Apply environment variables to a plain text file that has been prepared as a configuration template

dockify-config-file.sh

#!/usr/bin/env bash

# Usage: dockify-config-file.sh PREFIX INFILE OUTFILE
#
# Will lockup environment variables that start with PREFIX_
# and replace all occurences of ${PREFIX_...} in INFILE,
# writing to OUTFILE.
#
# Useful for converting a non-docker friendly configuration file into
# a template which can be populated at runtime.

PREFIX="$1"
INFILE="$2"
TEMPFILE="${INFILE}.tmp"
OUTFILE="$3"

KEY_VALUE_PAIRS=`env | egrep "^${PREFIX}_"`

cp "${INFILE}" "${TEMPFILE}"

for PAIR in $KEY_VALUE_PAIRS
do
	KEY_VALUE=(${PAIR//=/ })
	KEY=${KEY_VALUE[0]}
	VAL=${KEY_VALUE[1]}

	REPLACE=s/'${'${KEY}'}'/${VAL}/g

	sed -i "''" "${REPLACE}" "${TEMPFILE}"
done

mv "${TEMPFILE}" "${OUTFILE}"
echo Wrote to ${OUTFILE}