As mentioned, there is a unix split command:

user@host ~$] split -l 30 bigfile.txt
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Can also do this in a perl oneliner (warning -- this one is very inefficient):

perl -ne 'open FILE, ">>", "smallfile".int($./30).".txt"; print FILE $
+_; close FILE }' bigfile.txt
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Take a look at the $. entry in perlvar.