wait-for-nc

#!/bin/bash
set -eu

if [ $# -lt 1 ]; then
    cat >&2 <<EOM
$(basename "$0") HOST [PORT [SLEEP [TIMEOUT]]]

Wait until netcat to HOST at PORT succeeds.

PORT defaults to 22, on the theory that you're typically running this when
waiting for a server starting up to become SSH-able.
EOM
    exit 1
fi

host="$1"
port="${2-22}"
sleep="${3-10}"
timeout="${4-5}"

set -x
while ! nc -vz -w "$timeout" "$host" "$port"; do
    sleep "$sleep"
done