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 perldata Perl data structures
13 perlop Perl operators and precedence
14 perlre Perl regular expressions
15 perlrun Perl execution and options
16 perlfunc Perl builtin functions
17 perlvar Perl predefined variables
18 perlsub Perl subroutines
20 perlref Perl references and nested data structures
22 perlbot Perl OO tricks and examples
23 perldebug Perl debugging
24 perldiag Perl diagnostic messages
26 perlipc Perl interprocess communication
28 perltrap Perl traps for the unwary
29 perlstyle Perl style guide
30 perlapi Perl application programming interface
31 perlguts Perl internal functions for those doing extensions
32 perlcall Perl calling conventions from C
33 perlovl Perl overloading semantics
34 perlbook Perl book information
36 (If you're intending to read these straight through for the first time,
37 the suggested order will tend to reduce the number of forward references.)
39 Additional documentation for perl modules is available in
40 the F</usr/local/lib/perl5/man/man3> directory. You can view this
41 with a man(1) program by including the following in the
42 appropriate start-up files. (You may have to adjust the path to
43 match $Config{'man3dir'}.)
45 .profile (for sh, bash or ksh users):
46 MANPATH=$MANPATH:/usr/local/lib/perl5/man
49 .login (for csh or tcsh users):
50 setenv MANPATH $MANPATH:/usr/local/lib/perl5/man
52 If that doesn't work for some reason, you can still use the
53 supplied perldoc script to view module information.
55 If something strange has gone wrong with your program and you're not
56 sure where you should look for help, try the B<-w> switch first. It
57 will often point out exactly where the trouble is.
61 Perl is an interpreted language optimized for scanning arbitrary
62 text files, extracting information from those text files, and printing
63 reports based on that information. It's also a good language for many
64 system management tasks. The language is intended to be practical
65 (easy to use, efficient, complete) rather than beautiful (tiny,
66 elegant, minimal). It combines (in the author's opinion, anyway) some
67 of the best features of C, B<sed>, B<awk>, and B<sh>, so people
68 familiar with those languages should have little difficulty with it.
69 (Language historians will also note some vestiges of B<csh>, Pascal,
70 and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
71 expression syntax. Unlike most Unix utilities, Perl does not
72 arbitrarily limit the size of your data--if you've got the memory,
73 Perl can slurp in your whole file as a single string. Recursion is
74 of unlimited depth. And the hash tables used by associative arrays
75 grow as necessary to prevent degraded performance. Perl uses
76 sophisticated pattern matching techniques to scan large amounts of data
77 very quickly. Although optimized for scanning text, Perl can also
78 deal with binary data, and can make dbm files look like associative
79 arrays (where dbm is available). Setuid Perl scripts are safer than
80 C programs through a dataflow tracing mechanism which prevents many
81 stupid security holes. If you have a problem that would ordinarily use
82 B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
83 run a little faster, and you don't want to write the silly thing in C,
84 then Perl may be for you. There are also translators to turn your
85 B<sed> and B<awk> scripts into Perl scripts.
87 But wait, there's more...
89 Perl version 5 is nearly a complete rewrite, and provides
90 the following additional benefits:
94 =item * Many usability enhancements
96 It is now possible to write much more readable Perl code (even within
97 regular expressions). Formerly cryptic variable names can be replaced
98 by mnemonic identifiers. Error messages are more informative, and the
99 optional warnings will catch many of the mistakes a novice might make.
100 This cannot be stressed enough. Whenever you get mysterious behavior,
101 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
102 try using B<-w> anyway.
104 =item * Simplified grammar
106 The new yacc grammar is one half the size of the old one. Many of the
107 arbitrary grammar rules have been regularized. The number of reserved
108 words has been cut by 2/3. Despite this, nearly all old Perl scripts
109 will continue to work unchanged.
111 =item * Lexical scoping
113 Perl variables may now be declared within a lexical scope, like "auto"
114 variables in C. Not only is this more efficient, but it contributes
115 to better privacy for "programming in the large".
