stop currently running bash script lazily/gracefully

Question

Say I have a bash script like this:

#!/bin/bash
exec-program zero
exec-program one

the script issued a run command to exec-program with the arg "zero", right? say, for instance, the first line is currently running. I know that Ctrl-C will halt the process and discontinue executing the remainder of the script.

Instead, is there a keypress that will allow the current-line to finish executing and then discontinue the script execution (not execute "exec-program one") (without modifying the script directly)? In this example it would continue running "exec-program zero" but after would return to the shell rather than immediately halting "exec-program zero"

TL;DR Something runtime similar to "Ctrl-C" but more lazy/graceful ??

Answer 1

In the man page, under SIGNALS section it reads:

If bash is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed until the command completes.

This is exactly what you're asking for. You need to set an exit trap for SIGINT, then run exec-program in a subshell where SIGINT is ignored; so that it'll inherit the SIG_IGN handler and Ctrl+C won't kill it. Below is an implementation of this concept.

#!/bin/bash -
trap exit INT
foo() (
  trap '' INT
  exec "$@"
)

foo sleep 5
echo alive

If you hit Ctrl+C while sleep 5 is running, bash will wait for it to complete and then exit; you will not see alive on the terminal.

exec is for avoiding another fork() btw.