perl - Practical Extraction and Report Language
perl [ -sTuU ] [ -hv ] [ -V[:configvar] ] [ -cw ] [ -d[:debugger] ] [ -D[number/list] ] [ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal] ] [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -P ] [ -S ] [ -x[dir] ] [ -i[extension] ] [ -e 'command' ] [ -- ] [ programfile ] [ argument ]...
For ease of access, the Perl manual has been split up into several sections:
perl Perl overview (this section) perldelta Perl changes since previous version perl5005delta Perl changes in version 5.005 perl5004delta Perl changes in version 5.004 perlfaq Perl frequently asked questions perltoc Perl documentation table of contents perldata Perl data structures perlsyn Perl syntax perlop Perl operators and precedence perlre Perl regular expressions perlrun Perl execution and options perlfunc Perl builtin functions perlopentut Perl open() tutorial perlvar Perl predefined variables perlsub Perl subroutines perlmod Perl modules: how they work perlmodlib Perl modules: how to write and use perlmodinstall Perl modules: how to install from CPAN perlform Perl formats perlunicode Perl unicode support perllocale Perl locale support perlreftut Perl references short introduction perlref Perl references, the rest of the story perldsc Perl data structures intro perllol Perl data structures: arrays of arrays perlboot Perl OO tutorial for beginners perltoot Perl OO tutorial, part 1 perltootc Perl OO tutorial, part 2 perlobj Perl objects perltie Perl objects hidden behind simple variables perlbot Perl OO tricks and examples perlipc Perl interprocess communication perlfork Perl fork() information perlthrtut Perl threads tutorial perllexwarn Perl warnings and their control perlfilter Perl source filters perldbmfilter Perl DBM filters perlcompile Perl compiler suite intro perldebug Perl debugging perldiag Perl diagnostic messages perlnumber Perl number semantics perlsec Perl security perltrap Perl traps for the unwary perlport Perl portability guide perlstyle Perl style guide perlpod Perl plain old documentation perlbook Perl book information perlembed Perl ways to embed perl in your C or C++ application perlapio Perl internal IO abstraction interface perldebguts Perl debugging guts and tips perlxs Perl XS application programming interface perlxstut Perl XS tutorial perlguts Perl internal functions for those doing extensions perlcall Perl calling conventions from C perlapi Perl API listing (autogenerated) perlintern Perl internal functions (autogenerated) perltodo Perl things to do perlhack Perl hackers guide perlhist Perl history records perlamiga Perl notes for Amiga perlcygwin Perl notes for Cygwin perldos Perl notes for DOS perlhpux Perl notes for HP-UX perlmachten Perl notes for Power MachTen perlos2 Perl notes for OS/2 perlos390 Perl notes for OS/390 perlvms Perl notes for VMS perlwin32 Perl notes for Windows
(If you're intending to read these straight through for the first time, the suggested order will tend to reduce the number of forward references.)
By default, the manpages listed above are installed in the /usr/local/man/ directory.
Extensive additional documentation for Perl modules is available. The default configuration for perl will place this additional documentation in the /usr/local/lib/perl5/man directory (or else in the man subdirectory of the Perl library directory). Some of this additional documentation is distributed standard with Perl, but you'll also find documentation for third-party modules there.
You should be able to view Perl's documentation with your man(1) program by including the proper directories in the appropriate start-up files, or in the MANPATH environment variable. To find out where the configuration has installed the manpages, type:
If the directories have a common stem, such as /usr/local/man/man1 and /usr/local/man/man3, you need only to add that stem (/usr/local/man) to your man(1) configuration files or your MANPATH environment variable. If they do not share a stem, you'll have to add both stems.
If that doesn't work for some reason, you can still use the supplied perldoc script to view module information. You might also look into getting a replacement man program.
If something strange has gone wrong with your program and you're not sure where you should look for help, try the -w switch first. It will often point out exactly where the trouble is.
Perl is a language optimized for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for many system management tasks. The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal).
