When a process is running and in between we kill the process, the process terminates instantly without doing anything further. A programmer who writes a program may want to do some tasks before a program actually terminates; for example, a clean up of the temporary directories created, saving applications' state, saving logs, and so on. In such a case, a programmer would like to listen to signals and do the required task before actually allowing you to terminate the process.

Consider the following shell script example:

#!/bin/bash
# Filename: my_app.sh
# Description: Reverse a file

echo "Enter file to be reversed"
read filename

tmpfile="/tmp/tmpfile.txt"
# tac command is used to print a file in reverse order
tac $filename > $tmpfile
cp $tmpfile $filename
rm $tmpfile

This program takes an input from a user file and then reverses the file content. This script creates a temporary file to keep the reversed content of the file and later copies it to the original file. At the end, it deletes...