unix: how to cat from 2 inputs?

unix cat

You could do the following (in bash):

(tail -4 file1; tail -4 file2) > file3

This doesn't use cat as per your question but it does achieve the goal you describe.

unix cat

  cat <(tail -4 file1) <(tail -4 file2)

I often use this feature to diff slightly altered versions of two files.

unix cat

You could use pee from moreutils to do this. Here's my solution

pee 'tail file1' 'tail file2' </dev/null > file3

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