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diff --git a/pod/perl.pod b/pod/perl.pod new file mode 100644 index 0000000000..9306d5c9c7 --- /dev/null +++ b/pod/perl.pod @@ -0,0 +1,271 @@ +=head1 NAME + +perl - Practical Extraction and Report Language + +=head1 SYNOPSIS + +For ease of access, the Perl manual has been split up into a number +of sections: + + perl Perl overview (this section) + 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 + perlvar Perl predefined variables + perlsub Perl subroutines + perlmod Perl modules + perlref Perl references and nested data structures + perlobj Perl objects + perlbot Perl OO tricks and examples + perldebug Perl debugging + perldiag Perl diagnostic messages + perlform Perl formats + perlipc Perl interprocess communication + perlsec Perl security + perltrap Perl traps for the unwary + perlstyle Perl style guide + perlapi Perl application programming interface + perlguts Perl internal functions for those doing extensions + perlcall Perl calling conventions from C + perlovl Perl overloading semantics + perlbook Perl book information + +(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.) + +If something strange has gone wrong with your program and you're not +sure where you should look for help, try the B<-w> switch first. It +will often point out exactly where the trouble is. + +=head1 DESCRIPTION + +Perl is an interpreted 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). It combines (in the author's opinion, anyway) some +of the best features of C, B<sed>, B<awk>, and B<sh>, so people +familiar with those languages should have little difficulty with it. +(Language historians will also note some vestiges of B<csh>, Pascal, +and even BASIC-PLUS.) Expression syntax corresponds quite 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 hash tables used by associative arrays +grow as necessary to prevent degraded performance. Perl uses +sophisticated pattern matching techniques to scan large amounts of data +very quickly. Although optimized for scanning text, Perl can also +deal with binary data, and can make dbm files look like associative +arrays (where dbm is available). Setuid Perl scripts are safer than +C programs through a dataflow tracing mechanism which prevents many +stupid security holes. If you have a problem that would ordinarily use +B<sed> or B<awk> or B<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 +B<sed> and B<awk> scripts into Perl scripts. + +But wait, there's more... + +Perl version 5 is nearly a complete rewrite, and provides +the following additional benefits: + +=over 5 + +=item * Many usability enhancements + +It is now possible to write much more readable Perl code (even within +regular expressions). Formerly cryptic variable names can be replaced +by mnemonic identifiers. Error messages are more informative, and the +optional warnings will catch many of the mistakes a novice might make. +This cannot be stressed enough. Whenever you get mysterious behavior, +try the B<-w> switch!!! Whenever you don't get mysterious behavior, +try using B<-w> anyway. + +=item * Simplified grammar + +The new yacc grammar is one half the size of the old one. Many of the +arbitrary grammar rules have been regularized. The number of reserved +words has been cut by 2/3. Despite this, nearly all old Perl scripts +will continue to work unchanged. + +=item * Lexical scoping + +Perl variables may now be declared within a lexical scope, like "auto" +variables in C. Not only is this more efficient, but it contributes +to better privacy for "programming in the large". + +=item * Arbitrarily nested data structures + +Any scalar value, including any array element, may now contain a +reference to any other variable or subroutine. You can easily create +anonymous variables and subroutines. Perl manages your reference +counts for you. + +=item * Modularity and reusability + +The Perl library is now defined in terms of modules which can be easily +shared among various packages. A package may choose to import all or a +portion of a module's published interface. Pragmas (that is, compiler +directives) are defined and used by the same mechanism. + +=item * Object-oriented programming + +A package can function as a class. Dynamic multiple inheritance and +virtual methods are supported in a straightforward manner and with very +little new syntax. Filehandles may now be treated as objects. + +=item * Embeddible and Extensible + +Perl may now be embedded easily in your C or C++ application, and can +either call or be called by your routines through a documented +interface. The XS preprocessor is provided to make it easy to glue +your C or C++ routines into Perl. Dynamic loading of modules is +supported. + +=item * POSIX compliant + +A major new module is the POSIX module, which provides access to all +available POSIX routines and definitions, via object classes where +appropriate. + +=item * Package constructors and destructors + +The new BEGIN and END blocks provide means to capture control as +a package is being compiled, and after the program exits. As a +degenerate case they work just like awk's BEGIN and END when you +use the B<-p> or B<-n> switches. + +=item * Multiple simultaneous DBM implementations + +A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB +files from the same script simultaneously. In fact, the old dbmopen +interface has been generalized to allow any variable to be tied +to an object class which defines its access methods. + +=item * Subroutine definitions may now be autoloaded + +In fact, the AUTOLOAD mechanism also allows you to define any arbitrary +semantics for undefined subroutine calls. It's not just for autoloading. + +=item * Regular expression enhancements + +You can now specify non-greedy quantifiers. You can now do grouping +without creating a backreference. You can now write regular expressions +with embedded whitespace and comments for readability. A consistent +extensibility mechanism has been added that is upwardly compatible with +all old regular expressions. + +=back + +Ok, that's I<definitely> enough hype. + +=head1 ENVIRONMENT + +=over 12 + +=item HOME + +Used if chdir has no argument. + +=item LOGDIR + +Used if chdir has no argument and HOME is not set. + +=item PATH + +Used in executing subprocesses, and in finding the script if B<-S> is +used. + +=item PERL5LIB + +A colon-separated list of directories in which to look for Perl library +files before looking in the standard library and the current +directory. If PERL5LIB is not defined, PERLLIB is used. + +=item PERL5DB + +The command used to get the debugger code. If unset, uses + + BEGIN { require 'perl5db.pl' } + +=item PERLLIB + +A colon-separated list of directories in which to look for Perl library +files before looking in the standard library and the current +directory. If PERL5LIB is defined, PERLLIB is not used. + + +=back + +Apart from these, Perl uses no other environment variables, except +to make them available to the script being executed, and to child +processes. However, scripts running setuid would do well to execute +the following lines before doing anything else, just to keep people +honest: + + $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need + $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'}; + $ENV{'IFS'} = '' if defined $ENV{'IFS'}; + +=head1 AUTHOR + +Larry Wall <F<lwall@netlabs.com.>, with the help of oodles of other folks. + +=head1 FILES + + "/tmp/perl-e$$" temporary file for -e commands + "@INC" locations of perl 5 libraries + +=head1 SEE ALSO + + a2p awk to perl translator + s2p sed to perl translator + +=head1 DIAGNOSTICS + +The B<-w> switch produces some lovely diagnostics. + +See L<perldiag> for explanations of all Perl's diagnostics. + +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 the case of a script passed to Perl via B<-e> switches, each +B<-e> is counted as one line.) + +Setuid scripts have additional constraints that can produce error +messages such as "Insecure dependency". See L<perlsec>. + +Did we mention that you should definitely consider using the B<-w> +switch? + +=head1 BUGS + +The B<-w> switch is not mandatory. + +Perl is at the mercy of your machine's definitions of various +operations such as type casting, atof() and sprintf(). + +If your stdio requires an 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 identifier may not be longer than 255 characters, and no +component of your PATH may be longer than 255 if you use B<-S>. A regular +expression may not compile to more than 32767 bytes internally. + +Perl actually stands for Pathologically Eclectic Rubbish Lister, but +don't tell anyone I said that. + +=head1 NOTES + +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 principle virtues of a programmer are Laziness, +Impatience, and Hubris. See the Camel Book for why. |