chore: show help if input does not exist

src/cli.ts

@@ -18,6 +18,19 @@ import { exists } from "@std/fs/exists";
 import { mdToPdf } from "./md-to-pdf.ts";
 import { getFilename } from "./utils/filename.ts";
 
+function printHelp() {
+  const help = `md2pdf: ${
+    green("A simple CLI tool for converting markdown to PDF.")
+  }
+
+${gray("Usage:")} ${green("md2pdf [OPTION]... [FILE]...")}
+
+${yellow("Options:")}
+  ${green("-w, --watch")}    Watch for file changes.
+  ${green("-h, --help")}     Print help.`;
+  console.log(help);
+}
+
 async function generatePdfFromMarkdown(path: string) {
   const pdfName = getFilename(path) + ".pdf";
 
@@ -38,16 +51,7 @@ async function generatePdfFromMarkdown(path: string) {
 const args = await parseArgs(Deno.args);
 
 if (args.h || args.help) {
-  const help = `md2pdf: ${
-    green("A simple CLI tool for converting markdown to PDF.")
-  }
-
-${gray("Usage:")} ${green("md2pdf [OPTION]... [FILE]...")}
-
-${yellow("Options:")}
-  ${green("-w, --watch")}    Watch for file changes.
-  ${green("-h, --help")}     Print help.`;
-  console.log(help);
+  printHelp();
   Deno.exit(0);
 }
 
@@ -73,6 +77,11 @@ if (args._) {
   }
 }
 
+if (paths.length < 1) {
+  printHelp();
+  Deno.exit(0);
+}
+
 await (async () => {
   for (let i = 0; i < paths.length; i++) {
     await generatePdfFromMarkdown(paths[i]);