For a lot of functions "useful" will be dependant on what you are using perl to do. I have been flirting with perl for 4 or 5 years now and never used dbmopen until earlier this week when I had cause to "grep" through a dbmfile, finding the right function and an example of its use was a matter of picking up the perl cookbook but a trip to the monastery or even your favourite search engine would have been just as rewarding.

I suggest you let your programming projects guide your learning and add to it liberally by reading as much as possible, the Monastery is a great place to start that :)

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my $chainsaw = 'Perl';