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
35 perlref Perl references
36 perldsc Perl data structures intro
37 perllol Perl data structures: lists of lists
39 perltie Perl objects hidden behind simple variables
40 perlbot Perl OO tricks and examples
41 perlipc Perl interprocess communication
43 perldebug Perl debugging
44 perldiag Perl diagnostic messages
46 perltrap Perl traps for the unwary
47 perlstyle Perl style guide
49 perlpod Perl plain old documentation
50 perlbook Perl book information
52 perlembed Perl how to embed perl in your C or C++ app
53 perlapio Perl internal IO abstraction interface
54 perlxs Perl XS application programming interface
55 perlxstut Perl XS tutorial
56 perlguts Perl internal functions for those doing extensions
57 perlcall Perl calling conventions from C
59 (If you're intending to read these straight through for the first time,
60 the suggested order will tend to reduce the number of forward references.)
62 Additional documentation for Perl modules is available in the
63 F</usr/local/man/> directory. Some of this is distributed standard with
64 Perl, but you'll also find third-party modules there. You should be able
65 to view this with your man(1) program by including the proper directories
66 in the appropriate start-up files. To find out where these are, type:
70 If the directories were F</usr/local/man/man1> and F</usr/local/man/man3>,
71 you would only need to add F</usr/local/man> to your MANPATH. If
72 they are different, you'll have to add both stems.
74 If that doesn't work for some reason, you can still use the
75 supplied F<perldoc> script to view module information. You might
76 also look into getting a replacement man program.
78 If something strange has gone wrong with your program and you're not
79 sure where you should look for help, try the B<-w> switch first. It
80 will often point out exactly where the trouble is.
84 Perl is an interpreted language optimized for scanning arbitrary
85 text files, extracting information from those text files, and printing
86 reports based on that information. It's also a good language for many
87 system management tasks. The language is intended to be practical
88 (easy to use, efficient, complete) rather than beautiful (tiny,
91 Perl combines (in the author's opinion, anyway) some
92 of the best features of C, B<sed>, B<awk>, and B<sh>, so people
93 familiar with those languages should have little difficulty with it.
94 (Language historians will also note some vestiges of B<csh>, Pascal,
95 and even BASIC-PLUS.) Expression syntax corresponds quite closely to C
96 expression syntax. Unlike most Unix utilities, Perl does not
97 arbitrarily limit the size of your data--if you've got the memory,
98 Perl can slurp in your whole file as a single string. Recursion is
99 of unlimited depth. And the hash tables used by associative arrays
100 grow as necessary to prevent degraded performance. Perl uses
101 sophisticated pattern matching techniques to scan large amounts of data
102 very quickly. Although optimized for scanning text, Perl can also
103 deal with binary data, and can make dbm files look like associative
104 arrays. Setuid Perl scripts are safer than
105 C programs through a dataflow tracing mechanism which prevents many
106 stupid security holes. If you have a problem that would ordinarily use
107 B<sed> or B<awk> or B<sh>, but it exceeds their capabilities or must
108 run a little faster, and you don't want to write the silly thing in C,
109 then Perl may be for you. There are also translators to turn your
110 B<sed> and B<awk> scripts into Perl scripts.
112 But wait, there's more...
114 Perl version 5 is nearly a complete rewrite, and provides
115 the following additional benefits:
119 =item * Many usability enhancements
121 It is now possible to write much more readable Perl code (even within
122 regular expressions). Formerly cryptic variable names can be replaced
123 by mnemonic identifiers. Error messages are more informative, and the
124 optional warnings will catch many of the mistakes a novice might make.
125 This cannot be stressed enough. Whenever you get mysterious behavior,
126 try the B<-w> switch!!! Whenever you don't get mysterious behavior,
127 try using B<-w> anyway.
129 =item * Simplified grammar
131 The new yacc grammar is one half the size of the old one. Many of the
132 arbitrary grammar rules have been regularized. The number of reserved
133 words has been cut by 2/3. Despite this, nearly all old Perl scripts
134 will continue to work unchanged.
136 =item * Lexical scoping
138 Perl variables may now be declared within a lexical scope, like "auto"
139 variables in C. Not only is this more efficient, but it contributes
140 to better privacy for "programming in the large".
142 =item * Arbitrarily nested data structures
144 Any scalar value, including any array element, may now contain a
145 reference to any other variable or subroutine. You can easily create
146 anonymous variables and subroutines. Perl manages your reference
149 =item * Modularity and reusability
151 The Perl library is now defined in terms of modules which can be easily
152 shared among various packages. A package may choose to import all or a
153 portion of a module's published interface. Pragmas (that is, compiler
154 directives) are defined and used by the same mechanism.
