http://www.perlmonks.org?node_id=1024261


in reply to change [A-Z] to U, [a-z] to L with one regex?

$r =~ s[([a-zA-Z])][$1 lt '[' ? 'U' : 'L']ge;;

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But this will be vastly more efficient:

$r =~ tr[A-Z][U];
$r =~ tr[a-z][L];

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