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Repeat a Unix command every x seconds forever


Try the watch command.

Usage: watch [-dhntv] [--differences[=cumulative]] [--help] [--interval=<n>] 
             [--no-title] [--version] <command>`

So that:

watch -n1  command

will run the command every second (well, technically, every one second plus the time it takes for command to run as watch (at least the procps and busybox implementations) just sleeps one second in between two runs of command), forever.

Would you want to pass the command to exec instead of sh -c, use -x option:

watch -n1 -x command

On macOS, you can get watch from Mac Ports:

port install watch

Or you can get it from Homebrew:

brew install watch


while + sleep:

while true
    echo "Hi"
    sleep 1

Here’s the same thing as a shorthand one-liner (From the comments below):

while sleep 1; do echo "Hi"; done

Uses ; to separate commands and uses sleep 1 for the while test since it always returns true. You can put more commands in the loop – just separate them with ;

This is just a shorter version of other while+sleep answers, if you are running this kind of tasks often as your daily routine, using this saves you from unnecessary key presses, and if your command line starts to get longer understanding this one is a bit easier. But this one starts with sleeping first.

This is generally useful if you need to follow something has one-line output like machine load:

while sleep 1; do uptime; done

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