How to handle Ctrl + c in shell script? - bash

Question

I am trying to handle the ctrl + c in the shell script. I have code running in while loop but i am calling the binary from script and running it in background so when i want to stop the binary should stop. Code is below of hello.c
vim hello.c
#include <stdio.h>
int main()
{
while(1)
{
int n1,n2;
printf("Enter the first number\n");
scanf("%d",&n1);
printf("Enter the second number\n");
scanf("%d",&n2);
printf("Entered number are n1 = %d , n2 =%d\n",n1,n2);
}
}
Below is the Bash script which i used.
#/i/bin/sh
echo run the hello binary
./hello < in.txt &
trap_ctrlc()
{
ps -eaf | grep hello | grep -v grep | awk '{print $2}' | xargs kill -9
echo trap_ctrlc
exit
}
trap trap_ctrlc SIGHUP SIGINT SIGTERM
After starting the script the hello binary is running continuously. I have killed this binary from other terminal using kill -9 pid command.
I have tried this trap_ctrlc function but it not work. How to handle the Ctrl + c in shell script.
In in.txt i have added the input so i can pass this file directly to the binary
vim in.txt
1
2
Output:
Enter the first number
Enter the second number
Entered number are n1 = 1 , n2 =2
Enter the first number
Enter the second number
Entered number are n1 = 1 , n2 =2
Enter the first number
Enter the second number
Entered number are n1 = 1 , n2 =2
And it going continuously.

Answer 1

Change your c program so it checks if reading data actually succeeded:
#include <stdio.h>
int main()
{
int n1,n2;
while(1) {
printf("Enter the first number\n");
if(scanf("%d",&n1) != 1) return 0; /* check here */
printf("Enter the second number\n");
if(scanf("%d",&n2) != 1) return 0; /* check here */
printf("Entered number are n1 = %d , n2 =%d\n",n1,n2);
}
}
It will now terminate when the input from in.txt is depleted.
To make something that reads from in.txt many times, you could create a loop in your bash script that feeds ./hello forever (or until it's killed).
Example:
#!/bin/bash
# a function to repeatedly print the content in "in.txt"
function print_forever() {
while [ 1 ];
do
cat "$1"
sleep 1
done
}
echo run the hello binary
print_forever in.txt | ./hello &
pid=$!
echo "background process $pid started"
trap_ctrlc() {
kill $pid
echo -e "\nkill=$? (0 = success)\n"
wait $pid
echo "wait=$? (the exit status from the background process)"
echo -e "\n\ntrap_ctrlc\n\n"
}
trap trap_ctrlc INT
# wait for all background processes to terminate
wait
Possible output:
$ ./hello.sh
run the hello binary
background process 262717 started
Enter the first number
Enter the second number
Entered number are n1 = 1 , n2 =2
Enter the first number
Enter the second number
Entered number are n1 = 1 , n2 =2
Enter the first number
^C
kill=0 (0 = success)
wait=143 (the exit status from the background process)
trap_ctrlc
Another option can be to kill the child after the wait is interrupted:
#!/bin/bash
function print_forever() {
while [ 1 ];
do
cat "$1"
sleep 1
done
}
echo run the hello binary
print_forever in.txt | ./hello &
pid=$!
echo "background process $pid started"
trap_ctrlc() {
echo -e "\n\ntrap_ctrlc\n\n"
}
trap trap_ctrlc INT
# wait for all background processes to terminate
wait
echo first wait=$?
kill $pid
echo -e "\nkill=$? (0 = success)\n"
wait $pid
echo "wait=$? (the exit status from the background process)"`
``