sub match_all_letters {
  my( $match, $in ) = @_;
  my @letters = split( //, $match );

  return @letters == grep { index( $in, $_ ) != -1 } @letters;
}

__END__
  DB<2> x match_all_letters( "the" => "there" )
0  1
  DB<3> x match_all_letters( "zxd" => "there" )
0  ''
  DB<4> x match_all_letters( "theq" => "there" )
0  ''
  DB<5> x match_all_letters( "abcde" => "gcdabef" )
0  1