Proof-of-concept script that begins synchronously then goes asynchronous. Meant to be called via SSH, executes some instructions synchronously, launches a long asynchronous task (e.g. download), wait a few seconds to ensure that said taks didn't fail immediately, then ends the SSH connection. See http://serverfault.com/questions/524738/remote-sy…

sync-async.sh

#! /usr/bin/env bash

function closefd() {
	exec 0>&- # close stdin
	exec 0<&-
	exec 1>&- # close stdout
	exec 1<&-
	exec 2>&- # close stderr
	exec 2<&-	
}

if [[ $1 == "-do" ]]; then
	closefd  # release SSH connection, part 2/2 (child)
	# asynchronous task
	sleep 30 &&
		echo $2 >/tmp/ok
else
	# preliminary-synchronous-commands &&
	nohup $0 -do $1 &
	sleep 5	# ensure it didn't immediately fail
	if ! kill -0 $!; then
		echo "Cannot find PID"
		exit 1
	else
		echo "PID found, exiting"
		closefd  # release SSH connection, part 1/2 (parent)
		exit 0
	fi
fi

&& (chains commands only if they are successful / have a return status of 0) can be omitted when

set -e

is specified before.