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I have read that when you press Ctrl+C a SIGINT signal will be sent to the foreground process group.
Can you give me an example of how I can have two or more processes in the foreground process group, because I want to see if all processes will terminate if I press Ctrl+C.
Since new processes all belong to the same process group, that of the parent process, have a process start a bunch of processes (fork), and then with appropriate logging and a delay, type Ctrl+C. They all eat a SIGINT.
$ perl -E 'fork for 1..2;say "ima $$"; $SIG{INT}=sub{die "woe $$\n"}; sleep 999'
ima 80920
ima 80922
ima 80921
ima 80923
^Cwoe 80920
woe 80922
woe 80921
woe 80923
$
(Add strace or sysdig or such to see the system calls or signals involved.)
fork makes two processes from one process. The parent can but need not block by calling some wait function. The above perl processes do not block on anything, they just all go to sleep.
Ctrl+C one time to terminate both the parent and child processes (I tried it and it worked).
A pipeline is one job, with multiple processes:
(cat ; echo foo >&2) | (cat ; echo bar >&2 )
If you end the input with Ctrl+D, you get the foo and bar output, if you kill the pipeline with Ctrl+C, neither is printed.
One example:
bash-4.3$ ( ( sleep 2 & (ps -Hfj | sh -c cat; perl -MPOSIX -E 'say tcgetpgrp 0'; sleep 5;:);:);:)
UID PID PPID PGID SID C STIME TTY TIME CMD
chazelas 18631 3848 18631 18631 0 12:51 pts/7 00:00:00 /bin/zsh
chazelas 2184 18631 2184 18631 0 21:00 pts/7 00:00:00 bash --norc
chazelas 2430 2184 2430 18631 0 21:07 pts/7 00:00:00 bash --norc
chazelas 2431 2430 2430 18631 0 21:07 pts/7 00:00:00 bash --norc
chazelas 2432 2431 2430 18631 0 21:07 pts/7 00:00:00 sleep 2
chazelas 2433 2431 2430 18631 0 21:07 pts/7 00:00:00 bash --norc
chazelas 2434 2433 2430 18631 0 21:07 pts/7 00:00:00 ps -Hfj
chazelas 2435 2433 2430 18631 0 21:07 pts/7 00:00:00 sh -c cat
chazelas 2436 2435 2430 18631 0 21:07 pts/7 00:00:00 cat
2430
At the time ps was running, there were 7 processes in the 2430 process group: 3 subshell processes (bash), one running ps, one running sh, one running cat, one running sleep 1. Later on, the processes spawned to execute perl and sleep 5 would also be in that same group.
tcgetpgrp() confirms that 2430 was indeed the foreground process group of the terminal device, so upon pressing Ctrl+C, all the processes in that group would receive a SIGINT.
