In Linux, we have a great tool to do it: trap. The following script sets a handler up by means of the trap command. Its first parameter is the function or code which manages the exception, and the second one, the name (SEGV) or value (11) of the signal. We can also add more signals to the same trap.
[root@localhost ~]# cat segfault.sh
#!/bin/bash
function trap_segfault
{
echo "We have a segmenation fault!"
# Reset handler
trap - 11
exit 127
}
# Start handler
trap 'trap_segfault' 11
# Here code which can produce a segmentation fault, such as:
kill -SEGV $$ 1>&2
Apart from catching segmentation faults, we can use this technique so as to treat other signals inside a bash script. In order to take a look at all the signals provided by Linux, you might run 'trap -l' or 'kill -l'. But if you want to extend the information about them, you will have to resort to the own man.
[root@localhost ~]# man 7 signal
...
Signal Value Action Comment
──────────────────────────────────────────────────────────────────────
SIGHUP 1 Term Hangup detected on controlling terminal
or death of controlling process
SIGINT 2 Term Interrupt from keyboard
SIGQUIT 3 Core Quit from keyboard
SIGILL 4 Core Illegal Instruction
SIGABRT 6 Core Abort signal from abort(3)
SIGFPE 8 Core Floating point exception
SIGKILL 9 Term Kill signal
...
Next example handles SIGHUP to show the PID of the script and SIGINT to terminate it.
[root@localhost ~]# cat hup_int.sh
#!/bin/bash
function trap_sigint
{
echo "Script terminated"
# Reset handlers
trap - HUP INT
exit 0
}
# Start handlers
trap 'echo PID: $$\n' HUP
trap 'trap_sigint' INT
while [ true ];
do
sleep 1
done
[root@localhost ~]# ./hup_int.sh &
[1] 3046
[root@localhost ~]# kill -HUP 3046
[root@localhost ~]# PID: 3046
[root@localhost ~]# kill -INT 3046
[root@localhost ~]# Script terminated
And finally, also say that we can use this utility to leave out signals. For instance, the following order makes the script ignore SIGTERM.
trap : SIGTERM
