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bashsignalsbash-trap

bash trap will echo from keyboard Ctrl-C while not kill 2

Say I have a script:

#!/bin/bash
# test_trap.sh

trap "echo SIGINT captured!" SIGINT
echo $$

sleep 1000

I know trap COMMAND will only be executed after sleep 1000 finishes when it receives SIGINT signal. But the command of trap will be executed when I pressed keyboard Ctrl-C:

> sh test_sh.sh
50138
^CSIGINT captured!

And using kill -s SIGINT will not.

What am I missing here?

The bash version is GNU bash, 4.2.46(2)-release

Solution

  • With kill -s SIGINT 50138, you are only sending the signal to the shell's process, and that has to wait for sleep 1000 to finish, because sleep doesn't receive the signal.

    Control-C, though, causes the terminal to send SIGINT to every process in the current process group, so both your shell script and sleep receive it. Your script still doesn't process the trap command until sleep completes, but sleep exits immediately in response to the SIGINT it just received from the terminal.

    If your kill supports it, you can also use kill -s SIGINT -50138 (note the negative process id) to send SIGINT to the entire process group.