Spell is the standard English language spell checker for Unix.Appearing in Version 7 Unix, spell was originally written by Stephen C. Johnson of Bell Labs in 1975. Douglas McIlroy later improved its accuracy, performance, and memory use, and described his work and spell in general in his 1982 paper "Development of a Spelling list".Spell has a simple command-line interface: It goes over all the words in a given text file, and prints a sorted list of unique misspelled words in that file.