O - phpMan

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 suppresses 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 module.

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

        use O ("Backend", OPTIONS);

    The "O::import" function loads the appropriate "B::Backend" module and
    calls its "compile" function, passing it OPTIONS. That function is
    expected to return a sub reference which we'll call CALLBACK. Next, the
    "compile-only" flag is switched on (equivalent 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 "-c" flag is set,
    the program does not start running (excepting BEGIN blocks of course)
    but the CALLBACK function 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 directory 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 compilation 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, "mbeattie AT sable.uk"

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