in reply to Why "getlogin" not works in this case?

The behaviour you are seeing is 100% expected and correct. getlogin() is meant to return null if the process is run with no controlling terminal, and that's what you're doing ;)

The getlogin() syscall returns the user associated with the controlling terminal for the process, or null if there is no controlling terminal.

The way you are running perl, via sh -c, with an & to background it, results in the process having no controlling terminal.

You can more simply see this behaviour with the "tty" command, which shows the controlling terminal.

Normally tty returns something like:


But if you run

sh -c "tty &"

You'll see a different output:

not a tty

If you really want to do what you're doing, consider replacing "getlogin()" with "getpwuid($<)" which uses the real user ID rather than the controlling terminal owner, and so works even backgrounded.

  • Comment on Re: Why "getlogin" not works in this case?

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Re^2: Why "getlogin" not works in this case?
by bdimych (Monk) on Jan 22, 2008 at 16:38 UTC
    oops, sorry, many thanks
Re^2: Why "getlogin" not works in this case?
by Anonymous Monk on Mar 26, 2019 at 05:29 UTC

    i see that "getpwuid($<) fail with "Use of uninitialized value $< in concatenation (.) or string at" . It just failed once in 100 times. But i still would like to know when .

    Thanks in advance!