Command to refresh output of other command

If I have a command that each time gives me a output, (a status, for example). How I can do it to refresh this output every 2 seconds, for example? I remember that there is one command which can do it.

Example:

cat /proc/mdstat 

[======>..............]  resync = 30.8% (150544832/488383936) finish=65.8开发者_运维问答min speed=85472K/sec

othercommand cat /proc/mdstat

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You're looking for the watch command.

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Example from FrankyFred:

watch -n 5 free -m

will refresh the free -m command every 5s