http://www.perlmonks.org?node_id=1016575


in reply to contextual substitution with s///?

Capture what should remain, not what should change: 
$s =  "test string x  x\nFeb  1 09:12:33  (";
$s =~ s/^(\w{3})  /$1 /m;

[download]
Also note that if you are matching multiline string, the /m modifier is needed to match after a newline.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In Section Seekers of Perl Wisdom