perl is (or at least was) a very good language to know. some people would say that it's a dying language and is being replaced by Python. one of those two would be worth your time.
i'd say to hell with PHP, though. everyone and their brother knows PHP. anyone can build a webpage. you can learn it online if you need to so dont waste your time on it while in school.
at least a basic understanding of networking (TCP/IP) is necessary.
jephthah
Posting Maven
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Now learn at least one operating system internals e.g. unix . windows.
ithelp
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Salem
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