ssh-keygen -R saying (wrongly) no matches found
The problem was actually the zsh shell. Given the [xxx.xxx.xx.xxx]:yyyyy syntax, zsh was interpreting the []s as a globbing pattern. That's why I was getting a &quot;zsh: no matches found&quot; error.
In the old Bash shell, this isn't a problem, and the command I gave runs perfectly.
The solution in zsh is to quote the whole hostname, like this:
ssh-keygen -R &quot;[xxx.xxx.xx.xxx]:yyyyy&quot;