Jenkins swarm slave docker entrypoint script

swarm.sh

#!/usr/bin/env bash
set -e

# checks and defaults
SWARM_JAR="$JENKINS_HOME"/swarm-client-"$SWARM_VERSION".jar

[ -z "$SWARM_MASTER" ] && echo "SWARM_MASTER was not specified, enabling autodiscovery"
[ -z "$SWARM_NAME" ] && SWARM_NAME="$HOSTNAME"
[ -z "$SWARM_DESCRIPTION" ] && SWARM_DESCRIPTION="Swarm version: $SWARM_VERSION - Jenkins slave for docker jobs"

[ -z "$SWARM_CREDENTIALS_FILE" ] && SWARM_CREDENTIALS_FILE="/etc/jenkins-master/credentials"
[ -f "$SWARM_CREDENTIALS_FILE" ] && SWARM_USERNAME=$(head -n1 $SWARM_CREDENTIALS_FILE) \
                                    SWARM_PASSWORD=$(tail -n1 $SWARM_CREDENTIALS_FILE)
                                          
DOCKER_CONFIG_FILE="${HOME}/.docker/config.json"
DOCKER_CONFIG_DIRECTORY=$(dirname "$DOCKER_CONFIG_FILE")
DOCKER_REPOSITORY=${DOCKER_REPOSITORY:-'https://index.docker.io/v1/'}
DOCKER_REPOSITORY_USERNAME=${DOCKER_REPOSITORY_USERNAME}
DOCKER_REPOSITORY_PASSWORD=${DOCKER_REPOSITORY_PASSWORD}

[ -d "$DOCKER_CONFIG_DIRECTORY" ] || mkdir "$DOCKER_CONFIG_DIRECTORY"
if [ ! -f "$DOCKER_CONFIG_FILE" ] && [ ! -z "$DOCKER_REPOSITORY_USERNAME" ] && [ ! -z "$DOCKER_REPOSITORY_PASSWORD" ]; then
    # if the config file does not exist and
    # the username and password variables are defined
    # create the config file for a single docker repository
    # for multiple docker repositories, supply a file at this location
    cat > ${DOCKER_CONFIG_FILE} <<- EOF
{
    "auths": {
        "${DOCKER_REPOSITORY}": {
            "auth": "$(echo -n ${DOCKER_REPOSITORY_USERNAME}:${DOCKER_REPOSITORY_PASSWORD} | base64 -w 0)"
        }
    }
}
EOF
fi

# entrypoint
exec java -jar "$SWARM_JAR" \
          -fsroot "$JENKINS_HOME" \
          -noRetryAfterConnected \
          -showHostName \
          $([ -n "$SWARM_MASTER" ] && echo "-master ${SWARM_MASTER}" )\
          -name "$SWARM_NAME" \
          -description "${SWARM_DESCRIPTION}" \
          -executors "${SWARM_EXECUTORS:-1}" \
          -mode "${SWARM_MODE:-exclusive}" \
          -labels "${SWARM_LABELS:-docker}" \
          -retry "${SWARM_RETRY:-10}" \
          -username "${SWARM_USERNAME:-admin}" \
          -password "${SWARM_PASSWORD:-passwerd}" \
          "$@"