CODEWITHSUNDEEP
bashuser-interfaceenvironment-variables
LeonidMew
LeonidMew

Reputation: 502

Bash script - determine if script launched in terminal console or gui

How to find out if script launched using terminal console or without, in gui by .desktop file for example?

I have look over env output and some variables looks promising to check, like test $TERM var. But I want known for sure and a compatible/portable way to do it.

This is needed for script what will have two behaviors for user input, fallback to terminal read or gui input.

Upvotes: 3

Views: 3468

Answers (3)

Anton
Anton

Reputation: 485

The answer by @LeonidMew is incomplete and somewhat incorrect.

You should not detect GUI by presence of STDIN (that's what [ -t 0 ] test does). There are cases when none of STDIN and GUI are available, e.g. when you run the script over ssh session in non-interactive mode. This happens often for CI deploys.

Correct answer heavily depends on your task, in general there are 4 distinct environments:

  1. App is run non-interactively, e.g. from ssh command, spawned as child process without STDIO attached, etc. GUI is missing, STDIN is missing.
  2. App is run interactively from X-session with .desktop file or alike. GUI is present, STDIN is missing.
  3. App is run interactively from linux terminal (ssh, bare text console, hosting recovery console, etc.). GUI is missing, STDIN is present. App can interact with user in text mode via STDIN.
  4. App is run interactively from GUI terminal app, like xterm. GUI is present, STDIN is present.

There are 2 basic tests that can help to identify the environment:

  1. GUI test - whether app can interact with user using graphical windows: test for $DISPLAY env variable.
  2. STDIN test - whether app can interact with user using text console: test for file descriptor 0 (aka STDIN) with if [ -t 0 ]; ...

Combining these two test will give you the environment:

test 1 false + test 2 false: case 1 -- no user interaction available
test 1  true + test 2 false: case 2 -- interact via XWindows
test 1 false + test 2  true: case 3 -- interact via STDIN/console
test 1  true + test 2  true: case 4 -- XWindows or STDIN/console, whichever is preferred

Upvotes: 4

LeonidMew
LeonidMew

Reputation: 502

if [ -t 0 ]; then echo "in a terminal"; fi

That tests file descriptor 0, which is stdin. If you're launching your script as a GUI, that test should be false.

Author: glenn jackman

This won't work if the script is run from a terminal, but with input redirected. – Gordon Davisson

so for the purpose of this discussion, terminal emulator is being conflated with linux console, and both are being distinguished from a "gui method" which I'd thought xterm to be, as it opens in a gui... - JosephHarriott

Purpose of this question was writing script interface usable for text or gui if script run by .desktop shortcut or other gui method.

Upvotes: 3

z atef
z atef

Reputation: 7679

Or: 

 $ [ -t 0 ] &&  echo "in a terminal" || echo "something else"
 in a terminal

Upvotes: 0

Related Questions