How to Use & in Bash: Run Commands in Background

In bash, placing & at the end of a command runs it in the background, allowing the shell to accept new commands immediately. This is useful for running long tasks without waiting for them to finish.

Syntax

The basic syntax to run a command in the background is:

command &

Here:

• command is any bash command or script you want to run.
• & tells bash to run the command in the background.

bash

sleep 10 &

Output

[1] 12345

Example

This example shows running a sleep command in the background, so the shell is free to accept new commands immediately.

bash

echo "Start"
sleep 5 &
echo "This runs immediately after starting sleep"
wait

Output

Start
This runs immediately after starting sleep

Common Pitfalls

One common mistake is forgetting the &, which causes the shell to wait for the command to finish before accepting new input. Another is running background commands that produce output without redirecting it, which can clutter the terminal.

Example of wrong and right usage:

bash

# Wrong: runs in foreground
sleep 5
echo "Done"

# Right: runs in background
sleep 5 &
echo "Done"

Output

Done

Quick Reference

Tips for using & in bash:

• Use & to run commands without blocking the shell.
• Use jobs to list background jobs.
• Use fg to bring a background job to the foreground.
• Redirect output of background jobs to avoid terminal clutter.

Key Takeaways

Add & after a command to run it in the background in bash.

Background commands let you keep using the shell without waiting.

Use jobs and fg to manage background tasks.

Redirect output of background commands to keep your terminal clean.

Forgetting & runs commands in the foreground, blocking the shell.