in reply to matching a line from one file in another

You can also just use the *nix command-line utility join (it supports reading from STDIN) .. 
join - hosts.txt                     # and type/paste in the input
./some_program | join - hosts.txt    # pipe the input in

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Re^2: matching a line from one file in another
by Thelonius (Priest) on Apr 14, 2006 at 19:06 UTC
    But remember that both input files need to be sorted. The examples were, but if not, you would have to sort them before the join.
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