How to remove empty lines from beginning and end of file?

I would like to remove empty lines from the beginning and the end of file, but not remove empty lines between non-empty lines in the middle. I think sed or awk would be the solution. Source: 1: 2: 3:line1 4: 5:line2 6: 7: 8: Output: 1:line1 2: 3:line2