156 =item * Object-oriented programming
158 A package can function as a class. Dynamic multiple inheritance and
159 virtual methods are supported in a straightforward manner and with very
160 little new syntax. Filehandles may now be treated as objects.
162 =item * Embeddable and Extensible
164 Perl may now be embedded easily in your C or C++ application, and can
165 either call or be called by your routines through a documented
166 interface. The XS preprocessor is provided to make it easy to glue
167 your C or C++ routines into Perl. Dynamic loading of modules is
170 =item * POSIX compliant
172 A major new module is the POSIX module, which provides access to all
173 available POSIX routines and definitions, via object classes where
176 =item * Package constructors and destructors
178 The new BEGIN and END blocks provide means to capture control as
179 a package is being compiled, and after the program exits. As a
180 degenerate case they work just like awk's BEGIN and END when you
181 use the B<-p> or B<-n> switches.
183 =item * Multiple simultaneous DBM implementations
185 A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB
186 files from the same script simultaneously. In fact, the old dbmopen
187 interface has been generalized to allow any variable to be tied
188 to an object class which defines its access methods.
190 =item * Subroutine definitions may now be autoloaded
192 In fact, the AUTOLOAD mechanism also allows you to define any arbitrary
193 semantics for undefined subroutine calls. It's not just for autoloading.
195 =item * Regular expression enhancements
197 You can now specify non-greedy quantifiers. You can now do grouping
198 without creating a backreference. You can now write regular expressions
199 with embedded whitespace and comments for readability. A consistent
200 extensibility mechanism has been added that is upwardly compatible with
201 all old regular expressions.
205 Ok, that's I<definitely> enough hype.
213 Used if chdir has no argument.
217 Used if chdir has no argument and HOME is not set.
221 Used in executing subprocesses, and in finding the script if B<-S> is
226 A colon-separated list of directories in which to look for Perl library
227 files before looking in the standard library and the current
228 directory. If PERL5LIB is not defined, PERLLIB is used. When running
229 taint checks (because the script was running setuid or setgid, or the
230 B<-T> switch was used), neither variable is used. The script should
233 use lib "/my/directory";
237 The command used to get the debugger code. If unset, uses
239 BEGIN { require 'perl5db.pl' }
243 A colon-separated list of directories in which to look for Perl library
244 files before looking in the standard library and the current
245 directory. If PERL5LIB is defined, PERLLIB is not used.
249 Apart from these, Perl uses no other environment variables, except
250 to make them available to the script being executed, and to child
251 processes. However, scripts running setuid would do well to execute
252 the following lines before doing anything else, just to keep people
255 $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
256 $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
257 $ENV{'IFS'} = '' if defined $ENV{'IFS'};
261 Larry Wall E<lt>F<lwall@sems.com>E<gt>, with the help of oodles of other folks.
265 "/tmp/perl-e$$" temporary file for -e commands
266 "@INC" locations of perl 5 libraries
270 a2p awk to perl translator
272 s2p sed to perl translator
276 The B<-w> switch produces some lovely diagnostics.
278 See L<perldiag> for explanations of all Perl's diagnostics.
280 Compilation errors will tell you the line number of the error, with an
281 indication of the next token or token type that was to be examined.
282 (In the case of a script passed to Perl via B<-e> switches, each
283 B<-e> is counted as one line.)
285 Setuid scripts have additional constraints that can produce error
286 messages such as "Insecure dependency". See L<perlsec>.
288 Did we mention that you should definitely consider using the B<-w>
293 The B<-w> switch is not mandatory.
295 Perl is at the mercy of your machine's definitions of various
296 operations such as type casting, atof() and sprintf(). The latter
297 can even trigger a coredump when passed ludicrous input values.
299 If your stdio requires a seek or eof between reads and writes on a
300 particular stream, so does Perl. (This doesn't apply to sysread()
303 While none of the built-in data types have any arbitrary size limits
304 (apart from memory size), there are still a few arbitrary limits: a
305 given variable name may not be longer than 255 characters, and no
306 component of your PATH may be longer than 255 if you use B<-S>. A regular
307 expression may not compile to more than 32767 bytes internally.
309 See the perl bugs database at F< http://perl.com/perl/bugs/ >. You may
310 mail your bug reports (be sure to include full configuration information
311 as output by the myconfig program in the perl source tree) to
313 If you've succeeded in compiling perl, the perlbug script in the utils/
314 subdirectory can be used to help mail in a bug report.
316 Perl actually stands for Pathologically Eclectic Rubbish Lister, but
317 don't tell anyone I said that.
321 The Perl motto is "There's more than one way to do it." Divining
322 how many more is left as an exercise to the reader.
324 The three principal virtues of a programmer are Laziness,
325 Impatience, and Hubris. See the Camel Book for why.