perl -e '$x = "abcde";             $x =~ s/b../==${^MATCH}==/p;  print "$x\n"'
perl -e '$x = "abcde"; $sub="b.."; $x =~ s/$sub/==${^MATCH}==/p; print "$x\n"'
 
##</code><code>##

a====e
a==bcd==e