Hi, I have the following script, which just kills itself. It sets a trap, but only takes it if the output is not redirected. Can anybody explain to me why?
$ cat test17 #!/usr/bin/env bash trap "echo caught signal 2" 2 trap -p # show the process group ps -eo pid,pgid,cmd | grep $$ # send the signal to the process group kill -2 -$$ rc=$? if [ $rc -ne 0 ]; then echo "$0: kill failed: $rc" >&2 fi echo done. When I run it without stdio redirection, I get this output: $ bash -x test17 + trap 'echo caught signal 2' 2 + trap -p trap -- 'echo caught signal 2' SIGINT + ps -eo pid,pgid,cmd + grep 8711 8711 8711 bash -x test17 8712 8711 ps -eo pid,pgid,cmd 8713 8711 grep 8711 + kill -2 -8711 ++ echo caught signal 2 caught signal 2 + rc=0 + '[' 0 -ne 0 ']' + echo done. done. When I run it with stdio redirection, the script is terminated at the kill: $ bash -x test17 2>&1 | tee 0312-29.out + trap 'echo caught signal 2' 2 + trap -p trap -- 'echo caught signal 2' SIGINT + grep 8714 + ps -eo pid,pgid,cmd 8714 8714 bash -x test17 8715 8714 tee 0312-29.out 8716 8714 ps -eo pid,pgid,cmd 8717 8714 grep 8714 $ echo $? 130 The same thing happens if I use signal 10 instead of 2: $ bash -x test18 + trap 'echo caught signal 10' 10 + trap -p trap -- 'echo caught signal 10' SIGUSR1 + ps -eo pid,pgid,cmd + grep 8773 8773 8773 bash -x test18 8774 8773 ps -eo pid,pgid,cmd 8775 8773 grep 8773 + kill -10 -8773 ++ echo caught signal 10 caught signal 10 + rc=0 + '[' 0 -ne 0 ']' + echo done. done. $ bash -x test18 2>&1 | tee 0312-34.out + trap 'echo caught signal 10' 10 User defined signal 1 13810~/w/1670/bin>bash -x test18 2>&1 | tee 0312-34.out + trap 'echo caught signal 10' 10 + trap -p trap -- 'echo caught signal 10' SIGUSR1 + grep 8784 + ps -eo pid,pgid,cmd 8784 8784 bash -x test18 8785 8784 tee 0312-34.out 8786 8784 ps -eo pid,pgid,cmd 8787 8784 grep 8784 $ echo $? 138
