If you’re like me, most of your time writing bash scripts is spent Googling basic things like “how to loop in bash” while grumbling to yourself how easy this would be in a sane language like TypeScript.

As it turns out, you can write shell scripts using TypeScript, and it isn’t even that hard! Here’s how:

1. Install dependencies

If you haven’t already, download and install node.

After node is installed, install both TypeScript and ts-node globally using npm:

npm install typescript ts-node -g

2. Write your shell script in TypeScript

Create a new .ts file with a shebang as its first line that points to ts-node:

#!/usr/bin/env ts-node

Then, add some TypeScript-y stuff:

#!/usr/bin/env ts-node

console.log('Hello from TypeScript!');

3. Make your script runnable

After saving your TypeScript file, you’ll need to update its permissions to allow it to be executed:

chmod u+x your-shell-script.ts

4. Run your TypeScript file

You can now run the script as you would any other command-line utility:

> ./your-shell-script.ts

…which should result in a friendly message in your terminal:

> ./my-shell-script
Hello from TypeScript!

5. Prove to yourself that it’s working

That seemed a bit too easy - shouldn’t there be an intermediate build step in there somewhere? As a sanity check, update your .ts file with something that shouldn’t compile:

#!/usr/bin/env ts-node

console.log('Hello from TypeScript!');

// TypeScript compiler error:
// Type '4' is not assignable to type 'string'.
var myStr: string = 4;

Rerunning your script will now result in something like this:

/Users/nathanfriend/.nvm/versions/node/v7.10.0/lib/node_modules/ts-node/src/index.ts:250
    return new TSError(diagnosticText, diagnosticCodes)
           ^
TSError: ⨯ Unable to compile TypeScript:
test.ts(5,5): error TS2322: Type '4' is not assignable to type 'string'.

    at createTSError (/Users/nathanfriend/.nvm/versions/node/v7.10.0/lib/node_modules/ts-node/src/index.ts:250:12)
    at getOutput (/Users/nathanfriend/.nvm/versions/node/v7.10.0/lib/node_modules/ts-node/src/index.ts:358:40)
    at Object.compile (/Users/nathanfriend/.nvm/versions/node/v7.10.0/lib/node_modules/ts-node/src/index.ts:546:11)
    at Module.m._compile (/Users/nathanfriend/.nvm/versions/node/v7.10.0/lib/node_modules/ts-node/src/index.ts:430:43)
    at Module._extensions..js (module.js:580:10)
    at Object.require.extensions.(anonymous function) [as .ts] (/Users/nathanfriend/.nvm/versions/node/v7.10.0/lib/node_modules/ts-node/src/index.ts:433:12)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Function.Module.runMain (module.js:605:10)

This is good! You shouldn’t be able to run a TypeScript file if it contains compile-time errors.

So where is that compile step?

There isn’t one! Well, not one that you have to explicitly run, anyway. This is the magic of ts-node - it compiles and runs TypeScript files on the fly much like regular node runs JavaScript files.