instrb

Searches "string_expression1" starting at position "integer_expression1" for the "integer_expression2" occurrence of "string_expression2". If "integer_expression1" is negative, then the search occurs backwards from the end of "string_expression1". Returns the position (byte number) where "string_expression2" was found.

instrb ( string_expression1, string_expression2 [ ,
 integer_expression1 [ , integer_expression2 ] ] )