Shell Programming and Scripting

read var
if [ -z $var ]
then
 var=your value
fi

$ ./s
do u need this server[dingdong.xxx.com]:
server is: dingdong.xxx.com
$ ./s
do u need this server[dingdong.xxx.com]: another
server is: another
$ cat s
#! /bin/bash

read -p  "do u need this server[dingdong.xxx.com]: " server
printf "server is: ${server:=dingdong.xxx.com}\n"

man bash|less -p:=

     ${parameter:=word}    Assign Default Values.  If parameter is unset or
                           null, the expansion of word is assigned to parame‐
                           ter.  In all cases, the final value of parameter is
                           substituted.  Only variables, not positional param‐
                           eters or special parameters, can be assigned in
                           this way.