Shell Programming and Scripting

awk -v s=new_ntpservername '/^server/{$2=s}1' file

sed '/^server .*prefer$/ s/ntpserver_old/new_ntpservername/' file

sed '/^[ ]*server .*prefer[ ]*$/ s/ntpserver_old/new_ntpservername/' file

$ cat -n file
     1  #test
     2  server ntpserver_old prefer
     3  server ntpserver_old prefer

$ awk -v s=new_ntpservername 'NR==2 && /^server/{$2=s}1' file
#test
server new_ntpservername prefer
server ntpserver_old prefer

$ cat server.list
server1
server2

$ cat server.list |xargs -i ssh {} uname -n

while read server
do
  ssh $server perl -i.bak`date +%Y%m%d` -pe 's/ntpserver_old/new_ntpservername/'  /etc/inet/ntp.conf
done < server.list