express command not found in bash after installing it with npm

Starting from express 4.00 you also need to install express generator with:

npm install -g express-generator

Only after this will you be able to run express as a command!

For confirmation see: ExpressJS.com - Migrating to Express 4

npm install express -g

You need to install it globally.

Npm 1.0 installs modules locally by default. So the bash executable lives in /node_modules/bin/. You can add that folder to PATH or you can just install express globally so that it's picked up by PATH