Question

I am trying to understand some sample code describing signal handling in bash. In Example 32-7 at http://tldp.org/LDP/abs/html/debugging.html, the writer’s comments state that he is capturing a SIGINT, yet the trap is for EXIT.

{
     trap "exit" SIGUSR1
     sleep $interval; sleep $interval
     while true; do
         ...
     done; } &         # Start a progress bar as a background process.

pid=$!
trap "echo !; kill -USR1 $pid; wait $pid"  EXIT        # To handle ^C.

Why does a trap of EXIT send the correct signal (SIGUSR1) to the backgroud process on a SIGINT (Ctl-C)?

Any help is appreciated explaining why this works.

Answer 1

The EXIT pseudo-signal is raised both on normal exit and when the script is being interrupted.