How Can I Run Several Bash Commands in Parallel and Wait for Them to Finish?

To set this up, just make sure your commands are organized properly with waits in the right spots. Here’s a basic structure:
```bash
#!/usr/bin/bash

# First Command
php -f getCommands.php

# Parallel Tasks
{ sleep 10; } &
{ sleep 10; }
wait

# Follow-up Command
php -f getSecondSetOfCommands.php

# Final Parallel Tasks
{ sleep 6; }
{ sleep 6; }
wait
``` Make sure your syntax is correct, especially with the grouping for the parallel tasks. Using `wait` after the backgrounds ensures everything finishes as needed!

Why not wrap your commands in a function and then call that function with a `wait` statement inside? It keeps the script organized and gives you better control over the execution flow!

You can actually simplify that a lot using the `wait` command! Just run your first command normally, then start your parallel jobs with an ampersand after them but make sure to include a `wait` before the next command like this:
```bash
php -f getCommands.php
[ -f /tmp/download.txt ] && parallel -j4 --ungroup :::: /tmp/download.txt &
[ -f /tmp/update.txt ] && parallel -j4 --ungroup :::: /tmp/update.txt &
wait
php -f getSecondSetOfCommands.php
[ -f /tmp/download2.txt ] && parallel -j4 --ungroup :::: /tmp/download2.txt &
[ -f /tmp/update2.txt ] && parallel -j4 --ungroup :::: /tmp/update2.txt &
wait
``` This way, it will wait for all those parallel tasks to finish before moving on!

Could `wait` work for your scenario? It’s designed to wait for background processes to finish. You can check more about it in details here: https://unix.stackexchange.com/questions/541311/bash-wait-for-all-subprocesses-of-script

If you just want to combine files, you could consider something like `cat download.txt upload.txt > updown.txt`. It might be easier than running multiple `parallel` commands!