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https://github.com/schniz/cmd-ts
💻 A type-driven command line argument parser
https://github.com/schniz/cmd-ts
argument-parser hacktoberfest nodejs parse typescript
Last synced: 2 days ago
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💻 A type-driven command line argument parser
- Host: GitHub
- URL: https://github.com/schniz/cmd-ts
- Owner: Schniz
- License: mit
- Created: 2020-02-02T08:39:32.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2024-11-11T17:36:53.000Z (3 days ago)
- Last Synced: 2024-11-11T18:32:19.758Z (3 days ago)
- Topics: argument-parser, hacktoberfest, nodejs, parse, typescript
- Language: TypeScript
- Homepage: https://cmd-ts.now.sh
- Size: 960 KB
- Stars: 241
- Watchers: 5
- Forks: 25
- Open Issues: 49
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
Awesome Lists containing this project
README
# `cmd-ts`
> 💻 A type-driven command line argument parser, with awesome error reporting 🤤
Not all command line arguments are strings, but for some reason, our CLI parsers force us to use strings everywhere. 🤔 `cmd-ts` is a fully-fledged command line argument parser, influenced by Rust's [`clap`](https://github.com/clap-rs/clap) and [`structopt`](https://github.com/TeXitoi/structopt):
🤩 Awesome autocomplete, awesome safeness
🎠Decode your own custom types from strings with logic and context-aware error handling
🌲 Nested subcommands, composable API
### Basic usage
```ts
import { command, run, string, number, positional, option } from 'cmd-ts';
const cmd = command({
name: 'my-command',
description: 'print something to the screen',
version: '1.0.0',
args: {
number: positional({ type: number, displayName: 'num' }),
message: option({
long: 'greeting',
type: string,
}),
},
handler: (args) => {
args.message; // string
args.number; // number
console.log(args);
},
});
run(cmd, process.argv.slice(2));
```
#### `command(arguments)`
Creates a CLI command.
### Decoding custom types from strings
Not all command line arguments are strings. You sometimes want integers, UUIDs, file paths, directories, globs...
> **Note:** this section describes the `ReadStream` type, implemented in `./src/example/test-types.ts`
Let's say we're about to write a `cat` clone. We want to accept a file to read into stdout. A simple example would be something like:
```ts
// my-app.ts
import { command, run, positional, string } from 'cmd-ts';
const app = command({
/// name: ...,
args: {
file: positional({ type: string, displayName: 'file' }),
},
handler: ({ file }) => {
// read the file to the screen
fs.createReadStream(file).pipe(stdout);
},
});
// parse arguments
run(app, process.argv.slice(2));
```
That works okay. But we can do better. In which ways?
- Error handling is out of the command line argument parser context, and in userland, making things less consistent and pretty.
- It shows we lack composability and encapsulation — and we miss a way to distribute shared "command line" behavior.
What if we had a way to get a `Stream` out of the parser, instead of a plain string? This is where `cmd-ts` gets its power from, custom type decoding:
```ts
// ReadStream.ts
import { Type } from 'cmd-ts';
import fs from 'fs';
// Type reads as "A type from `string` to `Stream`"
const ReadStream: Type = {
async from(str) {
if (!fs.existsSync(str)) {
// Here is our error handling!
throw new Error('File not found');
}
return fs.createReadStream(str);
},
};
```
Now we can use (and share) this type and always get a `Stream`, instead of carrying the implementation detail around:
```ts
// my-app.ts
import { command, run, positional } from 'cmd-ts';
const app = command({
// name: ...,
args: {
stream: positional({ type: ReadStream, displayName: 'file' }),
},
handler: ({ stream }) => stream.pipe(process.stdout),
});
// parse arguments
run(app, process.argv.slice(2));
```
Encapsulating runtime behaviour and safe type conversions can help us with awesome user experience:
- We can throw an error when the file is not found
- We can try to parse the string as a URI and check if the protocol is HTTP, if so - make an HTTP request and return the body stream
- We can see if the string is `-`, and when it happens, return `process.stdin` like many Unix applications
And the best thing about it — everything is encapsulated to an easily tested type definition, which can be easily shared and reused. Take a look at [io-ts-types](https://github.com/gcanti/io-ts-types), for instance, which has types like DateFromISOString, NumberFromString and more, which is something we can totally do.
## Inspiration
This project was previously called `clio-ts`, because it was based on `io-ts`. This is no longer the case, because I want to reduce the dependency count and mental overhead. I might have a function to migrate types between the two.