s/(.)?^O/\1/g; s/(.)?^N/\1/g;
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>perl -wMstrict -le
"for my $str (@ARGV) {
   printf q{%s -> }, $str;
   $str =~ s/(.)?^O/\1/g;
   $str =~ s/(.)?^N/\1/g;
   print $str;
   }
"  OhNoOhNo  NotOnNotOn
\1 better written as $1 at -e line 1.
\1 better written as $1 at -e line 1.
Use of uninitialized value $1 in substitution iterator at -e line 1.
OhNoOhNo -> hNoOhNo
Use of uninitialized value $1 in substitution iterator at -e line 1.
NotOnNotOn -> otOnNotOn
[download]