Download and install Sencha Cmd : http://www.sencha.com/products/sencha-cmd/download
Then ensure that the path for Sencha Cmd is in your .bash_profile
:
export PATH=/path/to/Sencha/cmd/3.0.0.250:$PATH
(it will be located in you your 'bin' directory)
Save your .bash_profile
and restart Terminal.
Edit:
You can also try adding the path to your .bashrc
as well. Then restart your terminal and try running sencha
again.
Lastly to verify that Sencha Cmd is in your path do echo $PATH
.