for j in `cat server_name_list`; do sed -i 's/DIR/${j}/g' dlist1 > $j.conf; done

Basically I am trying to create a number of apache virtual hosts using one virtual host file as a template….

so, template file:
cat /tmp/dlist1

Allow From All
DocumentRoot /var/www/html/DIR
ServerName DIR.com
ServerAlias www.DIR.com
DirectoryIndex index.html index.htm
ErrorLog "logs/DIR_com_error_log"
CustomLog "logs/DIR_com_access_log" common

And the list of servers is in a file

cat /tmp/server_name_list
abc.com
xyz.com
utv.com

so the sed script has to give me three files as in abc.conf, xyz.conf, utv.conf

with this content(just writing the one for "abc" here):

Allow From All
DocumentRoot /var/www/html/abc
ServerName abc.com
ServerAlias www.abc.com
DirectoryIndex index.html index.htm
ErrorLog "logs/abc_com_error_log"
CustomLog "logs/abc_com_access_log" common

>Solution :

Here you go:

for j in `cat server_name_list`; do
  j="${j%.*}"
  sed "s/DIR/$j/g" dlist1 > $j.conf;
done

Explanation:

• j="${j%.*} uses parameter expansion to remove the .com extension from the server name. The syntax ${j%.*} means to remove the shortest match of .* (i.e., ".com") from the end of the string j.
• sed "s/DIR/$j/g" dlist1 > $j.conf replaces all occurrences of the string DIR in the dlist1 template file with the current server name j
• The output of the sed command is redirected to a file with the name $j.conf.

Hope this helps 👍