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O(3)
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 "import" function which that calls loads in the appropriate
  "B::Backend" module and calls the "compile" function in that package,
  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@sable.ox.ac.uk"

Index for Section 3

Alphabetical listing for O

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