The str-index function will return the position of a string inside another string.
Syntax
(str-index <lexeme-expression> <lexeme-expression>)
where the second argument is searched for the first occurrence of the first argument. The str-index function returns the integer starting position, counting from one, of the first argument in the second argument or returns the symbol FALSE if not found.
Example
CLIPS> (str-index "def" "abcdefghi") 4 CLIPS> (str-index "qwerty" "qwertypoiuyt") 1 CLIPS> (str-index "qwerty" "poiuytqwer") FALSE CLIPS>