Shell: How to use screen and wait for a couple of background processes in a shell script

I am writing a shell script for a couple of long running processes. First of all I need to run all commands in the screen session manager, so that the execution of a process does not end if a user has been disconnected. Later I need wait for some background processes, which has been created before, to end, so that the following process can start.

My question is how to start a开发者_Python百科 screen session in a shell script and wait for the background processes to end.

A google search for "scripting screen" gives this as the first result. It looks like you can create named screen sessions with screen -d -m -S nameOfSession. Then screen -X -S <session name> screen will create a window in the screen session 'nameOfSession.' You can communicate with this window 1 (i.e. give commands for this screen session window 1 to run) by using

screen -X -S test -p 1 stuff "your command here ^M"

The "your_command_here" is the command you want to run. The ^M is the carriage return control character (you type Ctrl-V then Enter/Return in a terminal). The ^M will essentially "press return/enter" so that the command is run in this screen session. Play around with it.

Since you want to wait for your commands to finish, I would suggest forking the processes, via the ampersand:

your_command & Immediately after, the process-id of the forked of process is in $!. You can wait for all background processes to finish running by running wait.

I would suggest the screen reference.

You can't invoke screen (or nohup) on the running process, you have to do screen script. You could however do what nohup does, trap SIGHUP and redirect output to a file.

exec > OUT 2>&1
trap '' 1

To wait for background processes, save the pid when you create it and then call wait

foo&
PID1=$!
bar&
PID2=$1
wait $PID1 $PID2

Or alternatively just wait for everything to finish.

foo&
bar&
wait