Dynamically load environment variables after webpack compiles JS using a bash script to replace the values

interpolate_env_into_compiled_js.sh

#!/usr/bin/env bash

## Given env.js that looks something like
#
# const env = {
#    application_env : '~REACT_ENV_REPLACE_JS_APPLICATION_ENV~',
#    };
#    module.exports = env;
# And an environment variable of JS_APPLICATION_ENV=whateverItOughtToBe ... replace any occurrences on runtime (add to docker CMD)
#
####

INPUT_DIRECTORY=$1
APPLICABLE_ENV_VARS=$(printenv | grep "^JS_[a-zA-Z0-9\_+]*")

if [ ! -d ${INPUT_DIRECTORY} ]; then
    echo >&2 "provided input directory not found."
    exit 2
fi

JS_INPUT_FILES=$(ls ${INPUT_DIRECTORY}/ | grep "^.*\.js$");

INVALID_ENV_VAR=0
for CURRENT_ENV_VAR in ${APPLICABLE_ENV_VARS}; do
    CURRENT_ENV_VAR_VALUE=$(echo ${CURRENT_ENV_VAR} | cut -d "=" -f2)
    if [[ ${CURRENT_ENV_VAR_VALUE} =~ [\$|] ]]; then
        echo >&2 "${CURRENT_ENV_VAR} contains a \$ or a | (pipe) character. Please escape it!! No manipulations have occurred."
        INVALID_ENV_VAR=1
    fi
done

if [ ${INVALID_ENV_VAR} -eq 1 ]; then
    exit 2
else
    echo "Environment variable values look safe. Proceeding with manipulating compiled JS."
fi


for CURRENT_ENV_VAR in ${APPLICABLE_ENV_VARS}; do
    CURRENT_ENV_VAR_VALUE=$(echo ${CURRENT_ENV_VAR} | cut -d "=" -f2)

    if [[ ${CURRENT_ENV_VAR_VALUE} =~ [\$|] ]]; then
        echo >&2 "${CURRENT_ENV_VAR} contains a \$ or a | (pipe) character. Please escape it. This environment variable will be skipped,"
        exit 2
    fi

    CURRENT_ENV_VAR_KEY=$(echo ${CURRENT_ENV_VAR} | cut -d "=" -f1)



    SEARCH_PATTERN="~REACT_ENV_REPLACE_${CURRENT_ENV_VAR_KEY}~"
    echo "Searching for: ${SEARCH_PATTERN} and replacing with: ${CURRENT_ENV_VAR_VALUE}"

    for JS_INPUT_FILE in ${JS_INPUT_FILES}; do
        echo "Looking at: ${JS_INPUT_FILE}"
        JS_OUTPUT_FILE="adsf.out"
        COMMAND_TO_EXECUTE="sed -i \"s|${SEARCH_PATTERN}|${CURRENT_ENV_VAR_VALUE}|g\" ${INPUT_DIRECTORY}/${JS_INPUT_FILE}"
        echo ${COMMAND_TO_EXECUTE}
        COMMAND_OUTPUT=$(eval ${COMMAND_TO_EXECUTE})
        echo ${COMMAND_OUTPUT}
    done
done