dotenv源码解读从.env文件中读取环境变量

const dotenv = require('dotenv')
// 读取.env文件并将其添加到process.env中
dotenv.config()
// 解析一段包含环境变量的字符串或Buffer，返回一个对象
const config1 = dotenv.parse('FOO=bar\nBAR=foo')
console.log(config1) // { FOO: 'bar', BAR: 'foo' }
const buffer = Buffer.from('FOO=bar\nBAR=foo')
const config2 = dotenv.parse(buffer)
console.log(config2) // { FOO: 'bar', BAR: 'foo' }

const fs = require('fs')
const path = require('path')
const os = require('os')
const packageJSON = require('../package.json')
const version = packageJson.version
const LINE = /(?:^|^)\s*(?:export\s+)?([\w.-]+)(?:\s*=\s*?|:\s+?)(\s*'(?:\'|[^'])*'|\s*"(?:\"|[^"])*"|\s*`(?:\`|[^`])*`|[^#\r\n]+)?\s*(?:#.*)?(?:$|$)/mg
// Parser src into an Object
function parse (src) {
  const obj = {}
  // Convert buffer to string
  let lines = src.toString()
  // Convert line breaks to same fORMat
  lines = lines.replace(/\r\n?/mg, '\n')
  let match
  while ((match = LINE.exec(lines)) != null) {
    const key = match[1]
    // Default undefined or null to empty string
    let value = (match[2] || '')
    // Remove whitespace
    value = value.trim()
    // Check if double quoted
    const maybeQuote = value[0]
    // Remove surrounding quotes
    value = value.replace(/^(['"`])([\s\S]*)\1$/mg, '$2')
    // Expand newlines if double quoted
    if (maybeQuote === '"') {
      value = value.replace(/\n/g, '\n')
      value = value.replace(/\r/g, '\r')
    }
    // Add to object
    obj[key] = value
  }
  return obj
}
function _log (message) {
  console.log(`[dotenv@${version}][DEBUG] ${message}`)
}
function _resolveHome (envPath) {
  return envPath[0] === '~' ? path.join(os.homedir(), envPath.slice(1)) : envPath
}
// Populates process.env from .env file
function config (options) {
  let dotenvPath = path.resolve(process.cwd(), '.env')
  let encoding = 'utf8'
  const debug = Boolean(options && options.debug)
  const override = Boolean(options && options.override)
  if (options) {
    if (options.path != null) {
      dotenvPath = _resolveHome(options.path)
    }
    if (options.encoding != null) {
      encoding = options.encoding
    }
  }
  try {
    // Specifying an encoding returns a string instead of a buffer
    const parsed = DotenvModule.parse(fs.readFileSync(dotenvPath, { encoding }))
    Object.keys(parsed).forEach(function (key) {
      if (!Object.prototype.hasOwnProperty.call(process.env, key)) {
        process.env[key] = parsed[key]
      } else {
        if (override === true) {
          process.env[key] = parsed[key]
        }
        if (debug) {
          if (override === true) {
            _log(`"${key}" is already defined in `process.env` and WAS overwritten`)
          } else {
            _log(`"${key}" is already defined in `process.env` and was NOT overwritten`)
          }
        }
      }
    })
    return { parsed }
  } catch (e) {
    if (debug) {
      _log(`Failed to load ${dotenvPath} ${e.message}`)
    }
    return { error: e }
  }
}
const DotenvModule = {
  config,
  parse
}
module.exports.config = DotenvModule.config
module.exports.parse = DotenvModule.parse
module.exports = DotenvModule

function config (options) {
  let dotenvPath = path.resolve(process.cwd(), '.env')
  let encoding = 'utf8'
  const debug = Boolean(options && options.debug)
  const override = Boolean(options && options.override)
}

if (options) {
  if (options.path != null) {
    dotenvPath = _resolveHome(options.path)
  }
  if (options.encoding != null) {
    encoding = options.encoding
  }
}

const parsed = DotenvModule.parse(fs.readFileSync(dotenvPath, { encoding }))

Object.keys(parsed).forEach(function (key) {
    if (!Object.prototype.hasOwnProperty.call(process.env, key)) {
        process.env[key] = parsed[key]
    } else {
        if (override === true) {
            process.env[key] = parsed[key]
        }
        if (debug) {
            if (override === true) {
                _log(`"${key}" is already defined in `process.env` and WAS overwritten`)
            } else {
                _log(`"${key}" is already defined in `process.env` and was NOT overwritten`)
            }
        }
    }
})

const LINE = /(?:^|^)\s*(?:export\s+)?([\w.-]+)(?:\s*=\s*?|:\s+?)(\s*'(?:\'|[^'])*'|\s*"(?:\"|[^"])*"|\s*`(?:\`|[^`])*`|[^#\r\n]+)?\s*(?:#.*)?(?:$|$)/mg
function parse (src) {
  const obj = {}
  // Convert buffer to string
  let lines = src.toString()
  // Convert line breaks to same format
  lines = lines.replace(/\r\n?/mg, '\n')
  let match
  while ((match = LINE.exec(lines)) != null) {
    const key = match[1]
    // Default undefined or null to empty string
    let value = (match[2] || '')
    // Remove whitespace
    value = value.trim()
    // Check if double quoted
    const maybeQuote = value[0]
    // Remove surrounding quotes
    value = value.replace(/^(['"`])([\s\S]*)\1$/mg, '$2')
    // Expand newlines if double quoted
    if (maybeQuote === '"') {
      value = value.replace(/\n/g, '\n')
      value = value.replace(/\r/g, '\r')
    }
    // Add to object
    obj[key] = value
  }
  return obj
}