The SCAN operation scans a character string (base string) contained in factor 2 for a substring (compare string) contained in factor 1. The scan begins at a specified location contained in factor 2 and continues for the length of the compare string which is specified in factor 1.The result field contains the numeric value of the leftmost position of the compare string in the base string.
The CHECK operation verifies that each character in the base string (factor 2) is among the characters indicated in the comparator string (factor 1). Verifying begins at the leftmost character of factor 2 and continues character by character, from left to right. Each character of the base string is compared with the characters of factor 1. If a match for a character in factor 2 exists in factor 1, the next base string character is verified. If a match is not found, an integer value is placed in the result field to indicate the position of the incorrect character.

CHECK, scan, Mainframes