note muba <p><i>The actual reason you aren't substituting properly is that you are printing @L1, but that array never gets modified by your substitution which acts on $line. </i></p> <p>Not true:</p> <c> my @L1 = qw(Abc aBc abC); for my $line (@L1) { $line =~ s/a/_/i; print "\@L1: <", join(", ", @L1), ">; \$line: <$line>\n"; } __END__ @L1: <_bc, aBc, abC>; $line: <_bc> @L1: <_bc, _Bc, abC>; $line: <_Bc> @L1: <_bc, _Bc, _bC>; $line: <_bC> </c> 977513 977518