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 perltoc Perl documentation table of contents
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 perli18n Perl internalization
36 perlref Perl references
37 perldsc Perl data structures intro
38 perllol Perl data structures: lists of lists
40 perltie Perl objects hidden behind simple variables
41 perlbot Perl OO tricks and examples
42 perlipc Perl interprocess communication
44 perldebug Perl debugging
45 perldiag Perl diagnostic messages
47 perltrap Perl traps for the unwary
48 perlstyle Perl style guide
50 perlpod Perl plain old documentation
51 perlbook Perl book information
53 perlembed Perl how to embed perl in your C or C++ app
54 perlapio Perl internal IO abstraction interface
55 perlxs Perl XS application programming interface
56 perlxstut Perl XS tutorial
57 perlguts Perl internal functions for those doing extensions
58 perlcall Perl calling conventions from C
60 (If you're intending to read these straight through for the first time,
61 the suggested order will tend to reduce the number of forward references.)
63 Additional documentation for Perl modules is available in the
64 F</usr/local/man/> directory. Some of this is distributed standard with
65 Perl, but you'll also find third-party modules there. You should be able
66 to view this with your man(1) program by including the proper directories
67 in the appropriate start-up files. To find out where these are, type:
71 If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
72 you would only need to add F</usr/local/man> to your MANPATH. If
73 they are different, you'll have to add both stems.
75 If that doesn't work for some reason, you can still use the
76 supplied F<perldoc> script to view module information. You might
77 also look into getting a replacement man program.
79 If something strange has gone wrong with your program and you're not
80 sure where you should look for help, try the B<-w> switch first. It
81 will often point out exactly where the trouble is.
85 Perl is an interpreted language optimized for scanning arbitrary
86 text files, extracting information from those text files, and printing
87 reports based on that information. It's also a good language for many
88 system management tasks. The language is intended to be practical
89 (easy to use, efficient, complete) rather than beautiful (tiny,
92 Perl combines (in the author's opinion, anyway) some
93 of the best features of C, B<sed>, B<awk>, and B<sh>, so people
94 familiar with those languages should have little difficulty with it.
95 (Language historians will also note some vestiges of B<csh>, Pascal,
96 and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
97 expression syntax. Unlike most Unix utilities, Perl does not
98 arbitrarily limit the size of your data--if you've got the memory,
99 Perl can slurp in your whole file as a single string. Recursion is
100 of unlimited depth. And the hash tables used by associative arrays
101 grow as necessary to prevent degraded performance. Perl uses
102 sophisticated pattern matching techniques to scan large amounts of data
103 very quickly. Although optimized for scanning text, Perl can also
104 deal with binary data, and can make dbm files look like associative
105 arrays. Setuid Perl scripts are safer than
106 C programs through a dataflow tracing mechanism which prevents many
107 stupid security holes. If you have a problem that would ordinarily use
108 B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
109 run a little faster, and you don't want to write the silly thing in C,
110 then Perl may be for you. There are also translators to turn your
111 B<sed> and B<awk> scripts into Perl scripts.
113 But wait, there's more...
115 Perl version 5 is nearly a complete rewrite, and provides
116 the following additional benefits:
120 =item * Many usability enhancements
122 It is now possible to write much more readable Perl code (even within
123 regular expressions). Formerly cryptic variable names can be replaced
124 by mnemonic identifiers. Error messages are more informative, and the
125 optional warnings will catch many of the mistakes a novice might make.
126 This cannot be stressed enough. Whenever you get mysterious behavior,
127 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
128 try using B<-w> anyway.
130 =item * Simplified grammar
132 The new yacc grammar is one half the size of the old one. Many of the
133 arbitrary grammar rules have been regularized. The number of reserved
134 words has been cut by 2/3. Despite this, nearly all old Perl scripts
135 will continue to work unchanged.
137 =item * Lexical scoping
139 Perl variables may now be declared within a lexical scope, like "auto"
140 variables in C. Not only is this more efficient, but it contributes
141 to better privacy for "programming in the large".
143 =item * Arbitrarily nested data structures
145 Any scalar value, including any array element, may now contain a
146 reference to any other variable or subroutine. You can easily create
147 anonymous variables and subroutines. Perl manages your reference
150 =item * Modularity and reusability
152 The Perl library is now defined in terms of modules which can be easily
153 shared among various packages. A package may choose to import all or a
154 portion of a module's published interface. Pragmas (that is, compiler
155 directives) are defined and used by the same mechanism.
157 =item * Object-oriented programming
159 A package can function as a class. Dynamic multiple inheritance and
160 virtual methods are supported in a straightforward manner and with very
161 little new syntax. Filehandles may now be treated as objects.
