The following commands report an error on equals lines because field outside sorting scope were not sorted
$ cat <<'.' | > AAA AAA > BBB BBB > ZZZ CCC > DDD DDD > BBC EEE > BBD EEE > BBC EEE > BBE EEE > CCC FFF > DDD GGG > EEE HHH > . > LANG=C sort -k 2,2 -c sort: -:7: disorder: BBC EEE
