A substring defines a portion of a string variable or string array element. It is selected by specifying a starting position within the string value and optionally, either the length of the sub-string, or the ending position within the string value. If only the starting position is specified, the rest of the string value from that point on is used for the sub-string. String positions are one-based, i.e., the first character of a string is in position one.
The beginning position must be at least one and no greater than the current length plus one. When only the beginning position is specified, the substring includes all characters from that position to the current end of the string.
The ending position must be no less than the beginning position minus one and no greater than the dimensioned length of the string. When both beginning and ending positions are specified, the substring includes all characters from the beginning position to the ending position or current end of the string, whichever is less.
The maximum substring length must be at least zero and no greater than one plus the dimensioned length of the string minus the beginning position. When a beginning position and substring length are specified, the substring starts at the beginning position and includes the number of characters specified by the substring length. If there are not enough characters available, the substring includes only the characters from the beginning position to the current end of the string.
