Trapping signal from shell script... doesn't seem to work?

Aitor San Juan asanjuan at
Wed Feb 7 15:30:38 UTC 2007

Hi list!

I have written a Bourne shell script. This shell script invokes a
program written in the C language.

Below is basically the shell script source code. As you can see,
the C program is not invoked in the background, but in the
foreground, so the shell script doesn't finish until the C program
has finished.

I want the shell script to trap TERM or INT signals, so when any
of these are raised, the shell script will try to send SIGTERM to
the program "myprog":

user1:/usr/home/user1$ ps -ax | grep -v grep | grep myprog
22406  p0  I+     0:00.01 /bin/sh ../cronjobs/
22449  p0  I+     0:00.00 /usr/home/user1/myprog -d

user1:/usr/home/user1$ kill -TERM 22406

user1:/usr/home/user1$ ps -ax | grep -v grep | grep myprog
22406  p0  S+     0:00.01 /bin/sh ../cronjobs/
22449  p0  I+     0:00.00 /usr/home/user1/myprog -d

I notice the change in state of the shell script process from I+
to S+, but nothing else happens. The shell script seems to remain
in execution. However as soons as I press Ctrl-C at the terminal
where I invoked the shell script, it indeed receives the Ctrl-C,
but "myprog" receives it first so when the function "trap_handler"
executes, there is no "myprog" process in memory.

My question: Can anybody tell me what happens and/or what am I
doing wrong? Why must I press Ctrl-C to force the shell script to
finally receive the TERM signal when I executed the kill command
from another session? What is this apparent delay due to?

Thanks in advance.

#------------------ SHELL SCRIPT BEGIN ------------------
trap_handler() {
    echo "*** SYSTEM SIGNAL RECEIVED ***"
    echo "$1 caught. Ending..."
    kill -TERM $pid
    exit 1

trap 'trap_handler SIGINT' INT
trap 'trap_handler SIGTERM' TERM

/usr/home/user1/myprog -d
#------------------ SHELL SCRIPT END ------------------

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