Programming Perl, 4th Edition

The Bytecode Generator

The B::Bytecode module writes the parse tree’s opcodes out in a platform-independent encoding. You can take a Perl script compiled down to bytecodes and copy that to any other machine with Perl installed on it.

The currently experimental perlcc(1) command from the CPAN B::C distribution knows how to convert Perl source code into a byte-compiled Perl program. All you have to do is:

% perlcc –B –o pbyscript srcscript

And now you should be able to directly “execute” the resulting pbyscript. The start of that file looks somewhat like this:

#!/usr/bin/perl
use ByteLoader 0.03;
^C^@^E^A^C^@^@^@^A^F^@^C^@^@^@^B^F^@^C^@^@^@^C^F^@^C^@^@^@
B^@^@^@^H9^A8M–^?M–^?M–^?M–^?7M–^?M–^?M–^?M–^?6^@^@^@^A6^@
^G^D^D^@^@^@^KR^@^@^@^HS^@^@^@^HV^@M–2<W^FU^@^@^@^@X^Y@Z^@
...

There you find a small script header followed by purely binary data. This may seem like deep magic, but its dweomer, er, dwimmer is at most a minor one. The ByteLoader module uses a technique called a source filter to alter the source code before Perl gets a chance to see it. A source filter is a kind of preprocessor that applies to everything below it in the current file. Instead of being limited to simplistic transformations the way macro processors like cpp(1) and m4(1) are, here there are no constraints. Source filters have been used to augment Perl’s syntax, to compress or encrypt source code, even to write Perl programs in Latin. E perlibus unicode; cogito, ergo substr; carp dbm, et al. Er, caveat scriptor.

The ...