How do I compare a command output to a text file?

Question

I am learning some programming interview questions so I've coded FizzBuzz. I'm trying to comprare the output of my program to a known good output that's in a .txt file.

How do I check that node fizzbuzz.js output is line by line equal to a expected-output.txt file, or even diff them?

I've tried this as suggested in the duplicate question:

diff -u expected-output.txt <(node fizzbuzz.js)

but diff outputs nothing and never seems to quit until I ^C. The program by itself runs fine, and so does diff -u expected-output.txt <(cat test.txt), it just doesn't seem to play well with node for some reason.

Answer 1

In Bash/ksh/Zsh:

diff -u file.txt <(some command)

The <(some command) construct is called process substitution, and it makes the output from some command available as if from a file, so diff can read it. (It sets up pipes from the command and expands to the name of a named pipe or /dev/fd/N).

Similarly, >(some command) could be used to redirect writes to the command.