1O(3pm) Perl Programmers Reference Guide O(3pm)
2
6 O - Generic interface to Perl Compiler backends
7
9 perl -MO=[-q,]Backend[,OPTIONS] foo.pl
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12 This is the module that is used as a frontend to the Perl Compiler.
13 If you pass the "-q" option to the module, then the STDOUT filehandle
15 will be redirected into the variable $O::BEGIN_output during compila‐
16 tion. This has the effect that any output printed to STDOUT by BEGIN
17 blocks or use'd modules will be stored in this variable rather than
18 printed. It's useful with those backends which produce output them‐
19 selves ("Deparse", "Concise" etc), so that their output is not confused
20 with that generated by the code being compiled.
21 The "-qq" option behaves like "-q", except that it also closes STDERR
23 after deparsing has finished. This suppresses the "Syntax OK" message
24 normally produced by perl.
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27 Most compiler backends use the following conventions: OPTIONS consists
28 of a comma-separated list of words (no white-space). The "-v" option
29 usually puts the backend into verbose mode. The "-ofile" option gener‐
30 ates output to file instead of stdout. The "-D" option followed by var‐
31 ious letters turns on various internal debugging flags. See the docu‐
32 mentation for the desired backend (named "B::Backend" for the example
33 above) to find out about that backend.
34
36 This section is only necessary for those who want to write a compiler
37 backend module that can be used via this module.
38 The command-line mentioned in the SYNOPSIS section corresponds to the
40 Perl code
41 use O ("Backend", OPTIONS);
43 The "import" function which that calls loads in the appropriate
45 "B::Backend" module and calls the "compile" function in that package,
46 passing it OPTIONS. That function is expected to return a sub reference
47 which we'll call CALLBACK. Next, the "compile-only" flag is switched on
48 (equivalent to the command-line option "-c") and a CHECK block is reg‐
49 istered which calls CALLBACK. Thus the main Perl program mentioned on
50 the command-line is read in, parsed and compiled into internal syntax
51 tree form. Since the "-c" flag is set, the program does not start run‐
52 ning (excepting BEGIN blocks of course) but the CALLBACK function reg‐
53 istered by the compiler backend is called.
54 In summary, a compiler backend module should be called "B::Foo" for
56 some foo and live in the appropriate directory for that name. It
57 should define a function called "compile". When the user types
58 perl -MO=Foo,OPTIONS foo.pl
60 that function is called and is passed those OPTIONS (split on commas).
62 It should return a sub ref to the main compilation function. After the
63 user's program is loaded and parsed, that returned sub ref is invoked
64 which can then go ahead and do the compilation, usually by making use
65 of the "B" module's functionality.
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68 The "-q" and "-qq" options don't work correctly if perl isn't compiled
69 with PerlIO support : STDOUT will be closed instead of being redirected
70 to $O::BEGIN_output.
71
73 Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
74perl v5.8.8 2001-09-21 O(3pm)