Putting these all together, you'll probably want a command like:
add adehnert # If on an Athena machine, to make the script available
-mail-merge asa-admin@mit.edu missing-whatever.txt missing-whatever.test.csv # repeat until the message looks good
-mail-merge asa-admin@mit.edu missing-whatever.txt missing-whatever.csv # run just once
+cd /mit/adehnert/Public/software/my-snippets/mail-merge-help # change to the directory with your data files
+mail-merge asa-admin@mit.edu missing-whatever.txt missing-whatever.test.csv # repeat until the message looks good
+mail-merge asa-admin@mit.edu missing-whatever.txt missing-whatever.csv # run just once
The script will output the rows in the CSV file, as it parsed them, as it reads and processes them.