Running (and killing) multiple processes in a single shell script

Something I'm regularly doing during my daily development is running build / server processes.

For example, right now I'm working on a project that requires a Django development web server as well as a sass --watch process to compile CSS. Often I'm also running some node processes like react-native or babel or something.

For me, it's annoying to have 10 terminals open running all of these processes.

I'd rather run it in a single file. A common solution is to use the latest build utility to wire everything up. My opinion is that it's more useful & natural to just call the binaries directly from a bash script.

Here's how you can run multiple processes at once (assuming we have binaries or shell scripts called program_1, program_2, and program_3):

# start the first program and fork it
program_1 &

# store the process ID
program_1_pid=$!

# start the second program and fork it
program_2 &

# store the process ID
program_2_pid=$!

# trap ctrl-c so that we can kill
# the first two programs
trap onexit INT
function onexit() {
  kill -9 $program_1_pid
  kill -9 $program_2_pid
}

# start the third program, don't fork it
program_3

That's it. Name this script something like script.sh and run it using bash script.sh. All three of your programs will run. When you exit (by pressing ctrl+c), first program_3 will quit, then the function onexit will execute, stopping the other two programs.

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That's all for now, hopefully this will help you in your dev life.

Follow me here on dev.to or on Twitter @connorbode for more as I learn & build.

Comments

[Vikas Kumar]

I could not understand the meaning of 'INT' in the trap part of script

[Connor Bode]

I'll explain what I know but I dont have a very deep understanding here (maybe someone else can jump in with more info).

When you hit ctrl-c you send a SIGINT to the script running in your terminal. It's called a "signal" and SIGINT is one of many signals that exist on unix systems.

Think of it like an event that occurs. A "trap" is just an event handler for a signal.

Here's some additional reading on signals: en.m.wikipedia.org/wiki/Signal_(IPC)

[Vikas Kumar]

Thanks, Connor for the explanation but I want to know the specific detail on 'INT'
Is INT and SIGINT the same?

[Connor Bode]

Yes, the INT you see in the script is SIGINT, which is an "interrupt signal"

[Vikas Kumar]

Thanks, Connor it was helpful

[willtemperley]

Thanks! I've found this a much simpler way to run Vite and a bunch of microservices than with Lerna and Turborepo. There seems to be more control over order of execution this way, i.e. start the services before the web app. I also found both build systems prone to leaving zombie processes, it gets boring quickly hunting those down.