Making the os_release function more strict

[dmikushin]

Making the os_release CMake function more strict:

1. Adding '=' to match pattern, because on Rocky Linux /etc/os-release contains not only ID="rocky", but also ID_LIKE="rhel centos fedora"
2. Adding '| xargs', because on Rocky Linux ID="rocky" line contains extra quotes

[pmatilai]

Hmm, wouldn't COMMAND sh -c ". /etc/os-release; echo ${var}" achieve the same thing, by letting the shell do the work instead?

[dmnks]

Hmm, wouldn't COMMAND sh -c ". /etc/os-release; echo ${var}" achieve the same thing, by letting the shell do the work instead?

Yep, that's the "canonical" way to use /etc/os-release. For some reason, I didn't realize this when adding this cmake helper.

@dmikushin, feel free to update the PR to just source the file, otherwise I can do that later. Thanks!

[pmatilai]

Heh, yeah sometimes the most obvious answer is just too obvious 😄

[dmnks]

Indeed. It makes one wonder why the file is formatted in a shell-like fashion 😄 Also, I just noticed this is also what man os-release illustrates in the Example 3. Reading os-release in sh(1) section.

[dmnks]

Mentioned above.

[pmatilai]

Merged via #2708 since there's been no activity on this PR. Thanks for the patch + report!