Wait for service to accept connections, using bash /dev/tcp

svcwait.sh

#!/bin/bash

host="127.0.0.1"
port="13337"
maxwait=5

dur=0
while true; do
    ( echo -n "" > /dev/tcp/$host/$port ) 2>/dev/null
    if [[ $? -eq 0 ]]; then
        break
    fi

    if [[ $dur -eq $maxwait ]]; then
        echo "Error: Service $host:$port not ready after max $maxwait seconds"
        exit 1
    fi

    echo "Waiting for service $host:$port to accept connections... ($dur sec)"
    sleep 1
    dur=$((dur+1))
done

echo "Service $host:$port is ready after $dur seconds"

This uses bash's /dev/tcp emulation to wait for a service to accept connections.

This might be useful for a startup/entrypoint script in a Docker image (e.g. wait for a database to be ready).