O - Generic interface to Perl Compiler backends


        perl -MO=Backend[,OPTIONS]


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


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.


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 an END 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

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.


Malcolm Beattie,


We are painfully aware that these documents may contain incorrect links and misformatted HTML. Such bugs lie in the automatic translation process that automatically created the hundreds and hundreds of separate documents that you find here. Please do not report link or formatting bugs, because we cannot fix per-document problems. The only bug reports that will help us are those that supply working patches to the installhtml or pod2html programs, or to the Pod::HTML module itself, for which I and the entire Perl community will shower you with thanks and praises.

If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.

--Tom Christiansen, Perl Documentation Compiler and Editor

Return to the Perl Documentation Index.
Return to the Perl Home Page.