Linux – On what Linux distributions can I rely on the presence of /etc/os-release

Here's what I use to get information about Linux and BSD distributions: http://distrowatch.com/

Go to the Their search, while great, doesn't have a "rolling-release" option. I would suggest searching by the most recent Linux kernel version by selecting "linux" under their package search. The most recent version of any package is shown in parenthesis.

Searching for linux 2.6.36.2 gave the following:

Arch Linux: current

Chakra GNU/Linux: 0.4-alpha2

Gentoo Linux: unstable, stable

Linux From Scratch: unstable

Lunar Linux: moonbase

Mandriva Linux: cooker

Parted Magic: 5.8

PLD Linux Distribution: 3.0

Sorcerer: grimoire

T2 SDE: snapshot

Zenwalk Linux: 7.0-alpha

To get OS and VER, the latest standard seems to be /etc/os-release. Before that, there was lsb_release and /etc/lsb-release. Before that, you had to look for different files for each distribution.

Here's what I'd suggest

if [ -f /etc/os-release ]; then
    # freedesktop.org and systemd
    . /etc/os-release
    OS=$NAME
    VER=$VERSION_ID
elif type lsb_release >/dev/null 2>&1; then
    # linuxbase.org
    OS=$(lsb_release -si)
    VER=$(lsb_release -sr)
elif [ -f /etc/lsb-release ]; then
    # For some versions of Debian/Ubuntu without lsb_release command
    . /etc/lsb-release
    OS=$DISTRIB_ID
    VER=$DISTRIB_RELEASE
elif [ -f /etc/debian_version ]; then
    # Older Debian/Ubuntu/etc.
    OS=Debian
    VER=$(cat /etc/debian_version)
elif [ -f /etc/SuSe-release ]; then
    # Older SuSE/etc.
    ...
elif [ -f /etc/redhat-release ]; then
    # Older Red Hat, CentOS, etc.
    ...
else
    # Fall back to uname, e.g. "Linux <version>", also works for BSD, etc.
    OS=$(uname -s)
    VER=$(uname -r)
fi

I think uname to get ARCH is still the best way. But the example you gave obviously only handles Intel systems. I'd either call it BITS like this:

case $(uname -m) in
x86_64)
    BITS=64
    ;;
i*86)
    BITS=32
    ;;
*)
    BITS=?
    ;;
esac

Or change ARCH to be the more common, yet unambiguous versions: x86 and x64 or similar:

case $(uname -m) in
x86_64)
    ARCH=x64  # or AMD64 or Intel64 or whatever
    ;;
i*86)
    ARCH=x86  # or IA32 or Intel32 or whatever
    ;;
*)
    # leave ARCH as-is
    ;;
esac

but of course that's up to you.