Command not found: bench in OS X

When doing bench start getting this error. When i made the installation using this link everything was working. I even created a erpnext app and logged in it. But today when i’m running the “bench start” command i’m getting the following error "command not found: bench "

Sorry it is not the problem of frappe. I used “oh my zsh” in my terminal. When i reverted back to bash terminal everything was working fine.