Suppose you want to write the same letter to many people except that you want each letter addressed to the senders personally. This can be created using a shell script. Put the names of the recipients (one per line) in a file called names. Create a textfile called template which has the string NAME wherever you want the persons name to appear (e.g., Dear NAME, ...). Finally, write a script that produces one file per name (call each file using the persons name with suffix .txt), containing the personalized letter obtained from the template file (use sed).