Hi,
sorry, i can't find the difference between the two lines of commands you provided.
this command is make the yum to exclude these program if $isExc is empty.
142 path=/etc/yum.conf
143 isExc=`cat $path|grep httpd`
144 if [ "$isExc" = "" ];then
145 echo "exclude=httpd nginx php mysql mairadb python-psutil python2-psutil" >> $path
146 fi