Add a --log option to bootstrap-stage

set -eu -o pipefail

declare -r DEFAULT_STAGE=/stage

USAGE="Usage: $0 [--help] [-s STAGE]

USAGE="Usage: $0 [--help] [-s STAGE] [-l LOG]

Prepare the necessary components of an image in a staging directory

  -h|--help         Show this message and exit.

  -s|--stage STAGE  Set the output stage directory. If it does not exist it will

                    be created. (default: $DEFAULT_STAGE)

  -l|--log LOG      Create a symlink at LOG pointing to /dev/stderr

Environment:

  STAGE:  An alternate way of providing --stage

On Logging:

  Some software can only understand logging to a file. Use --log to make

  a symlink pointing to stderr to enable logging output that Docker can handle.

"

export PATH+=:$(dirname $0)

export STAGE=${STAGE-$DEFAULT_STAGE}

declare -a LOGS=()

until [[ $# -eq 0 ]]; do

	case $1 in

		-h|--help) echo "$USAGE"; exit 0 ;;

		-s|--stage) STAGE=$2; shift ;;

		-l|--log) LOGS+=($2); shift ;;

		--*=*) set -- ${1%=*} ${1#--*=} "${@:2}"; continue ;;

		*) echo >&2 "Unknown argument: $1"; exit 2 ;;

	esac

# Run directories

mkdir -p --mode=0755 $STAGE/var/run

test -h $STAGE/run || ln -s /var/run /run

# Log directories

for log in "${LOGS[@]}"; do

	mkdir -p --mode=0755 "$(dirname "$log")"

	ln -s /dev/stderr "$log"

done