Send a running function to background in bash

Question

As the title says, I want to send a running function to the background. Something like

function myfunc {
    some_command | while read line
    #some_command must be running indefinitely
    do
        #if some condition on ${line} satisfies
        #Do something and go to background
    done
}

Is it possible?

I know that it is possible to call a function directly & to directly run it in the background. That is pretty obvious. This is not duplicate of this.

Possible duplicate of [executing shell command in background from script](https://stackoverflow.com/questions/3683910/executing-shell-command-in-background-from-script) — Aserre, Jul 24 '17 at 15:19
Why are you trying to do this? You can call your function form a separated bash script an call this with an ampersand. Then your function is run in the background. — schorsch312, Jul 24 '17 at 15:21
Why not `while true; do if ...; then do_something & break; fi` — William Pursell, Jul 24 '17 at 15:31
@WilliamPursell I edited the question. Now it should be clear why I am asking. — Raghuram Vadapalli, Jul 24 '17 at 15:39
I don't know if you can send a function to the background. But you surely can send a process or the script to the background. You just need to send an SIGSTOP signal. — Aditya, Jul 24 '17 at 15:45
@Aditya SIGSTOP sends it to background and stops. I need it to be running in background. — Raghuram Vadapalli, Jul 24 '17 at 15:46
This really doesn't make any sense. The net effect is that `myfunc` runs in the background, but the caller waits until the first time 'some condition' is satisfied. To accomplish that, have the caller block on a read from a pipe, then run the function in the background and have it write to that pipe when the condition is met. — William Pursell, Jul 24 '17 at 15:47
@WilliamPursell Can you explain it clearly in an answer. The condition is on ${line} if that is not clear. — Raghuram Vadapalli, Jul 24 '17 at 15:50
What is it you want in the background? It's not at all clear why you don't just invoke the function in the background initially, or why you can't just do `if condition; then do_something & fi` and do something in the background. — William Pursell, Jul 24 '17 at 15:58

score 4 · Accepted Answer · answered Jul 24 '17 at 15:59

4

A simple command creates a process in background and waits for its termination, in your case the caller must continue when a condition is met asynchronously with callee which continues running.

This can be done with kill -STOP (caller blocks himself) and kill -CONT (callee unblock caller)

function myfunc {
    some_command | while read line
    #some_command must be running indefinitely
    do
        #if some condition on ${line} satisfies
        kill -CONT $$
    done & kill -STOP $$
}

answered Jul 24 '17 at 15:59

Nahuel Fouilleul

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FYI, the `function` keyword makes this code needlessly noncompliant with the POSIX sh specification -- it would be portable to a wider array of shells if the first line were `myfunc() {`, with the `function` keyword removed and the `()` syntax added. – Charles Duffy Jul 24 '17 at 17:27

Send a running function to background in bash

1 Answers1