in reply to Standardising code documentation
It's easier to test smaller components, and there are also other situations where you might want to run just a subset of a larger process (for instance if you had a script which fetched a file, parsed it and inserted it in the database, you might want to just parse and insert it if the fetch succeeded and the parse failed). Of course command-line switches can be used limit operations as well.
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Seekers of Perl Wisdom