163 =item * Embeddable and Extensible
165 Perl may now be embedded easily in your C or C++ application, and can
166 either call or be called by your routines through a documented
167 interface. The XS preprocessor is provided to make it easy to glue
168 your C or C++ routines into Perl. Dynamic loading of modules is
171 =item * POSIX compliant
173 A major new module is the POSIX module, which provides access to all
174 available POSIX routines and definitions, via object classes where
177 =item * Package constructors and destructors
179 The new BEGIN and END blocks provide means to capture control as
180 a package is being compiled, and after the program exits. As a
181 degenerate case they work just like awk's BEGIN and END when you
182 use the B<-p> or B<-n> switches.
184 =item * Multiple simultaneous DBM implementations
186 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
187 files from the same script simultaneously. In fact, the old dbmopen
188 interface has been generalized to allow any variable to be tied
189 to an object class which defines its access methods.
191 =item * Subroutine definitions may now be autoloaded
193 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
194 semantics for undefined subroutine calls. It's not just for autoloading.
196 =item * Regular expression enhancements
198 You can now specify non-greedy quantifiers. You can now do grouping
199 without creating a backreference. You can now write regular expressions
200 with embedded whitespace and comments for readability. A consistent
201 extensibility mechanism has been added that is upwardly compatible with
202 all old regular expressions.
206 Ok, that's I<definitely> enough hype.
214 Used if chdir has no argument.
218 Used if chdir has no argument and HOME is not set.
222 Used in executing subprocesses, and in finding the script if B<-S> is
227 A colon-separated list of directories in which to look for Perl library
228 files before looking in the standard library and the current
229 directory. If PERL5LIB is not defined, PERLLIB is used. When running
230 taint checks (because the script was running setuid or setgid, or the
231 B<-T> switch was used), neither variable is used. The script should
234 use lib "/my/directory";
238 The command used to get the debugger code. If unset, uses
240 BEGIN { require 'perl5db.pl' }
244 A colon-separated list of directories in which to look for Perl library
245 files before looking in the standard library and the current
246 directory. If PERL5LIB is defined, PERLLIB is not used.
250 Perl also has environment variables that control how Perl handles
251 language-specific data. Please consult the L<perli18n> section.
253 Apart from these, Perl uses no other environment variables, except
254 to make them available to the script being executed, and to child
255 processes. However, scripts running setuid would do well to execute
256 the following lines before doing anything else, just to keep people
259 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
260 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
261 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
265 Larry Wall E<lt>F<larry@wall.org>E<gt>, with the help of oodles of other folks.
269 "/tmp/perl-e$$" temporary file for -e commands
270 "@INC" locations of perl 5 libraries
274 a2p awk to perl translator
276 s2p sed to perl translator
280 The B<-w> switch produces some lovely diagnostics.
282 See L<perldiag> for explanations of all Perl's diagnostics.
284 Compilation errors will tell you the line number of the error, with an
285 indication of the next token or token type that was to be examined.
286 (In the case of a script passed to Perl via B<-e> switches, each
287 B<-e> is counted as one line.)
289 Setuid scripts have additional constraints that can produce error
290 messages such as "Insecure dependency". See L<perlsec>.
292 Did we mention that you should definitely consider using the B<-w>
297 The B<-w> switch is not mandatory.
299 Perl is at the mercy of your machine's definitions of various
300 operations such as type casting, atof() and sprintf(). The latter
301 can even trigger a coredump when passed ludicrous input values.
303 If your stdio requires a seek or eof between reads and writes on a
304 particular stream, so does Perl. (This doesn't apply to sysread()
307 While none of the built-in data types have any arbitrary size limits
308 (apart from memory size), there are still a few arbitrary limits: a
309 given variable name may not be longer than 255 characters, and no
310 component of your PATH may be longer than 255 if you use B<-S>. A regular
311 expression may not compile to more than 32767 bytes internally.
313 See the perl bugs database at F<http://perl.com/perl/bugs/>. You may
314 mail your bug reports (be sure to include full configuration information
315 as output by the myconfig program in the perl source tree, or by C<perl -V>) to
317 If you've succeeded in compiling perl, the perlbug script in the utils/
318 subdirectory can be used to help mail in a bug report.
320 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
321 don't tell anyone I said that.
325 The Perl motto is "There's more than one way to do it." Divining
326 how many more is left as an exercise to the reader.
328 The three principal virtues of a programmer are Laziness,
329 Impatience, and Hubris. See the Camel Book for why.