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

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

NNAAMMEE #

 O - Generic interface to Perl Compiler backends

SSYYNNOOPPSSIISS #

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

DDEESSCCRRIIPPTTIIOONN #

 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.

CCOONNVVEENNTTIIOONNSS #

 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 ffiillee 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.

IIMMPPLLEEMMEENNTTAATTIIOONN #

 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.

BBUUGGSS #

 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.

AAUUTTHHOORR #

 Malcolm Beattie, "mbeattie@sable.ox.ac.uk"

perl v5.36.3 2019-02-13 O(3p)