Perl ‘Practical Extraction and Report Language’
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 some of the best features other programming languages 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 (previously called ""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 hashes. Setuid Perl scripts are safer than C programs through a dataflow tracing mechanism which prevents many stupid security holes.
Perl version 5 is nearly a complete rewrite, and provides the following additional benefits:
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 -w switch!!! Whenever you don't get mysterious behavior, try using -w anyway.
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.
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''. Anonymous subroutines exhibit deep binding of lexical variables (closures).
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.
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.
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.
Embeddable 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, and Perl itself can be made into a dynamic library.
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.
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 -p or -n switches.
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.
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 for just autoloading.
Regular expression enhancements You can now specify nongreedy 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.
Innumerable Unbundled Modules The Comprehensive Perl Archive Network described in the perlmodlib manpage contains hundreds of plug-and-play modules full of reusable code. See http://www.perl.com/CPAN for a site near you.
Compilability While not yet in full production mode, a working perl-to-C compiler does exist. It can generate portable byte code, simple C, or optimized C code.
