frontend/node_modules/cross-env/src/variable.js

const isWindows = require('./is-windows')

const pathLikeEnvVarWhitelist = new Set(['PATH', 'NODE_PATH'])

module.exports = varValueConvert

/**
 * This will transform UNIX-style list values to Windows-style.
 * For example, the value of the $PATH variable "/usr/bin:/usr/local/bin:."
 * will become "/usr/bin;/usr/local/bin;." on Windows.
 * @param {String} varValue Original value of the env variable
 * @param {String} varName Original name of the env variable
 * @returns {String} Converted value
 */
function replaceListDelimiters(varValue, varName = '') {
  const targetSeparator = isWindows() ? ';' : ':'
  if (!pathLikeEnvVarWhitelist.has(varName)) {
    return varValue
  }

  return varValue.replace(/(\\*):/g, (match, backslashes) => {
    if (backslashes.length % 2) {
      // Odd number of backslashes preceding it means it's escaped,
      // remove 1 backslash and return the rest as-is
      return match.substr(1)
    }
    return backslashes + targetSeparator
  })
}

/**
 * This will attempt to resolve the value of any env variables that are inside
 * this string. For example, it will transform this:
 * cross-env FOO=$NODE_ENV BAR=\\$NODE_ENV echo $FOO $BAR
 * Into this:
 * FOO=development BAR=$NODE_ENV echo $FOO
 * (Or whatever value the variable NODE_ENV has)
 * Note that this function is only called with the right-side portion of the
 * env var assignment, so in that example, this function would transform
 * the string "$NODE_ENV" into "development"
 * @param {String} varValue Original value of the env variable
 * @returns {String} Converted value
 */
function resolveEnvVars(varValue) {
  const envUnixRegex = /(\\*)(\$(\w+)|\${(\w+)})/g // $my_var or ${my_var} or \$my_var
  return varValue.replace(
    envUnixRegex,
    (_, escapeChars, varNameWithDollarSign, varName, altVarName) => {
      // do not replace things preceded by a odd number of \
      if (escapeChars.length % 2 === 1) {
        return varNameWithDollarSign
      }
      return (
        escapeChars.substr(0, escapeChars.length / 2) +
        (process.env[varName || altVarName] || '')
      )
    },
  )
}

/**
 * Converts an environment variable value to be appropriate for the current OS.
 * @param {String} originalValue Original value of the env variable
 * @param {String} originalName Original name of the env variable
 * @returns {String} Converted value
 */
function varValueConvert(originalValue, originalName) {
  return resolveEnvVars(replaceListDelimiters(originalValue, originalName))
}