You want to read the Perl Cookbook, chapter 8 (File Contents), page 284-285.

For your convenience, I put the code that does what you want in here.

Solution: Use rand() and $. to decide which line to keep:

rand($.) < 1 && ($line = $_) while <>;
# $line is the random line
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This works because you have a 1/N chance for line N to be kept. For more explanations, get the book.

Extending this example to choosing a random word from an array of words is left as an exercise for the reader (I always wanted to say that!) ...

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com