Return the substring of s which starts at character number offset and is len characters long.
If offset is negative, extraction starts that far from the end of the string. If len is omitted, the substring extends to the end of S.
For example,
substr ("This is a test string", 6, 9) "is a test"This function is patterned after AWK. You can get the same result by s
(
offset: (
offset+
len- 1))
.