O(3p)            Perl Programmers Reference Guide           O(3p)


NAME
       O - Generic interface to Perl Compiler backends

SYNOPSIS
               perl -MO=[-q,]Backend[,OPTIONS] foo.pl

DESCRIPTION
       This is the module that is used as a frontend to the Perl
       Compiler.

       If you pass the "-q" option to the module, then the STDOUT
       filehandle will be redirected into the variable
       $O::BEGIN_output during compilation.  This has the effect
       that any output printed to STDOUT by BEGIN blocks or use'd
       modules will be stored in this variable rather than
       printed. It's useful with those backends which produce
       output themselves ("Deparse", "Concise" etc), so that
       their output is not confused with that generated by the
       code being compiled.

       The "-qq" option behaves like "-q", except that it also
       closes STDERR after deparsing has finished. This sup-
       presses the "Syntax OK" message normally produced by perl.

CONVENTIONS
       Most compiler backends use the following conventions:
       OPTIONS consists of a comma-separated list of words (no
       white-space).  The "-v" option usually puts the backend
       into verbose mode.  The "-ofile" option generates output
       to file instead of stdout. The "-D" option followed by
       various letters turns on various internal debugging flags.
       See the documentation for the desired backend (named
       "B::Backend" for the example above) to find out about that
       backend.

IMPLEMENTATION
       This section is only necessary for those who want to write
       a compiler backend module that can be used via this mod-
       ule.

       The command-line mentioned in the SYNOPSIS section corre-
       sponds to the Perl code

           use O ("Backend", OPTIONS);

       The "import" function which that calls loads in the appro-
       priate "B::Backend" module and calls the "compile" func-
       tion in that package, passing it OPTIONS. That function is
       expected to return a sub reference which we'll call CALL-
       BACK. Next, the "compile-only" flag is switched on (equiv-
       alent to the command-line option "-c") and a CHECK block
       is registered which calls CALLBACK. Thus the main Perl
       program mentioned on the command-line is read in, parsed
       and compiled into internal syntax tree form. Since the



perl v5.8.8                 2002-10-27                          1





O(3p)            Perl Programmers Reference Guide           O(3p)


       "-c" flag is set, the program does not start running
       (excepting BEGIN blocks of course) but the CALLBACK func-
       tion registered by the compiler backend is called.

       In summary, a compiler backend module should be called
       "B::Foo" for some foo and live in the appropriate direc-
       tory for that name.  It should define a function called
       "compile". When the user types

           perl -MO=Foo,OPTIONS foo.pl

       that function is called and is passed those OPTIONS (split
       on commas). It should return a sub ref to the main compi-
       lation function.  After the user's program is loaded and
       parsed, that returned sub ref is invoked which can then go
       ahead and do the compilation, usually by making use of the
       "B" module's functionality.

BUGS
       The "-q" and "-qq" options don't work correctly if perl
       isn't compiled with PerlIO support : STDOUT will be closed
       instead of being redirected to $O::BEGIN_output.

AUTHOR
       Malcolm Beattie, "mbeattieATsable.uk"
































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