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O(3) - O - Generic interface to Perl Compiler backends - man 3 O

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

       O - Generic interface to Perl Compiler backends

               perl -MO=[-q,]Backend[,OPTIONS]

       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 compila-
       tion.  This has the effect that any output printed to STDOUT by BEGIN
       blocks or use'd modules will be stored in(1,8) this variable rather than
       printed. It's useful with those backends which produce output them-
       selves ("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.

       Most compiler backends use the following conventions: OPTIONS consists
       of a comma-separated list of words (no white-space).  The "-v" option
       usually puts(3,n) the backend into verbose mode.  The "-ofile" option gener-
       ates output to file(1,n) instead of stdout. The "-D" option followed by var-
       ious letters turns on various internal debugging flags. See the docu-
       mentation for the desired backend (named(5,8) "B::Backend" for the example
       above) to find out about that backend.

       This section is only necessary for those who want to write(1,2) a compiler
       backend module that can be used via this module.

       The command-line mentioned in(1,8) the SYNOPSIS section corresponds to the
       Perl code

           use O ("Backend", OPTIONS);

       The "import" function which that calls loads in(1,8) the appropriate
       "B::Backend" module and calls the "compile" function in(1,8) 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 reg-
       istered which calls CALLBACK. Thus the main Perl program mentioned on
       the command-line is read(2,n,1 builtins) in(1,8), parsed and compiled into internal syntax
       tree form. Since the "-c" flag is set(7,n,1 builtins), the program does not start run-
       ning (excepting BEGIN blocks of course) but the CALLBACK function reg-
       istered by the compiler backend is called.

       In summary, a compiler backend module should be called "B::Foo" for
       some foo and live in(1,8) the appropriate directory for that name.  It
       should define a function called "compile". When the user types

           perl -MO=Foo,OPTIONS

       that function is called and is passed those OPTIONS (split(1,n) 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.

       The "-q" and "-qq" options don't work correctly if(3,n) perl isn't compiled
       with PerlIO support : STDOUT will be closed instead of being redirected
       to $O::BEGIN_output.

       Malcolm Beattie, ""

perl v5.8.5                       2001-09-21                              O(3)

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