Hello,
Let’s take the following script as an example:
#!/bin/bash
function greeting(){
echo "Enter your name"
read name
echo "Hi there ${name}"
}
# Call the function
greeting
With the above, we are expecting the user to enter their name and then greet them. However, the user could just press CTRL+C
or CTRL+Z
and exit the script.
To prevent that, we could use the trap
command and trap specific term signals. For example, CTRL+Z
sends the SIGTSTP
signal, and CTRL+C
sends SIGINT
.
So if we wanted to prevent the user from exiting the script with CTRL+Z
or CTRL+C
, we could use the trap
command and trap those signals:
#!/bin/bash
function greeting(){
# Start the trap
trap ' ' SIGTSTP SIGINT SIGTERM
echo "Enter your name"
read name
echo "Hi there ${name}"
# End the trap
trap - SIGTSTP SIGINT SIGTERM
}
# Call the function
greeting
In case that you want to get a list of all term signals, you could use the following command:
trap -l
Output:
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
I personally prefer to use the numeric representation as follows:
...
trap ' ' 2 15 20
echo "Enter your name"
read name
echo "Hi there ${name}"
# End the trap
trap - 2 15 20
...
I hope that this helps!
Regards,
Bobby