Ubuntu – Repeat terminal command until specified output

bashcommand linedropbox

I would like to define an alias that performs a command every x seconds until an underlying process gives a designated output. Then, the command should stop being run.

Is this possible, and if so, how?
Help is much appreciated.

I'm almost satisfied with

alias test1='while true; do <command>; sleep 1; done'

except I have to manually stop it, and can therefore not make it execute a new command once finished.

The reason for the question:
Dropbox synchronizes poorly at work. Sometimes, I have to restart it. I would like to do that using a command which also tells when the sync is done, e.g. by

alias drop='dropbox stop && dropbox start && while true; do dropbox status; sleep 1; done'

I would like the repetition stopped when Dropbox outputs 'Up to date'.

Best Answer

Set a condition for the while loop

If you replace

while true

by:

while [ "$(dropbox status)" != "Up to date" ]

it works as you describe.

The command

To stop/start Dropbox and finish after synchronizing is done becomes then:

dropbox stop && dropbox start && while  [ "$(dropbox status)" != "Up to date" ]; do dropbox status; sleep 1; done

Or better (to prevent doubling dropbox status):

dropbox stop && dropbox start && while  [ "$(dropbox status)" != "Up to date" ]; do echo "Updating"; sleep 1 ; done && echo "Finished"

Explanation

while true is waiting for a break condition inside the loop (which never comes), but while [ "$(dropbox status)" != "Up to date" makes the loop break if dropbox status returns Up to date