here is the sample file i am using
<xxxx><xxxxx><xxxxx><AppEventTimeStamp>2006-05-02 09:25:00</AppEventTimeStamp><xxxx><xxxx>345</xxx><AppEventTimeStamp>2006-10-18 10:25:00</AppEventTimeStamp><xxxxxx><\xxxxxxxx>
The format i am searching for is "year-mon-day hour-min-sec"
Just change the search pattern present in the above link mentioned by misenkiser
sed 's/^.\([0-9]\{4\}-[0-9]\{2\}-[0-9]\{2\} [0-2][0-4]:[0-5][0-9]:[0-5][0-9]\).$/\1/' file name