Pure bash dotenv

dotenv.sh

# This is useful for loading a .env file and ensuring you don't override the
# environment variables already set.
#
# Usage: load-env-file filename.env
load-env-file() {
  local env_file=$1

  # Save a reference of all existing variables
  while IFS= read -rd $'\0' var; do
    name="${var%%=*}"
    [[ "$name" =~ ^[a-zA-Z0-9_]+$ ]] || continue
    local "existing_${name}"=1
  done < <(env -0)

  while IFS= read -rd $'\0' var; do
    # We don't override the environment variables already set
    name="${var%%=*}"
    value="${var#*=}"
    varname="existing_${name}"
    test -n "${!varname}" && continue

    # Then parse each value and export them individually
    eval "$(printf "export %s=%q" "$name" "$value")"
  done < <(env -i -- sh -c "set -ea; . \"$env_file\"; env -0 -u SHLVL -u _ -u PWD")
}