D'oh! Actually the author was even more clever and figured out how to leave 'US' alone. Your solution breaks under strict though. Try this: 
my %tr = qw(U T u t);
s/\b([Uu])s\b/$tr{$1}hem/g;

[download]
BTW I would wonder about the author's solution working with Unicode...

In reply to RE: (tilly) 2: a simple substitution question by tilly
in thread a simple substitution question by d4vis

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