Post History

`watch` will let you do what you want, yes. This can be easily demonstrated by running `watch` with a brief-running command and a delay, such as:

    $ watch -n2 'date; sleep 5'

and observing that the printed time increments in approximately 7-second steps (the two seconds between `watch` executions plus the five seconds sleep inside the command that is being executed). It's only approximately because neither `watch` nor `sleep` are precision tools and you might hit a whole-second boundary, but broadly this will update the time displayed once per seven seconds.

Another way is to run your script inside a loop:

    $ while sleep 7; do date; done

or alternatively

    $ while date; do sleep 7; done

or perhaps more idiomatically

    $ while true; do date; sleep 7; done

(Which one of those to use depends on whether you want a delay before or after the first invocation. The first will `sleep` *first*, then run `date`; the second will do the opposite; the third is explicit about the order of operations. Once running, the observable effect is the same.)

---

Also, if your `check_mail` script can't be allowed to run more than one instance at any one time, *it* should prevent that. An easy way to do so is to use the program `flock` with `-en` (exclusive lock, non-blocking mode) on a relevant file. (An alternative way of expressing `-n` is `-w 0` to specify a zero wait time to acquire the lock if the lock cannot be acquired immediately. See flock(1) for more details.) As an example, if your `check_mail` script ends up calling `fetchmail` naming a configuration file using the latter's `-f`/`--fetchmailrc` parameter, you might do something like:

    fetchmailrc=~/.fetchmailrc.d/some-account.conf
    while true; do
      flock -en $fetchmailrc fetchmail -f $fetchmailrc
      sleep 120
    done

In case the lock cannot be acquired by `flock`, execution will then fall through to the next command more or less immediately instead of `fetchmail` being invoked. The above would attempt again to invoke fetchmail 120 seconds after the previous attempt finishes, whether or not the earlier attempt was successful.