CLI tool to load dot env (.env) file for a program

run-with-dot-env.sh

#!/bin/bash

set -e

# References:
# - Syntax Rules: https://docs.docker.com/compose/env-file/#syntax-rules

function ltrim() {
    # Trim whitespace to the left (leading whitespace)
    local text="$1"
    echo "${text#"${text%%[![:space:]]*}"}"
}

function rtrim() {
    # Trim whitespace to the right (trailing whitespace)
    local text="$1"
    echo "${text%"${text##*[![:space:]]}"}"
}

function parse_and_export_line() {
    # Parse a line of a dot env file

    # Define the first argument of the function
    local line="$1"

    # Trim leading whitespace from line
    line="$(ltrim "$line")"

    if [ -z "$line" ]; then
        # If line is empty,
        # then the line can be ignored.
        return
    fi

    if [ "${line::1}" = "#" ]; then
        # If first character of left-trimmed line is a comment (#),
        # then this is a comment
        return
    fi

    local key
    # Select the first field, delimeted by equals (=)
    key="$(echo "$line" | cut -d '=' -f 1)"
    # Trim trailing whitespace from name
    key="$(rtrim "$key")"

    local value
    # Select all text except for the first field, delimited by equals (=)
    value="$(echo "$line" | cut -d '=' -f 1 --complement)"

    # Export the key-value pair as an environment variable
    eval export "$key='$value'";

}

SCRIPT_NAME="$0"

function usage() {
    echo "USAGE: $SCRIPT_NAME <DOT_ENV_PATH> <PROGRAM>"
    echo "Examples:"
    echo -e "\t$SCRIPT_NAME app.env 'env | grep VARIABLE_IN_DOT_ENV'"
    echo -e "\t$SCRIPT_NAME app.env 'node app'"
}

# Define the first argument of the script
DOT_ENV_PATH="$1"

if [ -z "${DOT_ENV_PATH}" ]; then
    echo 'ERROR: Missing first argument for dot env path!' > /dev/stderr
    usage
    exit 1
fi

# Define the second argument of the script
PROGRAM="$2"

if [ -z "${PROGRAM}" ]; then
    echo 'ERROR: Missing second argument for program!' > /dev/stderr
    usage
    exit 1
fi

# For each line of the input file
while read -r line; do
    # Parse and export each line of the dot env file
    parse_and_export_line "$line"
done < "$DOT_ENV_PATH"

# Now run the program with these environment variables
eval "$PROGRAM"