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How do I select a random line from a file?

by faq_monk (Initiate)
on Oct 13, 1999 at 03:42 UTC ( [id://820] : perlfaq nodetype . print w/replies, xml ) Need Help??

Current Perl documentation can be found at

Here is our local, out-dated (pre-5.6) version:

Here's an algorithm from the Camel Book:

    rand($.) < 1 && ($line = $_) while <>;

This has a significant advantage in space over reading the whole file in. A simple proof by induction is available upon request if you doubt its correctness.