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I just took notice to this generated by Catalyst.pl. It is obviously some sort of unannotated hack. What is the advantage of setting up a version string like this? I can't even figure out what they're trying to do.
our $VERSION = '0.01'; $VERSION = eval $VERSION; 
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eval in all its forms is used to execute a little Perl program, trapping any errors encountered so they don't crash the calling program.
The eval block is parsed with the rest of the code and its return value is a reference to the array @a . That reference is assigned to $ttt . While the eval block goes out of scope, @a still has a non-zero reference count (thanks to $ttt ) so it still exists.
$@ The Perl syntax error or routine error message from the last eval, do-FILE, or require command. If set, either the compilation failed, or the die function was executed within the code of the eval.
Version numbers are complex in Perl. Here's an excellent overview for those looking for the gory details. It might surprise you how many subtle ways there are to get things wrong...
The direct answer to your question though, is that different things expect different formats. For CPAN, you care about development versions for example, as a string. For runtime, you care about them as a number.
Consider the case of $VERSION = "0.01_001". eval converts it to the number 0.01001 correctly.
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