Consul watch script to use templates with envsubst

envsubst.consul.sh

#!/bin/bash

# This bash script handles input from Consul Watch (JSON) in order to be able
# to use "envsubst" to fill arbitrary file templates. It handles both single
# as well as multi-object inputs. E.G: JSON strings like "{ object }" or
# "[ {}, {}, array of objects ]".
#
# Usage:
#   - Object JSON from Consul comes from standard input.
#   - You must provide a file template from which ENV substitution will be made.
#   - Consul KEYS are parsed so multi-level keys are parsed and the last
#     slug is used in UPPERCASE for ENV substitution.
#
# Example:
#   $ cat consul.json | ./test.consul.sh /usr/local/config.template
#
#   consul.json: {"Key":"foo/bar/baz", "Value":"TU9BUg==", ...}
#   config.template: baz_value = $BAZ
#

# Create temporary file for setting up environment
TEMP_FILE="$(mktemp -q /tmp/consul.env.XXXXXXXXX)" || exit 1

# Set trap to clean up file
trap 'rm -f -- "$TEMP_FILE"' EXIT
 
jq -rc 'if type=="array" then .[] else . end | [(.Key | split("/") | last | ascii_upcase), (.Value | @base64d)] | "export " + join("=")' > $TEMP_FILE
source "$TEMP_FILE"
envsubst < $1

# Clean up temporary file
rm -f -- "$TEMP_FILE"
# trap - EXIT