12

I'd like to autologin to tty1 on login and then use vlock to lock it.

How can I detect from Bash if the current terminal is a console virtual terminal (e.g. tty1), so that I can put the vlock line into .bash_profile and have it run only if logging in through tty1?

  • 1
    I think you should change the title to "Detect if running in a virtual terminal" because tty can be misunderstood to mean detect if the current shell is connected to a pseudo-terminal device. – Joseph R. Oct 17 '13 at 11:54
  • @JosephR. Thanks for pointing that out, fixed – kiri Oct 17 '13 at 11:58
  • @JosephR: bad call. A pseudo-terminal device is p ty, not tty. About to revert to original title. – Incnis Mrsi Sep 9 '15 at 12:07
  • Related: unix.stackexchange.com/questions/16387/… – Incnis Mrsi Sep 9 '15 at 12:18
13

You can use tty to get the name of the current virtual terminal, then test against it with a case statement:

#!/bin/sh

case $(tty) in /dev/tty[0-9]*)
    vlock ;;
esac
  • Even better, instead of assuming all terminal login shells are ttys. – kiri Oct 17 '13 at 11:38
  • 1
    No need to exclude X: if the script is running in a terminal emulator under X, tty will show the terminal emulator's pseudoterminal, not the physical terminal that X is running on. – Gilles Oct 17 '13 at 21:54
5

It is generally sufficient to simply test STDIN (FD0):

[ -t 0 ] && echo "TTY available" || echo "No TTY available"
  • OK, because .bash_profile is called on login shells and the normal GUI login doesn't have a terminal, so the only terminal login shell should be a tty. Good find – kiri Oct 17 '13 at 11:07
  • 1
    If this snippet were included in a larger script that had its stdin redirected from a file, it would report that no TTY is available even if run from a VT. – Joseph R. Oct 17 '13 at 11:59
  • 1
    @JosephR Correct. The value is often with cron or at jobs to avoid failures when scripts assume interactive input. – JRFerguson Oct 17 '13 at 12:34

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