Reputation: 9213

How do I run multiple background commands in bash in a single line?

I normally run multiple commands with something like this:

sleep 2 && sleep 3

sleep 2 ; sleep 3

but what if I want to run them both in the background from one command line command?

sleep 2 & && sleep 3 &

doesn't work. And neither does replacing && with ;

Is there a way to do it?

Upvotes: 308

Answers (7)

Bemipefe

Reputation: 1537

You can use the bash command substitution $(command) like this:

$(command1 ; command2) &

Note that stdin and stdout are still linked to the parent process and redirecting at least the stdout can be tricky. So alternatively you can chain the commands in a single line then pass the string to the bash command to spawn a new process which will handle the execution.

bash -c "command1 ; command2" &

This is especially useful in a bash script when you need to run multiple commands in background.

These two statements should be equivalent. A bash process is spawn in both cases to handle the command (chain of commands) and the & at the end detaches the execution.

This time you can add &>/dev/null before the & at the end of the command to redirect at least the stdout and avoid the output on the stdout of the parent process. Something like:

bash -c "command1 ; command2" &>/dev/null &

Upvotes: 4

Kitsune

Reputation: 9341

Exactly how do you want them to run? If you want them to be started in the background and run sequentially, you would do something like this:

{ sleep 2; sleep 3; } &

If you want sleep 3 to run only if sleep 2 succeeds, then:

sleep 2 && sleep 3 &

If, on the other hand, you would like them to run in parallel in the background, you can instead do this:

sleep 2 & sleep 3 &

And the two techniques could be combined, such as:

{ sleep 2; echo first finished; } & { sleep 3; echo second finished; } &

Bash being bash, there's often a multitude of different techniques to accomplish the same task, although sometimes with subtle differences between them.

Upvotes: 542

dingyang wang

Reputation: 11

I have the same mission too. I have try (sleep2 ; fg )& sleep3 ; fg,it's working. And when you preass ctrl+c doubled,the two process can be stoppped.

Upvotes: 1

Greg Reagle

Reputation: 71

The answers above use parentheses. Bash also can use braces for a similar purpose:

{ sleep 2 && sleep 3; } &

Note that the braces are more picky about syntax--the space after {, the space before }, and the final semicolon are required. In some situations the braces are more efficient because they don't fork a new subshell. In this case I don't know if it makes a difference.

Upvotes: 7