader.
303 The three principal virtues of a programmer are Laziness,
304 Impatience, and Hubris. See the Camel Book for why.