iredmail安裝指令碼分析（三）---conf/global DISTRO值的來源及作業系統的判斷

iredmail安裝指令碼分析（三）---conf/global DISTRO值的來源及作業系統的判斷
作者在引入conf/global 檔案時，就已經對作業系統的類型進行判斷，同時也對DISTRO進行了賦值。 部分代碼，顯然檔案裡的KERNEL_NAME的值就是判斷完成的作業系統，具體分析該值是如何得到的。就是通過命令“uname –s  | tr ‘[a-z]’ ‘[A-Z]’得到的，不過作者在此處把小寫換成了大寫。 接下來分析根據不同作業系統，怎麼獲得不同的DISTRO值，代碼如下：

if [ X"${KERNEL_NAME}" == X'LINUX' ]; then    # Directory of RC scripts.    export DIR_RC_SCRIPTS='/etc/init.d'    if [ -f /etc/redhat-release ]; then        # RHEL/CentOS        export DISTRO='RHEL'        # Get distribution version        if grep '\ 6' /etc/redhat-release &>/dev/null; then            # version 6.x            export DISTRO_VERSION='6'        elif grep '\ 7' /etc/redhat-release &>/dev/null; then            # version 7.x            export DISTRO_VERSION='7'        else            export UNSUPPORTED_RELEASE='YES'        fi        # Get distribution name as DISTRO_CODENAME        if grep '^Red' /etc/redhat-release &>/dev/null; then            # RHEL            export DISTRO_CODENAME='rhel'        elif grep '^CentOS' /etc/redhat-release &>/dev/null; then            # CentOS            export DISTRO_CODENAME='centos'        elif grep '^Scientific' /etc/redhat-release &>/dev/null; then            # Scientific Linux            export DISTRO_CODENAME='scientific'        else            export UNSUPPORTED_RELEASE='YES'        fi    elif [ -f /etc/lsb-release ]; then        # Ubuntu        export DISTRO='UBUNTU'        # Ubuntu version number and code name:        #   - 14.04: trusty        #   - 15.04: vivid        export DISTRO_ID="$(grep 'DISTRIB_ID' /etc/lsb-release | awk -F'=' '{print $2}')"        export DISTRO_VERSION="$(grep 'DISTRIB_RELEASE' /etc/lsb-release | awk -F'=' '{print $2}')"        export DISTRO_CODENAME="$(grep 'DISTRIB_CODENAME' /etc/lsb-release | awk -F'=' '{print $2}')"        # Unsupported releases: 12.x, 13.x, 14.10        if echo "${DISTRO_VERSION}" | grep -E '^(12|13|14\.10)' &>/dev/null ; then            export UNSUPPORTED_RELEASE='YES'        fi    elif [ -f /etc/debian_version ]; then        # Debian        export DISTRO='DEBIAN'        # Get major release version number        export DISTRO_VERSION="$(cat /etc/debian_version)"        # Set distro code name and unsupported releases.        if grep '^7' /etc/debian_version &>/dev/null || \            grep -i '^wheezy' /etc/debian_version &>/dev/null; then            export DISTRO_VERSION='7'            export DISTRO_CODENAME='wheezy'        elif grep '^8' /etc/debian_version &>/dev/null || \            grep -i '^jessie' /etc/debian_version &>/dev/null; then            export DISTRO_VERSION='8'            export DISTRO_CODENAME='jessie'        else            export UNSUPPORTED_RELEASE='YES'        fi        # Override settings.        export SHELL_NOLOGIN='/usr/sbin/nologin'    else        export UNSUPPORTED_RELEASE='YES'    fielif [ X"${KERNEL_NAME}" == X'FREEBSD' ]; then    export DISTRO='FREEBSD'    export DISTRO_VERSION="$(uname -r |awk -F'[.-]' '{print $1}')"    # Directory of RC scripts.    export DIR_RC_SCRIPTS='/usr/local/etc/rc.d'    export PYTHON_BIN='/usr/local/bin/python'    # Unsupported releases: 7, 8.    if echo "${DISTRO_VERSION}" | grep '^[78]' &>/dev/null ; then        export UNSUPPORTED_RELEASE='YES'    fi    export SHELL_BASH='/usr/local/bin/bash'    # Default password scheme.    export DEFAULT_PASSWORD_SCHEME='BCRYPT'elif [ X"${KERNEL_NAME}" == X'OPENBSD' ]; then    export DISTRO='OPENBSD'    export DISTRO_VERSION="$(uname -r)"    # Directory of RC scripts.    export DIR_RC_SCRIPTS='/etc/rc.d'    export RC_CONF_LOCAL='/etc/rc.conf.local'    export SHELL_BASH='/usr/local/bin/bash'    export PYTHON_BIN='/usr/local/bin/python'    # Unsupported release: 5.6 and earlier versions.    if echo "${DISTRO_VERSION}" | grep '^5.[123456]' &>/dev/null ; then        export UNSUPPORTED_RELEASE='YES'    fi    # Default password scheme.    export DEFAULT_PASSWORD_SCHEME='BCRYPT'else    # Not support *BSD and other distrobutions yet.    echo "Error: Your OS is not supported yet."    exit 255fi

