Patent US 5,212,697

A variable length character string detection apparatus comprises a character collating part which registers a character string and compares each character of an input character string with each character making up the registered character string so as to output character string collating signals which respectively indicate whether or not each character of the input character string coincides with one of the characters making up the registered character string, a partial character string detecting part for carrying out predetermined logic operations on the character string collating signals and for outputting partial character string collating signals which respectively indicate whether or not the registered character string which coincides with the input character string and partial character strings thereof exist, and a detection pattern control part for carrying out a predetermined logic operation on the partial character string collating signals and for outputting collating result signals which respectively indicate whether or not the registered character string which coincides with the input character string, the partial character strings thereof and erroneous character strings exist.