check_env(){    # Check user PRivilege.    #檢查用戶權限

    check_user root    # Check FQDN hostname.

    #檢查主機名是否符合規則    check_hostname    # Check config tool: dialog.

    #檢查配置工具dialog是否存在    check_pkg ${BIN_DIALOG} ${PKG_DIALOG}    ECHO_INFO -n "Checking configuration file: ${IREDMAIL_CONFIG_FILE} ..."    #判斷配置文件是否存在，默認的安裝包下是沒有的，應該是用于安裝中斷后，恢復安裝的。

    if [ -f ${IREDMAIL_CONFIG_FILE} ]; then        if grep '^#EOF$' ${IREDMAIL_CONFIG_FILE} >/dev/null; then            echo -e " [FOUND]"            ECHO_QUESTION -n "Use it for mail server setting? [y|N]"

                        #讀取已經存在的配置文件

            read_setting ${AUTO_USE_EXISTING_CONFIG_FILE}

            #給用戶一個選擇，是用已經存在的配置文件，還是重新安裝

            case $ANSWER in                Y|y )                    ECHO_INFO "Use config file: ${IREDMAIL_CONFIG_FILE} for mail server setting."                    . ${IREDMAIL_CONFIG_FILE}                    # Check installation status.                    # After each component installation was completed, there                    # should be a variable in ${STATUS_FILE}, e.g.                    #                    #   export STATUS_php_INSTALLATION='DONE'                    #   export STATUS_PHP_CONFIGURATION='DONE'                    #

                    #判斷狀態文件是否存在，如果存在則讀取狀態文件

                                    if [ -f ${STATUS_FILE} ]; then                        ECHO_INFO "Import installation process status from file: ${STATUS_FILE}."                        . ${STATUS_FILE}                    else                        echo '' > ${STATUS_FILE}                    fi                    # Initialize tip file.

                    #tip文件是安裝完成后的一些賬號密碼文件，此處初始化該文件

                                  if [ ! -f ${TIP_FILE} ]; then                        cat > ${TIP_FILE} <<EOF${CONF_MSG}EOF                    fi                    ;;                N|n|* )                    ECHO_INFO "Skip configuration file: ${IREDMAIL_CONFIG_FILE}."

                    #新的安裝，CONFIG_VIA_DIALOG在conf/global中定義，他的值是

                                   #export CONFIG_VIA_DIALOG="${DIALOG_DIR}/config_via_dialog.sh"  執行窗口安裝程序，開始新的安裝                    . ${CONFIG_VIA_DIALOG}                    ;;            esac        else            ECHO_INFO "Found, but not finished."            . ${CONFIG_VIA_DIALOG}        fi    else        ECHO_INFO "[NOT FOUND]"        . ${CONFIG_VIA_DIALOG}    fi    check_runtime_dir}