add number line flag

Author: pathywang

implement-shell-tools/cat/cat.js

@@ -1,8 +1,19 @@
 const fs = require("fs");
 
-const files = process.argv.slice(2);
+const args = process.argv.slice(2);
 
-for (const file of files) {
-  const content = fs.readFileSync(file, "utf8");
+const numberLines = args[0] === "-n";
+
+const filename = numberLines ? args[1] : args[0];
+
+const content = fs.readFileSync(filename, "utf8");
+
+const lines = content.split("\n");
+
+if (numberLines) {
+  lines.forEach((line, index) => {
+    console.log(`${String(index + 1).padStart(6)}\t${line}`);
+  });
+} else {
   process.stdout.write(content);
 }