# <!-- parent=/index -->
my $re1 = qr(^\Q<!--\E\s?(\w+)=(.+)\s?\Q-->\E$);
# parent=/index
my $re2 = qr(^(\w+)=(.+)$);

if ( $string =~ m/${re1}|${re2}/ ) {
  if ( length($1) and length($2) ) { 
  }
  elsif ( length($3) and length($4) ) {
  }