Prints the start of a note without leaving the shell. Long notes are cut short, and the link underneath opens the whole thing. The .md is optional.

A note you have appended to or replaced shows your part in full and in the colour of things that are only here — being the part you came to look at — and says so underneath. Through a pipe it is the text and nothing else: cat note | tail -2 is the last two lines of the note.

A file you may not read says Permission denied and names nothing of what is in it, which is the whole of what a mode is for.

cat is also the only way to read the machine’s own files — /etc/passwd, ~/.zshrc, the manual’s source under /usr/share/man — since none of those has a page. What you made yourself does have one: see man open.