为什么“gnome-screensaver-command -q > test.txt”不输出到文件？

Question

In short, I am looking for the explanation why the output of the command does not reach the file. And if I do something wrong here, how do I do it right so the output would reach the file?

The command:

gnome-screensaver-command -q > test.txt

TL;TR

At first, the short story, the point of mine was to find a way for the bash script to tell if someone is working on the computer (the screen is unlocked) or not (the screen is locked). And it seems I have found the command ( gnome-screensaver-command -q ) for that, maybe, not sure yet as I cannot really check the locked/unlocked stages with the script..

If I run the command gnome-screensaver-command -q in the terminal screen itself then I get the output back as expected. The output suggests me I am on the right path with the command:

** Message: 00:06:00.049: Screensaver is not running!

If I run the same code in the script and output the result to the variable IS_SCREEN_LOCKED=$(gnome-screensaver-command -q) then I get nothing back.. I mean, the value of $IS_SCREEN_LOCKED variable is empty.

If I run gnome-screensaver-command -q > test.txt in the terminal then ** Message: 00:06:00.049: Screensaver is not running! reaches the screen and nothing reaches the file... Which tells me the redirect itself works quite ok (because the file is created), just the command is somehow different... May someone explain what's the trick with the output here?

I suspect it is some kind of "different type of stream".. Is there a stream, not sure if that is the good word for it, called "a query" as man states -q - Query the state of the screensaver ?... Not sure what's the matter with the command directing the output to the file here.

System details:

• Ubuntu 20.04.1 LTS (Focal Fossa)
• GNU bash, version 5.0.17(1)-release (x86_64-pc-linux-gnu)
• gnome-screensaver-command 3.6.1

Answer 1

It may be writing to stderr instead of stdout. So redirect fd 2 rather than fd 1.

gnome-screensaver-command -q 2> test.txt