Continuously re-execute a command when it finishes in Bash

Question

I'm trying to figure out a simple way to keep re-executing a command whenever it finishes, for any reason (error or otherwise).

What would be the best way to approach this?

EDIT: I wasn't clear enough before. I need the next execution to wait until the previous one finishes.

EDIT 2: Almost all answers work great. I mistakenly thought most answers would either fork the process or re-execute it just once, neither of which is wanted.

Answer 1

This creates an infinite loop, executing command over and over again.

while :
    do
        command
done

Answer 2

The watch command will repeat a command forever with an interval specified:

watch -n0 <command>

Setting -n to zero effectively puts the interval at nothing (I think it is really .1 seconds).

watch also has the added benefits of aligning the output so visual changes can be seen easily, and has a switch to highlight changes from the last run.

Answer 3

A simple solution would be:

yourcommand; !#

; separates commands, allowing for multiple commands in one line (Bash: Lists)

!# tells bash to "repeat everything I have written so far in this line" (Bash: Event-Designators)

Answer 4

You can plan ahead during command execution (provided it isn't interactive) and enter !! which will execute the previous command again. This works e.g. during ping -c 5.

---

You can also define a function in bash:

function repeat { "$@"; "$@"; }

To persist it, store it in ~/.bashrc.

Then, you can run your command like this:

repeat ping -c5 heise.de

If it's a specific command you want to repeatedly execute (and not e.g. any command), you can replace "$@" in that snippet with your actual command, and name the function e.g. repeat_ping instead.

---

To make it an infinite loop, you can do what @Dennis suggests. I recommend you add a waiting period if you intend to use this in an interactive shell, like this:

function repeat { while 1 ; do "$@" ; sleep 1 ; done; }

Otherwise it's rather inconvenient to abort this infinite loop using Ctrl-Z.