when-up

#!/bin/sh
#
# Wait until a given host is online (determined by ping) then execute the
# given command
#
# Usage:
# ./when-up HOST COMMAND...
#
# Example
# ./when-up 1.2.3.4 ssh 1.2.3.4
#
# Special case:
# when using when-up to ssh to a host, this host does not need to be given twice
# ./when-up ssh 1.2.3.4
#


#
#  Ensure we received the correct number of arguments.
#
if [ $# -lt 2 ]; then
    echo "Usage: when-up HOST COMMAND..."
    exit 1
fi

if [ $1 = "ssh" ]; then
	HOST=$2
else
	HOST=$1
fi

echo "Waiting for $HOST to come online..."

ping -c 1 -W 1 $HOST >/dev/null
while [ $? -ne 0 ]; do
    sleep 1
    ping -c 1 -W 1 $HOST >/dev/null
done

# By the time we reach here the ping-command has completed successfully
# so we can launch the command we were given - along with any arguments.
if [ $1 != "ssh" ]; then
	shift
fi
$*