Allows passing of data from the host to a docker container

docker_pipe

#!/bin/bash
#
# A script to facilitate passing data from host to container in a daemon
#
# To read a variable (from within the container):
#       VAR="$(docker_pipe read)"
# 
# !!! Note that reading a variable will block until it is written to !!!
#
# To write to the variable that is being read (from the host):
#       echo "Value" | docker exec -i <CONTAINER_ID> docker_pipe write

: ${FIFO_NAME:=/tmp/docker_pipe}
function cleanup { rm -f "${FIFO_NAME}"; exit ${1}; }
case "${1}" in
    "read")
        trap cleanup SIGHUP SIGINT SIGTERM EXIT
        mkfifo "${FIFO_NAME}" || exit $?
        cat "${FIFO_NAME}" || exit $?
        ;;
    "write")
        [ -p "${FIFO_NAME}" ] || { echo "${FIFO_NAME} does not exist."; exit 1; }
        cat /dev/stdin > "${FIFO_NAME}"
        ;;
    *)
        echo "Usage: ${0} <read|write>" >&2
        exit 1
        ;;
esac