Heading translation in sed

• The other missing feature is that it treats all repeated characters like underlines

• The Perl program didn't

 I am a heading
 **************

 I am NOT a heading
 **************

 I am not a heading either
 ************************************

• Perl handled this:

 if (/^(.)1円+$/ && defined($held) && length($_) == length($held)) {

• sed has no (easy) way to compare the lengths of two strings