Just a nitpick: you only need parentheses when there's a capture, so you can remove them most of the times. 
(my $adj = $1) =~ s/\d/3/g;  # No parentheses needed.
($res = $str) =~ s{ (\d+) }{ ($adj = $1) =~ s/\d/3/g; $adj }xe;  # Par
+entheses only needed in the outer substitution.

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map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re^2: regex in REPLACEMENT in s/// by choroba
in thread regex in REPLACEMENT in s/// by perlboy_emeritus

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