detect_os

#!/bin/bash
#
# Copyright (C) 2023  Keith Valin kvalin@redhat.com
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
#

config="$(dirname $(realpath $0))/configs/detect_os.yml"
os_release=1 # /etc/os-release more reliable, so use it by default
os_release_file="/etc/os-release"
get_version=0 # Fetch OS name by default

usage()
{
    echo -e "detect_os"
    echo -e "\t Detects the OS that the system is currently using and prints it out"
    echo -e "Options"

    echo -e "\t -c/--config"
    echo -e "\t\t The YAML configuration file used to help identify an OS (default is $(dirname $(realpath $0))/configs/detect_os.yml)"

    echo -e "\t --uname"
    echo -e "\t\t Determine the current OS using 'uname -a' output"
    echo -e "\t\t Cannot be combined with --os-release"

    echo -e "\t --os-release"
    echo -e "\t\t Determine the current OS using the /etc/os-release file"
    echo -e "\t\t Cannot be combined with --uname"

    echo -e "\t --os-version"
    echo -e "\t\t Determine the current OS version"
    echo -e "\t\t Works with --uname and --os-release"

    echo -e "\t -h/--help/--usage"
    echo -e "\t\t Displays this message"
}

install_deps()
{
    sys_arch=`arch`
    if [ "$sys_arch" == "x86_64" ]; then
        sys_arch="amd64"
    elif [ "$sys_arch" == "aarch64" ]; then
        sys_arch="arm64"
    fi

    if ! command -v yq > /dev/null 2>&1; then
        if ! command -v wget > /dev/null 2>&1; then
            if command -v yum > /dev/null 2>&1; then
                yum install -y wget
            else
                apt install -y wget
            fi
        fi

        version="v4.35.1"
        bin_name="yq_linux_$sys_arch"
        wget --quiet https://github.com/mikefarah/yq/releases/download/$version/$bin_name -O /usr/bin/yq
        chmod +x /usr/bin/yq
    fi
}

echo_stderr()
{
    echo ${@:1} > /dev/stderr
}

parse_os_release()
{
    if [ ! -f $os_release_file ];then
        echo_stderr Could not find file $os_release_file, aborting
        exit 1
    fi

    local os_id=`grep '^ID=' $os_release_file | cut -d'=' -f2 | sed -e "s/\"\|'//g"`
    local version=`grep '^VERSION_ID=' $os_release_file | cut -d'=' -f2 | sed -e "s/\"\|'//g"`

    local config_len=`yq '. | length' $config`
    for i in `seq 0 $config_len`;do
        local identifier=`yq -r ".[$i].identifier" $config`
        
         if [ $identifier = $os_id ]; then
            if [ $get_version -eq 0 ];then
                echo $identifier
            else
                echo $version
            fi
            exit 0
        fi
    done

    echo_stderr Unknown os \"$os_id\", check $config to make sure it exists
    exit 1
}

parse_uname()
{
    local kinfo=`uname -a`

    local config_len=`yq '. | length' $config`
    for i in `seq 0 $config_len`;do
        local pattern=`yq -r ".[$i].uname_pattern" $config`
        local identifier=`yq -r ".[$i].identifier" $config`
        local ver_pattern=`yq -r ".[$i].uname_version_pattern" $config`

        if [ -z ver_pattern ]; then
            echo $identifier has no uname_version_pattern, skipping
            continue
        fi
        
        local os_match=`echo $kinfo | grep -Eo $pattern`
        
         if [ ! -z $os_match ]; then
            if [ $get_version -eq 1 ];then
                echo $os_match | grep -Eo $ver_pattern
            else
                echo $identifier
            fi
            exit 0
        fi
    done

    echo_stderr No known uname pattern matches, check $config to ensure that a pattern matches the following uname line
    echo_stderr $kinfo
    exit 1
}

NOARG_OPTS=(
    "uname"
    "h"
    "help"
    "os-version"

    "usage"
    "os-release"
)

ARG_OPTS=(
    "c"
    "config"
)

opts=$(getopt \
    --longoptions "$(printf "%s," "${NOARG_OPTS[@]}")" \
    --longoptions "$(printf "%s:," "${ARG_OPTS[@]}")" \
    --name "$(basename "$0")" \
    --options "hc:" \
    -- "$@"
)

if [ $? -ne 0 ]; then
        exit 1
fi

eval set --$opts

flag_set=0

while [[ $# -gt 0 ]]; do
	case "$1" in
    -h | --usage | --help)
        usage
        exit 0
    ;;
    --uname)
        if [ $flag_set -eq 1 ];then
            usage
            exit 1
        fi
        flag_set=1
        os_release=0
        shift 1
    ;;
    --os-release)
        if [ $flag_set -eq 1 ];then
            usage
            exit 1
        fi
        flag_set=1
        os_release=1
        shift 1
    ;;
    --os-version)
        get_version=1
        shift 1
    ;;
    -c | --config)
        config=$2
        shift 2
    ;;
    --)
        break
    ;;
    *)
        echo_stderr Unknown option $1
        exit 1
    ;;
    esac
done

if [ ! -f $config ]; then
    echo_stderr Cannot access $config, aborting
    exit 1
fi

install_deps

if [ $os_release -eq 1 ]; then
    parse_os_release
else
    parse_uname
fi

exit 0