perl -e '$x = "abcde";             $x =~ s/b../==${^MATCH}==/p;  print "$x Match:${^MATCH}\n"'
a====e Match:bcd
perl -e '$x = "abcde"; $sub="b.."; $x =~ s/$sub/==${^MATCH}==/p; print "$x Match:${^MATCH}\n"'
a==bcd==e Match:bcd