How to increase executions speed of loops.?

We cannot possibly say without seeing the script.

Corona688 is right, it's difficult to impossible to pull a statement out of the blue. But in general, the less you do in loops in loops in loops, and the more you do in programs like awk, sed, and friends - running them once, using smart input/outout selection, and refraining from multiple calls - the better and faster your job will be done.