代碼比較長，不過脈絡比較清晰，首先根據KERNEL_NAME的值判斷是哪種作業系統，作者給出的判斷是3種，分別是LINUX   OPENBSD   FREEBSD  , 也就是該指令碼只能在這3種平台上進行部署，如果需要自己擴充的話，就可以在增加新的判斷，最後如果3種都不是的話，就直接返回255，如下代碼: echo "Error: Your OS is not supported yet."exit 255接下來分析當KERNEL_NAME的值為LINUX，指令碼做了什麼，首先定義了一個變數 export DIR_RC_SCRIPTS='/etc/init.d'linux中一般啟動指令碼都是放在這個目錄裡的,LINUX本身也有很多版本，因此作者在此處又進行多種類型的判斷，判斷的依據檔案分別是/etc/redhat-release  /etc/lsb-release  /etc/debian_version這3種檔案分別對應rhel/centos  ubuntu  debian  , 從而也說明在LINUX的版本中，只支援這3種，其他的LINUX版本是不支援的，最後作者返回一句代碼：定義了一個UNSUPPORTED_RELEASE變數，在後續的代碼應該會調用這個變數來判斷是否支援。 針對這3種LINUX，作者又具體細分到不同的小版本中，首先看rhel/centos 系列，下面代碼： 首先根據存在redhat-release檔案，定義了DISTRO的值 if [ -f /etc/redhat-release ]; thenexport DISTRO='RHEL'這樣在get_all.sh的指令碼裡調用時就有了判斷依據，接著判斷具體的版本， 

if grep '\ 6' /etc/redhat-release &>/dev/null; then            # version 6.x            export DISTRO_VERSION='6'        elif grep '\ 7' /etc/redhat-release &>/dev/null; then            # version 7.x            export DISTRO_VERSION='7'        else            export UNSUPPORTED_RELEASE='YES'        fi

 顯然只支援6和7兩個版本，也就是安裝時，如果不是這2個版本的話，就會返回unsupport_release的值為YES了。 rhel還有兩個個反編譯版本即centos ，Scientific Linux,    因此作者又定義了一個變數來區別 DISTRO_CODENAME, 代碼如下: 

if grep '^Red' /etc/redhat-release &>/dev/null; then            # RHEL            export DISTRO_CODENAME='rhel'        elif grep '^CentOS' /etc/redhat-release &>/dev/null; then            # CentOS            export DISTRO_CODENAME='centos'        elif grep '^Scientific' /etc/redhat-release &>/dev/null; then            # Scientific Linux            export DISTRO_CODENAME='scientific'        else            export UNSUPPORTED_RELEASE='YES'        fi

 顯然在/etc/redhat-release檔案裡，不同的發行版本有不同的關鍵字，這樣關於紅帽系的作業系統，作者就已經區分完畢了。 接下來關於ubuntu的判斷就簡單多了，看圖根據/etc/lsb-release的檔案是否存在，賦值DISTRO為UBUNTU，然後判斷具體版本，看代碼

        export DISTRO_ID="$(grep 'DISTRIB_ID' /etc/lsb-release | awk -F'=' '{print $2}')"        export DISTRO_VERSION="$(grep 'DISTRIB_RELEASE' /etc/lsb-release | awk -F'=' '{print $2}')"        export DISTRO_CODENAME="$(grep 'DISTRIB_CODENAME' /etc/lsb-release | awk -F'=' '{print $2}')"        # Unsupported releases: 12.x, 13.x, 14.10        if echo "${DISTRO_VERSION}" | grep -E '^(12|13|14\.10)' &>/dev/null ; then            export UNSUPPORTED_RELEASE='YES'        fi

 從程式可以看出UBUNTU的ID ,  RELEASE ,  CODENAME的值都在/etc/lsb-release的檔案裡，用grep 和awk匹配後，賦予不同變數的值。 用grep 篩選出系統版本為12,13,14.10的都為不支援版本，目前支援的版本為14.04,15.04 接下來判斷的就是DEBIAN了，同樣是判斷檔案，檔案存在，則DISTRO的值為DEBIAN，接下來判斷版本號碼： # Get major release version number        export DISTRO_VERSION="$(cat /etc/debian_version)"cat /etc/debian_version  一個命令就可以得到具體版本，比rhel更容易判斷 接下來對具體版本進行判斷，見代碼： 

# Set distro code name and unsupported releases.        if grep '^7' /etc/debian_version &>/dev/null || \            grep -i '^wheezy' /etc/debian_version &>/dev/null; then            export DISTRO_VERSION='7'            export DISTRO_CODENAME='wheezy'        elif grep '^8' /etc/debian_version &>/dev/null || \            grep -i '^jessie' /etc/debian_version &>/dev/null; then            export DISTRO_VERSION='8'            export DISTRO_CODENAME='jessie'        else            export UNSUPPORTED_RELEASE='YES'        fi

 

顯然只支援DEBIAN的7,8兩個版本，到此DISTRO的值和作業系統的判斷結束，如果想新增特殊作業系統的話或者自己定義的話，在此處加入自己的代碼即可。