use POSIX compliant command -v instead of which

[miojonka]

Xpra currently depends on the tool which to be installed to find its own binary on a server. The resulting error message is not helpful as it claims the Xpra binary was not found (i.e. Xpra is not installed when it clearly is), but instead it is the binary-to-find-binaries that was not found.

On Archlinux for example which is not installed by default and which in general has different output on different distributions.

Using command -v is POSIX compliant (which is not) and will work on every distribution without requiring to have which installed. It is also the endorsed way to find the path to a binary in $PATH.

This PR should fix this (I only tested it on Archlinux).

[totaam]

Thanks!

[totaam]

This had broken the builds that tried to find nvcc using the now broken which() function.

[chewi]

This has broken the tests. Although I agree that which is bad, command is a shell built-in, so you can't call it with Popen via get_status_output like you're doing here.

[totaam]

@chewi "like you're doing here" - where?

[miojonka]

Like here I guess:

xpra/xpra/os_util.py

Line 871 in 1c335b5

def get_status_output(*args, **kwargs):

For finding the executable maybe shutil.which might be more suited. But it requires Python 3.3 at least.

[chewi]

Yes, I was going to try shutil.which. That's okay, Xpra needs at least Python 3.6 anyway.

[totaam]

And yet another breakage is caused by this change: #3610.