What is the difference between `process.env.USER` and `process.env.USERNAME` in Node?

Question

This is the most robust documentation I can find for the process.env property: https://nodejs.org/api/process.html#process_process_env.

It mentions USER, but not USERNAME. On my machine (Windows/Bash), when I print the contents of process.env, I see USERNAME (my windows username) but not USER. Similarly, echo $USERNAME shows my name but echo $USER returns nothing.

What is the difference between USER and USERNAME? Is it an operating system thing? Are they interchangeable?

Answer 1

The documentation about process.env that you linked to shows an example environment; it is not meant to be normative. process.env can be basically anything -- its values generally have OS defaults provided by the shell, but ultimately they are controlled by the user and/or the process that launched your process.

ie, a user could run

$ USER=lies node script.js

...and process.env would not contain the real username.

---

If you're interested in getting information about the user your process is running as, call os.userInfo(), which is (mostly¹) consistent across platforms.

> os.userInfo()
{ uid: -1,
  gid: -1,
  username: 'josh',
  homedir: 'C:\\Users\\josh',
  shell: null }

^{1 - on Windows, uid, gid, and shell are useless, as seen above}

os.userInfo() calls uv_os_get_passwd, which returns the actual current effective user, regardless of what's in environment variables.

uv_os_get_passwd Gets a subset of the password file entry for the current effective uid (not the real uid). The populated data includes the username, euid, gid, shell, and home directory. On non-Windows systems, all data comes from getpwuid_r(3). On Windows, uid and gid are set to -1 and have no meaning, and shell is NULL.