Take a look at how pacapt detects the OS:
# Detect package type from /etc/issue
_found_arch() {
local _ostype="$1"
shift
grep -qis "$*" /etc/issue && _OSTYPE="$_ostype"
}
# Detect package type
_OSTYPE_detect() {
_found_arch PACMAN "Arch Linux" && return
_found_arch DPKG "Debian GNU/Linux" && return
_found_arch DPKG "Ubuntu" && return
_found_arch YUM "CentOS" && return
_found_arch YUM "Red Hat" && return
_found_arch YUM "Fedora" && return
_found_arch ZYPPER "SUSE" && return
[[ -z "$_OSTYPE" ]] || return
# See also https://github.com/icy/pacapt/pull/22
# Please not that $OSTYPE (which is `linux-gnu` on Linux system)
# is not our $_OSTYPE. The choice is not very good because
# a typo can just break the logic of the program.
if [[ "$OSTYPE" != "darwin"* ]]; then
_error "Can't detect OS type from /etc/issue. Running fallback method."
fi
[[ -x "/usr/bin/pacman" ]] && _OSTYPE="PACMAN" && return
[[ -x "/usr/bin/apt-get" ]] && _OSTYPE="DPKG" && return
[[ -x "/usr/bin/yum" ]] && _OSTYPE="YUM" && return
[[ -x "/opt/local/bin/port" ]] && _OSTYPE="MACPORTS" && return
command -v brew >/dev/null && _OSTYPE="HOMEBREW" && return
[[ -x "/usr/bin/emerge" ]] && _OSTYPE="PORTAGE" && return
[[ -x "/usr/bin/zypper" ]] && _OSTYPE="ZYPPER" && return
if [[ -z "$_OSTYPE" ]]; then
_error "No supported package manager installed on system"
_error "(supported: apt, homebrew, pacman, portage, yum)"
exit 1
fi
}
As you can see it first checks /etc/issue
, then failing that the script looks for the associated executable file for each package manager.
But heck, why not just use pacapt, instead of rolling your own?