You have to recode a small pipe-like program, working like this:
$ mypipe --in fortune --out cowsay _______________________________________
/ Q: What's tiny and yellow and very, \
| very, dangerous? A: A canary with the |
\ super-user password. /
---------------------------------------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
You can use https://clap.rs to parse the command-line arguments, and also follow the guide https://rust-lang-nursery.github.io/cli-wg/