How can I run multiple Bash scripts simultaneously in a terminal window?

Question

I need to run several Bash scripts (the same script with different variables to be precise) at the same time. To keep the number of tabs under control, I wish to group them in a single terminal tab.

The scripts regularly output, which I check for any problem.

If I send them to the background as

./script.sh 1 &
./script.sh 2 &
./script.sh 3 &
./script.sh 4

I will lose control over them. For example, I terminate the script by Ctrl+C. With the above code, I should find the pid for each process to kill them.

Note that the above code is the content of my main script (say ./all_scripts.sh) rather than commands to be typed in the terminal.

Is there a way to run the script in the same terminal while treating them as a single outputting script?

Answer 1

You don't lose control over them. You're sending them (other than the last one) to the background.

If you run the command chain you specify, the invocation ./script.sh 4 will be in the foreground, and the other scripts will be running in the background. Input will be sent to the foreground script. To suspend the foreground script, press CtrlZ. To send the suspended script to the background to continue running, use the bg command.

To see the scripts (or more correctly, jobs) you have and the states they're in, use jobs.

To bring a specific job to the fore, use fg and its number (as reported by the aforementioned jobs) with a % prefix, e. g. fg %2. To terminate a specific job, you can either bring it to the foreground with fg and terminate it sanely, or you can kill it, e. g. kill -TERM %2.

Answer 2

After testing different methods and programs, I found that the pragmatic solution is GNU Parallel. I post this answer as it may help others.

GNU Parallel has not been built for this task, but perfectly serves the purpose.

If running the scripts as

parallel -u ::: './script.sh 1' './script.sh 2' #(and so forth)

All scripts will be run in parallel.

The -u (--ungroup) flag sends the script outputs into stdout while executing the scripts.

Ctrl+C kills the parallel job, and subsequently all running scripts.

Answer 3

You can use tmux for this.

It is a terminal multiplexer meaning that it splits one tab into multiple windows.

• Start it with the command tmux.
• Use Contr+B followed by " or % in order to split a pane into two panes.
• Start processes in the foreground.
• Switch between the processes uding Contr+B followed by arrow keys.

Now you have normal control over multiple processes in one tab of your terminal.

If you want to focus (or unfocus) a specific pane, use Contr+B followed by Z.

If you need to scroll use Contr+B followed by Q and scroll using arrow keys(or activate mouse mode).

You can find a cheatsheet here.

It is also possible to automate that process.

Answer 4

You can redirect the output to a file (one per process or a combined one). Having one file for all is not a problem if the writes are small (512 byte is safe, probably even 4K). Small writes are atomic:

./script.sh 1 >output.1 2>&1 &
./script.sh 2 >output.2 2>&1 &
./script.sh 3 >output.3 2>&1 &
./script.sh 4 >output.4 2>&1 &
./script.sh 5 >output.5 2>&1 &

while wait % >/dev/null 2>&1; do : ; done

If you are doing that interactively then the following may help: You can easily address the jobs by prepending a (otherwise useless) environment variable definition (like BackGround Task ID):

bgtid=foo ./script.sh 1 &
[...]
kill %bgtid=foo

The command prefix just must be unambigeous (so no bgtid=foo and bgtid=foobar).

Answer 5

Task spooler can handle this need. https://vicerveza.homeunix.net/~viric/soft/ts/article_linux_com.html

You can find this tool with the 'tsp' alias in debian and ubuntu .

Answer 6

echo -e "1\n2\n3\n4\n" | xargs -n1 -P4 ./script.sh

Is another way of doing this. xargs is available on basically any system, and control-c should kill all the jobs.

It also (unlike invoking your scripts with &, allows you to run this from a higher-level bash script)

The -n1 option tells xargs to run each argument in it's own process, and the -P4 option tells it to run 4 processes.

Answer 7

I would like to mention an interesting feature of tmux (tmux has already been given as an excellent option by @dan1st). There is a way to run the same command simultaneously in multiple panes. Here is an example. I want to run echo "Fruit name is $fruit" on two different panes/logins/hosts at the same time. Steps:

1. Launch tmux: tmux new-session -s myparallel
2. CTRL-B followed by " (this will split the pane into two. If you want more panes, repeat. " splits horizontally, % splits vertically)
3. Navigate to each pane (using CTRL-B and arrow key) to set the variable for that pane. For example, pane #1 will have fruit="apple" while pane #2 will have fruit="orange"
4. Now that you have the variables set on a pane basis, it is time to synchronize the panes so that whatever you type in one will be mirrored across all panes. The command to do this is CTRL-B :setw synchronize-panes on
5. Now you can run scriptName $fruit and view the output on all panes at the same time.
6. For the sake of completeness, to exit the synchronized mode, type CTRL-B :setw synchronize-panes off

Answer 8

When backgrounding jobs, the shell variable that is printed using: "echo $!" gives the process ID number of the last backgrounded job. You can create a shell script array that holds these process numbers, as you background, and can deal with the processes as you need them. (i.e. you can check to see if they are still running with "ps" or you can kill them.)

Just checked, in bash, the "echo $!" or "shellvar=$!" needs to be on a new line, since ";" does not work after "&".