If your are getting “bash: clear: command not found” on you first install of cygwin you have to make sure that you include ncurses packages in your cygwin installation. clear.exe doesn´t come in the standard installation. You must include ncurses to get clear.exe in your system. If you are using bash you can use Ctrl-L and get the same result though.
UPDATE: ncurses is a cygwin package in libs category. You can install it using the the Cygwin Setup utility (just run setup.exe again). See screenshot below
