Add script command to allow calling external helper scripts

HELP.md

@@ -129,6 +129,10 @@ Restore a `str` session from a saved state file (default `~/.str.json`).
 #### `runfile <path>`
 Execute the contents of the given file as a series of `str` commands.
 
+#### `script <path> [...<args>]`
+Execute an external script and replace the current subject with the returned output.
+The current subject is passed as the first argument, followed by the optional additional `args`.
+
 
 ### Basic String Operations
 

src/vm/commands/index.ts

@@ -50,6 +50,7 @@ import {Zip} from "./zip.js";
 import {Concat} from "./concat.js";
 import {Call} from "./call.js";
 import {Chunk} from "./chunk.js";
+import {Script} from "./script.js";
 
 export type Commands = Command<CommandData>[]
 export const commands: Commands = [
@@ -90,6 +91,7 @@ export const commands: Commands = [
     new RSub,
     new RunFile,
     new Save,
+    new Script,
     new Set,
     new Show,
     new Sort,

src/vm/commands/script.ts

@@ -0,0 +1,45 @@
+import {Command, ParseContext, processPath, StrTerm, unwrapString, wrapString} from "./command.js";
+import {LexInput} from "../lexer.js";
+import {promisify} from "node:util";
+import {execFile} from "node:child_process";
+import {StrVM} from "../vm.js";
+
+type ScriptData = {
+	path: StrTerm,
+	args: StrTerm[],
+}
+
+export class Script extends Command<ScriptData> {
+	async attemptParse(context: ParseContext): Promise<ScriptData> {
+		const data: ScriptData = {
+			path: await context.popTerm(),
+			args: [],
+		}
+
+		while ( await context.peekTerm() ) {
+			data.args.push(await context.popTerm())
+		}
+
+		return data
+	}
+
+	getDisplayName(): string {
+		return 'script'
+	}
+
+	isParseCandidate(token: LexInput): boolean {
+		return this.isKeyword(token, 'script')
+	}
+
+	async execute(vm: StrVM, data: ScriptData): Promise<StrVM> {
+		return vm.replaceContextMatchingTerm(ctx => ({
+			override: async sub => {
+				const path = processPath(ctx.resolveString(data.path))
+				const args = data.args.map(arg => ctx.resolveString(arg))
+
+				const { stdout, stderr } = await promisify(execFile)(path, [unwrapString(sub), ...args])
+				return wrapString(stdout)
+			},
+		}))
+	}
+}