My node.js application depends on the fact browserify is available on the command line, as it uses it on a shell script. How can I make sure it is available on the application without having to require my client to install it manually via npm install?
Since you're not giving too much context, I'm assuming that your external dependencies are located in ./node_modules in your app's directory.
In that case, just install browserify as an extra (local) dependency, which will make it available as ./node_modules/.bin/browserify. That's also how you can refer to it from your shell script.
An even better option is to install browserify as follows:
npm install --save browserify
This not only installs browserify for you, but also adds it as a dependency to your dependencies in your package.json file.
Now when someone installs your module i.e. via npm install yourmodule, browserify will be installed automatically into its ./node_modules.
This of course works for any module you depend on, not only browserify.