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 perlnews Perl news about changes from 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
94 of the best features of C, B<sed>, B<awk>, and B<sh>, so people
95 familiar with those languages should have little difficulty with it.
96 (Language historians will also note some vestiges of B<csh>, Pascal,
97 and even 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
101 of unlimited depth. And the hash tables used by associative arrays
102 grow as necessary to prevent degraded performance. Perl uses
103 sophisticated pattern matching techniques to scan large amounts of data
104 very quickly. Although optimized for scanning text, Perl can also
105 deal with binary data, and can make dbm files look like associative
106 arrays. Setuid Perl scripts are safer than
107 C programs through a dataflow tracing mechanism which prevents many
108 stupid security holes. If you have a problem that would ordinarily use
109 B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
110 run a little faster, and you don't want to write the silly thing in C,
111 then Perl may be for you. There are also translators to turn your
112 B<sed> and B<awk> scripts into Perl scripts.
114 But wait, there's more...
116 Perl version 5 is nearly a complete rewrite, and provides
117 the following additional benefits:
121 =item * Many usability enhancements
123 It is now possible to write much more readable Perl code (even within
124 regular expressions). Formerly cryptic variable names can be replaced
125 by mnemonic identifiers. Error messages are more informative, and the
126 optional warnings will catch many of the mistakes a novice might make.
127 This cannot be stressed enough. Whenever you get mysterious behavior,
128 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
129 try using B<-w> anyway.
131 =item * Simplified grammar
133 The new yacc grammar is one half the size of the old one. Many of the
134 arbitrary grammar rules have been regularized. The number of reserved
135 words has been cut by 2/3. Despite this, nearly all old Perl scripts
136 will continue to work unchanged.
138 =item * Lexical scoping
140 Perl variables may now be declared within a lexical scope, like "auto"
141 variables in C. Not only is this more efficient, but it contributes
142 to better privacy for "programming in the large". Anonymous
143 subroutines exhibit deep binding of lexical variables (closures).
145 =item * Arbitrarily nested data structures
147 Any scalar value, including any array element, may now contain a
148 reference to any other variable or subroutine. You can easily create
149 anonymous variables and subroutines. Perl manages your reference
152 =item * Modularity and reusability
154 The Perl library is now defined in terms of modules which can be easily
155 shared among various packages. A package may choose to import all or a
156 portion of a module's published interface. Pragmas (that is, compiler
157 directives) are defined and used by the same mechanism.
159 =item * Object-oriented programming
161 A package can function as a class. Dynamic multiple inheritance and
162 virtual methods are supported in a straightforward manner and with very
163 little new syntax. Filehandles may now be treated as objects.
165 =item * Embeddable and Extensible
167 Perl may now be embedded easily in your C or C++ application, and can
168 either call or be called by your routines through a documented
169 interface. The XS preprocessor is provided to make it easy to glue
170 your C or C++ routines into Perl. Dynamic loading of modules is
171 supported, and Perl itself can be made into a dynamic library.
173 =item * POSIX compliant
175 A major new module is the POSIX module, which provides access to all
176 available POSIX routines and definitions, via object classes where
179 =item * Package constructors and destructors
181 The new BEGIN and END blocks provide means to capture control as
182 a package is being compiled, and after the program exits. As a
183 degenerate case they work just like awk's BEGIN and END when you
184 use the B<-p> or B<-n> switches.
186 =item * Multiple simultaneous DBM implementations
188 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
189 files from the same script simultaneously. In fact, the old dbmopen
190 interface has been generalized to allow any variable to be tied
191 to an object class which defines its access methods.
193 =item * Subroutine definitions may now be autoloaded
195 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
196 semantics for undefined subroutine calls. It's not for just autoloading.
198 =item * Regular expression enhancements
200 You can now specify non-greedy quantifiers. You can now do grouping
201 without creating a backreference. You can now write regular expressions
202 with embedded whitespace and comments for readability. A consistent
203 extensibility mechanism has been added that is upwardly compatible with
204 all old regular expressions.
