Some references that may prove useful:

• Minimal Perl for UNIX and Linux People excellent book by Tim Maher.
• Perl Testing: A Developer's Notebook another excellent book, this time by Ian Langworth and chromatic (this one is relevant since you mentioned the need to test Unix programs).
• Course Notes from Perl Training Australia. In particular, their "Perl for System Administration" seems highly relevant.
• UNIX 'command' equivalents in Perl. Recent PM node showing the Perl equivalents of various Unix commands.