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Run a Command at Interval, Unintrusively

·2 mins
terminal
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A not so uncommon usecase is needing to run a command repeatedly at fixed intervals, without losing control of your shell. Doing this in the Linux shell is particularly trivial.

I have two quick options for going about this operation:

  1. Use job control to run the command in the background
  2. Use tmux to view the stdout(and/or stderr) of the command by attaching to the session and detaching when you don’t have a need to view the logs.

In these, two cases, I prefer the added option of writing to a log file. This allows me examine what the process has been up to.

Let us pretend we wish to run the date command every 10s

Job Control #

We will pipe stdout and stderr to /dev/null so they don’t get mixed up messages from foreground processes.

watch -n 10 'date | tee -a output.txt' &>/dev/null &

This runs the date command every ten seconds in the background while appending the output to output.txt and swallowing writes to stdout and stderr.

tmux #

If you prefer to view the output of the command interactively, you can use tmux1.

This is my preferred option, as I can attach to the session whenever I want see how things are moving on and detach when done. If you aren’t familiar with tmux, theres at least a billion useful articles online about what it is and how to use it.

The command in this case will not redirect stdout and stderr to /dev/null.

watch -n 10 'date'

  1. Tmux ↩︎