string-length will place the number of bytes in <string> into number <length>.
Note that <string> does not need to be null-terminated, meaning it can be a binary or text string. <length> is the number of bytes comprising any such string.
Examples
Variable "len" will be 6:
set-string str = "string" string-length str to len
Variable "len2" will be 18 - the string has a null character in the middle of it:
set-string str2 = "string""\x00 after null" string-length str2 to len2
