Bash piping in OSX prompts command not found, sometimes
This likely happens because you use a keyboard layout with a non-US layout (happened to me too). On German layouts, the pipe is typed with Alt+7, so chances are high that you press Alt+Space afterwards, which will produce a non-breaking space.
A quick solution: Add the line
"\xC2\xA0": " "to your ~/.inputrc (if you are using bash). This will map non-breaking spaces to normal ones which should solve the problem.
If you want more detail (or if you are interested in how you can track down these kinds of issues), I wrote a blog post about it some time ago.