A shell script that waits until a command returns successfully.

waitfor

#!/usr/bin/env bash
#
# Usage: waitfor <command>
# Example: waitfor sudo service httpd status
#
# Waits until a command returns true (exit code: 0)
#
# Save or link this file as "waitwhile" to reverse the check,
# and wait while the command returns true.
#

script=`basename $0`

if [ -z $1 ]
then
    echo "Usage: $script <command>"
    echo "Example: $script sudo service httpd status"
    exit 1
fi

if [ $script == "waitwhile" ]
then
    while status=`$*`
    do
        echo $status
        sleep 1
    done
else
    until status=`$*`
    do
        echo $status
        sleep 1
    done
fi

echo $status

I'm using this for a release script, to block until things are ready.

Wait until puppet has finished running:

waitwhile ps -C puppet

Wait until apache is running:

waitfor sudo service httpd status