Search notes:

/etc/os-release

Operating system identification data.
The content of such a file might be: 
NAME="Ubuntu"
VERSION="16.04 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
UBUNTU_CODENAME=xenial
The idea of this file is that it can be «sourced» in a shell which sets the shell variables accordingly: 
$ source /etc/os-release
$ echo "Debian version is $VERSION"
Debian version is 11 (bullseye)

See also

/etc/os-release takes precedence over /usr/lib/os-release.
/etc/*-release files
/etc/debian_version
uname

Links

man os-release

Index

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