[geuis]

Not sure what cat is supposed to do in this case. All I get is mario.nes: No such file or directory

[mynameisvlad]

.nes is the extension for a NES ROM.

Given you have a NES ROM named “mario.nes” in your current folder, you will play that ROM by executing the full command.

It literally reads the ROM file, what cat normally does.

[teaearlgraycold]

cat is a command that reads one (or more) files from disk and outputs them either to the terminal or to a subsequent command if the pipe | is used.