Add util to list frontmatter from all

.eslintrc.json

@@ -16,7 +16,7 @@
   },
   "parserOptions": {
     "ecmaVersion": 2020
-  }, 
+  },
   "overrides": [
     {
       "files": "test/**/*.js",

list-frontmatter.js

@@ -0,0 +1,25 @@
+const argv = require('yargs').command('* [paths..]', 'list frontmatter from files', (yargs) => {
+  return yargs
+    .positional('paths', {
+      describe: 'file paths to list frontmatter from',
+      type: 'array',
+    })
+    .demandOption('paths');
+}).argv;
+
+const frontmatter = require('@github-docs/frontmatter');
+const { readFileSync } = require('fs');
+
+let results = [];
+for (let path of argv.paths) {
+  let markdown = readFileSync(path, 'utf8');
+  const { data, errors } = frontmatter(markdown);
+  if (errors.length) {
+    console.error(JSON.stringify(errors));
+    process.exitCode = 1;
+    return;
+  }
+  results.push({ name: path, ...data });
+}
+
+console.log(JSON.stringify(results, null, 2));

package.json

@@ -26,5 +26,8 @@
     "semver": "^7.3.2",
     "simple-git": "^3.12.0",
     "yargs": "^16.0.3"
+  },
+  "engines": {
+    "node": ">= 12"
   }
 }