Using Want

This section will get you up and running with Want.

Most of the time you should run want build. This command is suitable to use as a pre-merge check. It will build all the targets in the current module. It does not and can not perform publishing or other side effects.

Creating a Want Module

To start using Want with a new project, first we need to initialize a Module. Change the current working directory to the root of your project source code, and run the following command.

$ want init

You should see a file called WANT in the current directory. This file contains configuration for Want in the Jsonnet configuration language. Jsonnet is used for all the configuration files in Want.

Creating a Build Target

Want calls the things that you, the user want, but don't yet have, and need to build Targets. There are 2 ways to specify targets: as Expressions, and as Statements.

They are each good for different things; in this example we will use an expression.

Create a file myexpr.want anywhere in your project, and fill it with the following

local want = import "@want";

want.blob("Hello World!\n")

Now run

$ want cat myexpr.want
Hello World!

Inspecting the Build Output

Normally cat myexpr.want would print the Jsonnet file above, but instead it printed just the "Hello World!" part. This is because want cat reads from the build output, while the regular cat reads from the regular filesystem, which is the build input.

Want organizes build targets into an output filesystem. This filesystem only exists virtually, within want, but it can be inspected using similar tools to UNIX (ls and cat).

want ls <path> will list the contents of a tree in the build output. Compare this to the output of regular ls.

This simple translation of inputs to outputs is what makes Want so easy to use and reason about. You will never find yourself in a situation where you don't know when/how/where a Target is being computed.

Armed with just want ls, want cat, and want build, you can get pretty far. To learn more about what you can build with Want, read the Build Configuration section.