[root@GreetingFiles cprogs]# cat test.txt
s/Proxy_1_ua="[^ ]*"/Proxy_1_ua=192.168.68.42/g
[root@GreetingFiles cprogs]# cat sipura.cfg
Proxy_1_ua=Hello
[root@GreetingFiles cprogs]# sed -f test.txt sipura.cfg > test1.txt
[root@GreetingFiles cprogs]# cat test1.txt
Proxy_1_ua=Hello
[root@GreetingFiles cprogs]#



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my requirement is in test1.txt it should be like 
Proxy_1_ua=192.168.68.42