#!/bin/bash
#
# File: trap.sh
# 
# Description: A script to understand the trap command and signal handling.
# The script first creates a file in /tmp and sets up the trap command to
# rm the file if the user enters a control-c (INT signal) at the terminal.
# The second part of the script executed once the user enters a control-c
# resets the trap command to NULL (no action)  
#
# Input: control-c (INT) from user.
#
# Output: Prints out whether the created file exists or not.
#
# Modified from Linux Programming (Matthews, Stones)
#

trap 'rm -f /tmp/myfile_$$' INT
echo create file /tmp/myfile_$$
date > /tmp/myfile_$$

printf "Press control-c to interrupt ...\n"

while [ -f /tmp/myfile_$$ ]; do 
    printf "File /tmp/myfile_$$ exists\n"
    sleep 1
done

ls  /tmp/myfile_$$

printf "See the file /tmp/myfile_$$ does not exist\n"

# This time around the trap is reset to no action.
# The control-c forces the script to end because there is no action. 
# The default behavior is to immediately terminate the script if there
# is no command associated with the trap.

trap INT                            
echo create file /tmp/myfile_$$
date > /tmp/myfile_$$

printf "Press control-c to interrupt ...\n"

while [ -f /tmp/myfile_$$ ]; do 
    printf "File /tmp/myfile_$$ exists\n"
    sleep 1
done

ls  /tmp/myfile_$$

printf "See the file /tmp/myfile_$$ does not exist\n"

exit 0