By default, the comm command separates $($delimits$)$ the output columns with a tab. To change the delimiter

from a tab to another character, use the $--$output$-$delimiter option. For example, to separate columns using the

plus sign use the following command.

comm $--$nocheck$-$order $--$output$-$delimiter$=+$ avengers.txt avengers$2.$txt

Compare the $2$ avengers files separating each column with commas $(,).$