Perl combines (in the author's opinion, anyway) some of the best features of C, sed, awk, and sh, so people familiar with those languages should have little difficulty with it. (Language historians will also note some vestiges of csh, Pascal, and even BASIC-PLUS.) Expression syntax corresponds closely to C expression syntax. Unlike most Unix utilities, Perl does not arbitrarily limit the size of your data--if you've got the memory, Perl can slurp in your whole file as a single string. Recursion is of unlimited depth. And the tables used by hashes (sometimes called "associative arrays") grow as necessary to prevent degraded performance. Perl can use sophisticated pattern matching techniques to scan large amounts of data quickly. Although optimized for scanning text, Perl can also deal with binary data, and can make dbm files look like hashes. Setuid Perl scripts are safer than C programs through a dataflow tracing mechanism that prevents many stupid security holes.
If you have a problem that would ordinarily use sed or awk or sh, but it exceeds their capabilities or must run a little faster, and you don't want to write the silly thing in C, then Perl may be for you. There are also translators to turn your sed and awk scripts into Perl scripts.
But wait, there's more...
Begun in 1993 (see perlhist), Perl version 5 is nearly a complete rewrite that provides the following additional benefits:
modularity and reusability using innumerable modules
embeddable and extensible
roll-your-own magic variables (including multiple simultaneous DBM implementations)
subroutines can now be overridden, autoloaded, and prototyped
Described in perlsub.
arbitrarily nested data structures and anonymous functions
compilability into C code or Perl bytecode
support for light-weight processes (threads)
support for internationalization, localization, and Unicode
Described in perlsub.
regular expression enhancements
enhanced debugger and interactive Perl environment, with integrated editor support
Described in perldebug.
POSIX 1003.1 compliant library
Described in POSIX.
Okay, that's definitely enough hype.
Perl is available for most operating systems, including virtually all Unix-like platforms. See "Supported Platforms" in perlport for a listing.
Larry Wall <firstname.lastname@example.org>, with the help of oodles of other folks.
If your Perl success stories and testimonials may be of help to others who wish to advocate the use of Perl in their applications, or if you wish to simply express your gratitude to Larry and the Perl developers, please write to email@example.com .
"@INC" locations of perl libraries
a2p awk to perl translator s2p sed to perl translator http://www.perl.com/ the Perl Home Page http://www.perl.com/CPAN the Comprehensive Perl Archive
use warnings pragma (and the -w switch) produces some lovely diagnostics.
See perldiag for explanations of all Perl's diagnostics. The
use diagnostics pragma automatically turns Perl's normally terse warnings and errors into these longer forms.
Compilation errors will tell you the line number of the error, with an indication of the next token or token type that was to be examined. (In a script passed to Perl via -e switches, each -e is counted as one line.)
Setuid scripts have additional constraints that can produce error messages such as "Insecure dependency". See perlsec.
Did we mention that you should definitely consider using the -w switch?
The -w switch is not mandatory.
Perl is at the mercy of your machine's definitions of various operations such as type casting, atof(), and floating-point output with sprintf().
If your stdio requires a seek or eof between reads and writes on a particular stream, so does Perl. (This doesn't apply to sysread() and syswrite().)
While none of the built-in data types have any arbitrary size limits (apart from memory size), there are still a few arbitrary limits: a given variable name may not be longer than 251 characters. Line numbers displayed by diagnostics are internally stored as short integers, so they are limited to a maximum of 65535 (higher numbers usually being affected by wraparound).
You may mail your bug reports (be sure to include full configuration information as output by the myconfig program in the perl source tree, or by
perl -V) to firstname.lastname@example.org . If you've succeeded in compiling perl, the perlbug script in the utils/ subdirectory can be used to help mail in a bug report.
Perl actually stands for Pathologically Eclectic Rubbish Lister, but don't tell anyone I said that.
The Perl motto is "There's more than one way to do it." Divining how many more is left as an exercise to the reader.
The three principal virtues of a programmer are Laziness, Impatience, and Hubris. See the Camel Book for why.