206 =item * Innumerable Unbundled Modules
208 The Comprehensive Perl Archive Network described in L<perlmod>
209 contains hundreds of plug-and-play modules full of reusable
210 code. See F<http://www.perl.com/CPAN> for a site near you.
212 =item * Compilability
214 While not yet in full production mode, a working perl-to-C compiler
215 does exist. It can generate portable bytecode, simple C, or
220 Ok, that's I<definitely> enough hype.
228 Used if chdir has no argument.
232 Used if chdir has no argument and HOME is not set.
236 Used in executing subprocesses, and in finding the script if B<-S> is
241 A colon-separated list of directories in which to look for Perl library
242 files before looking in the standard library and the current
243 directory. If PERL5LIB is not defined, PERLLIB is used. When running
244 taint checks (because the script was running setuid or setgid, or the
245 B<-T> switch was used), neither variable is used. The script should
248 use lib "/my/directory";
252 The command used to get the debugger code. If unset, uses
254 BEGIN { require 'perl5db.pl' }
256 =item PERL_DESTRUCT_LEVEL
258 Relevant only if your perl executable was built with B<-DDEBUGGING>,
259 this controls the behavior of global destruction of objects and other
264 A colon-separated list of directories in which to look for Perl library
265 files before looking in the standard library and the current
266 directory. If PERL5LIB is defined, PERLLIB is not used.
270 Perl also has environment variables that control how Perl handles
271 language-specific data. Please consult the L<perli18n> section.
273 Apart from these, Perl uses no other environment variables, except
274 to make them available to the script being executed, and to child
275 processes. However, scripts running setuid would do well to execute
276 the following lines before doing anything else, just to keep people
279 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
280 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
281 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
285 Larry Wall E<lt>F<larry@wall.org>E<gt>, with the help of oodles of other folks.
289 "/tmp/perl-e$$" temporary file for -e commands
290 "@INC" locations of perl libraries
294 a2p awk to perl translator
296 s2p sed to perl translator
300 The B<-w> switch produces some lovely diagnostics.
302 See L<perldiag> for explanations of all Perl's diagnostics.
304 Compilation errors will tell you the line number of the error, with an
305 indication of the next token or token type that was to be examined.
306 (In the case of a script passed to Perl via B<-e> switches, each
307 B<-e> is counted as one line.)
309 Setuid scripts have additional constraints that can produce error
310 messages such as "Insecure dependency". See L<perlsec>.
312 Did we mention that you should definitely consider using the B<-w>
317 The B<-w> switch is not mandatory.
319 Perl is at the mercy of your machine's definitions of various
320 operations such as type casting, atof(), and sprintf(). The latter
321 can even trigger a core dump when passed ludicrous input values.
323 If your stdio requires a seek or eof between reads and writes on a
324 particular stream, so does Perl. (This doesn't apply to sysread()
327 While none of the built-in data types have any arbitrary size limits
328 (apart from memory size), there are still a few arbitrary limits: a
329 given variable name may not be longer than 255 characters, and no
330 component of your PATH may be longer than 255 if you use B<-S>. A regular
331 expression may not compile to more than 32767 bytes internally.
333 See the perl bugs database at F<http://www.perl.com/perl/bugs/>. You may
334 mail your bug reports (be sure to include full configuration information
335 as output by the myconfig program in the perl source tree, or by C<perl -V>) to
337 If you've succeeded in compiling perl, the perlbug script in the utils/
338 subdirectory can be used to help mail in a bug report.
340 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
341 don't tell anyone I said that.
345 The Perl motto is "There's more than one way to do it." Divining
346 how many more is left as an exercise to the reader.
348 The three principal virtues of a programmer are Laziness,
349 Impatience, and Hubris. See the Camel Book for why.