feat: working filesystem

src/program/Echo.ts

@@ -0,0 +1,27 @@
+import { Item } from '../fs/Item'
+import type { SimpleStream } from '../utils/SimpleStream'
+import { Program } from './Program'
+
+export class Echo extends Program {
+    constructor() {
+        super()
+    }
+
+    async Exec(_: SimpleStream<string>, stdout: SimpleStream<string>, ___: Item, args: string[]): Promise<number> {
+        let item: Item = await Item.open(args[1])
+
+        if (!(await item.Exists())) {
+            stdout.emit(`echo: error: item ${item.GetPath()} doesn't exist.\n`)
+            return 1
+        }
+
+        if (item.IsDirectory()) {
+            stdout.emit(`echo: error: can't write data to a directory; item ${item.GetPath()} is a directory.\n`)
+            return 2
+        }
+
+        await item.Write(args.slice(2).join(' '))
+
+        return 0
+    }
+}