feat(cat): add CLI flag support for line numbering

- Replace manual argv parsing with commander.js for robust CLI handling
- Add -n/--number flag to number all output lines
- Add -b/--number-nonblank flag to number only non-empty lines
- Refactor variable names for clarity (filePathsToRead, concatenatedContent, etc)
- Improve error handling with process.exitCode = 1
- Remove debug logging

Author: Iswanna

implement-shell-tools/cat/cat.js

@@ -1,19 +1,53 @@
 import process from "node:process";
-import { promises as fs, readFile } from "node:fs";
+import { promises as fs } from "node:fs";
+import { program } from "commander";
 
-const filesToRead = process.argv.slice(2);
-console.log(filesToRead);
+program
+  .option("-n, --number", "number all output lines")
+  .option("-b, --number-nonblank", "number only non-empty lines")
+  .arguments("<files...>")
+  .parse();
 
-async function readMultipleFiles() {
+const cliOptions = program.opts();
+const filePathsToRead = program.args;
+
+async function readAndOutputFiles() {
   try {
-    const results = await Promise.all(
-      filesToRead.map((file) => fs.readFile(file, "utf-8")),
+    const fileContents = await Promise.all(
+      filePathsToRead.map((filePath) => fs.readFile(filePath, "utf-8")),
     );
-    process.stdout.write(results.join(""));
+    const concatenatedContent = fileContents.join("");
+
+    if (cliOptions.number) {
+      // apply -n logic: number all lines
+      const contentLines = concatenatedContent.split("\n");
+      const numberedOutput = contentLines
+        .map((line, index) => {
+          return `${String(index + 1).padStart(6)} ${line}`;
+        })
+        .join("\n");
+      process.stdout.write(numberedOutput);
+    } else if (cliOptions.numberNonblank) {
+      // apply -b logic: number only non-empty lines
+      const contentLines = concatenatedContent.split("\n");
+      let nonblankLineNumber = 0;
+      const numberedOutput = contentLines
+        .map((line) => {
+          if (line.trim() === "") {
+            return line;
+          }
+          nonblankLineNumber++;
+          return `${String(nonblankLineNumber).padStart(6)} ${line}`;
+        })
+        .join("\n");
+      process.stdout.write(numberedOutput);
+    } else {
+      process.stdout.write(concatenatedContent);
+    }
   } catch (err) {
     console.error("Error reading multiple files:", err);
     process.exitCode = 1;
   }
 }
 
-readMultipleFiles();
+readAndOutputFiles();

implement-shell-tools/package-lock.json

@@ -0,0 +1,6 @@
+{
+    "type": "module",
+    "dependencies": {
+        "commander": "^14.0.3"
+    }
+}