docker-enter

#!/bin/sh

if [ -e $(dirname "$0")/nsenter ]; then
    # with boot2docker, nsenter is not in the PATH but it is in the same folder
    NSENTER=$(dirname "$0")/nsenter
else
    NSENTER=nsenter
fi

if [ -z "$1" ]; then
    echo "Usage: `basename "$0"` CONTAINER [COMMAND [ARG]...]"
    echo ""
    echo "Enters the Docker CONTAINER and executes the specified COMMAND."
    echo "If COMMAND is not specified, runs an interactive shell in CONTAINER."
else
    PID=$(docker inspect --format "{{.State.Pid}}" "$1")
    [ -z "$PID" ] && exit 1
    shift
    COMMAND="$@"

    if [ "$(id -u)" -ne "0" ]; then
        which sudo > /dev/null
        if [ "$?" -eq "0" ]; then
          LAZY_SUDO="sudo "
        else
          echo "Warning: Cannot find sudo; Invoking nsenter as the user $USER." >&2
        fi
    fi
    
    # Get environment variables from the container's root process
    ENV=$($LAZY_SUDO cat /proc/$PID/environ | xargs -0)
    
    # If no command is given, default to `su` which executes the default login shell
    # Otherwise, execute the given command
    [ -z "$COMMAND" ] && COMMAND="su -m root"
    
    # Prepare nsenter flags
    OPTS="--target $PID --mount --uts --ipc --net --pid --"

    # Use env to clear all host environment variables and set then anew
    $LAZY_SUDO "$NSENTER" $OPTS env -i - $ENV $COMMAND
fi