Well if you've got more memory than sense, then this might suffice for your task at hand - 
open(BF, $tsv_data) or die("It ain't there ($tsv_data): $!\n");
@res = map { "$_\n" if /LONDON/ } split(/\n/, <BF>);
close(BF);

[download]
Grab everyline with 'LONDON' and stick on that ever useful newline. Not necessarily a 'better' way but certainly a quicker one ;o)
HTH

broquaint

In reply to Re: Processing slurped file. by broquaint
in thread Processing slurped file. by Jonathan

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