117 =item * Arbitrarily nested data structures
119 Any scalar value, including any array element, may now contain a
120 reference to any other variable or subroutine. You can easily create
121 anonymous variables and subroutines. Perl manages your reference
124 =item * Modularity and reusability
126 The Perl library is now defined in terms of modules which can be easily
127 shared among various packages. A package may choose to import all or a
128 portion of a module's published interface. Pragmas (that is, compiler
129 directives) are defined and used by the same mechanism.
131 =item * Object-oriented programming
133 A package can function as a class. Dynamic multiple inheritance and
134 virtual methods are supported in a straightforward manner and with very
135 little new syntax. Filehandles may now be treated as objects.
137 =item * Embeddible and Extensible
139 Perl may now be embedded easily in your C or C++ application, and can
140 either call or be called by your routines through a documented
141 interface. The XS preprocessor is provided to make it easy to glue
142 your C or C++ routines into Perl. Dynamic loading of modules is
145 =item * POSIX compliant
147 A major new module is the POSIX module, which provides access to all
148 available POSIX routines and definitions, via object classes where
151 =item * Package constructors and destructors
153 The new BEGIN and END blocks provide means to capture control as
154 a package is being compiled, and after the program exits. As a
155 degenerate case they work just like awk's BEGIN and END when you
156 use the B<-p> or B<-n> switches.
158 =item * Multiple simultaneous DBM implementations
160 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
161 files from the same script simultaneously. In fact, the old dbmopen
162 interface has been generalized to allow any variable to be tied
163 to an object class which defines its access methods.
165 =item * Subroutine definitions may now be autoloaded
167 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
168 semantics for undefined subroutine calls. It's not just for autoloading.
170 =item * Regular expression enhancements
172 You can now specify non-greedy quantifiers. You can now do grouping
173 without creating a backreference. You can now write regular expressions
174 with embedded whitespace and comments for readability. A consistent
175 extensibility mechanism has been added that is upwardly compatible with
176 all old regular expressions.
180 Ok, that's I<definitely> enough hype.
188 Used if chdir has no argument.
192 Used if chdir has no argument and HOME is not set.
196 Used in executing subprocesses, and in finding the script if B<-S> is
201 A colon-separated list of directories in which to look for Perl library
202 files before looking in the standard library and the current
203 directory. If PERL5LIB is not defined, PERLLIB is used.
207 The command used to get the debugger code. If unset, uses
209 BEGIN { require 'perl5db.pl' }
213 A colon-separated list of directories in which to look for Perl library
214 files before looking in the standard library and the current
215 directory. If PERL5LIB is defined, PERLLIB is not used.
220 Apart from these, Perl uses no other environment variables, except
221 to make them available to the script being executed, and to child
222 processes. However, scripts running setuid would do well to execute
223 the following lines before doing anything else, just to keep people
226 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
227 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
228 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
232 Larry Wall <F<lwall@netlabs.com.>, with the help of oodles of other folks.
236 "/tmp/perl-e$$" temporary file for -e commands
237 "@INC" locations of perl 5 libraries
241 a2p awk to perl translator
242 s2p sed to perl translator
246 The B<-w> switch produces some lovely diagnostics.
248 See L<perldiag> for explanations of all Perl's diagnostics.
250 Compilation errors will tell you the line number of the error, with an
251 indication of the next token or token type that was to be examined.
252 (In the case of a script passed to Perl via B<-e> switches, each
253 B<-e> is counted as one line.)
255 Setuid scripts have additional constraints that can produce error
256 messages such as "Insecure dependency". See L<perlsec>.
258 Did we mention that you should definitely consider using the B<-w>
263 The B<-w> switch is not mandatory.
265 Perl is at the mercy of your machine's definitions of various
266 operations such as type casting, atof() and sprintf().
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 identifier 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 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
279 don't tell anyone I said that.
283 The Perl motto is "There's more than one way to do it." Divining
284 how many more is left as an exercise to the reader.
286 The three principle virtues of a programmer are Laziness,
287 Impatience, and Hubris. See the Camel Book for why.