Question

I have a script that is supposed to trap SIGTERM and SIGTSTP. This is what I have in the main block:

trap 'killHandling' TERM

And in the function:

killHandling () {
    echo received kill signal, ignoring
    return
}

… and similar for SIGINT. The problem is one of user interface. The script prompts the user for some input, and if the SIGTERM or SIGINT occurs when the script is waiting for input, it’s confusing. Here is the output in that case:

Enter something:     # SIGTERM received
received kill signal, ignoring

      # shell waits at blank line for user input, user gets confused
      # user hits "return", which then gets read as blank input from the user
      # bad things happen because of the blank input

I have definitely seen scripts which handle this more elegantly, like so:

Enter something:     # SIGTERM received
received kill signal, ignoring
Enter something:     # re-prompts user for user input, user is not confused

What is the mechanism used to accomplish the latter? Unfortunately I can’t simply change my trap code to do the re-prompt as the script prompts the user for several things and what the prompt says is context-dependent. And there has to be a better way than writing context-dependent trap functions.

I’d be very grateful for any pointers. Thanks!

Answer 1

The answer CodeGnome gave works, but as he points out, it is not robust; a second control-c causes undesirable behavior. I ultimately got around the problem by making better use of existing input validation in the code. So my interrupt handling code now looks like this:

killHandling () {
   echo received kill signal, ignoring
   echo "<<Enter>> to continue"
   return
}

Now the cursor still waits at a blank line for user input, but the user is not confused, and hits the “Enter” key as prompted. Then the script’s input validation detects that a blank line has been entered, which is treated as invalid input, and the user is re-prompted to enter something.

I remain grateful to CodeGnome for his suggestions, from which I learned a couple of things. And I apologize for the delay in posting this answer.