feat: build custom cat CLI using commander with file reading, line numbering and wildcard expansion

Author: RahwaZeslusHaile

implement-shell-tools/cat/sample-files/myCat.js

@@ -0,0 +1,72 @@
+#!/usr/bin/env node
+const { program } = require("commander");
+const fs = require("fs");
+const path = require("path");
+
+function expandWildcard(pattern) {
+  const dir = path.dirname(pattern);
+  const base = path.basename(pattern);
+
+  if (!base.includes("*")) return [pattern];
+
+  let files;
+  try {
+    files = fs.readdirSync(dir);
+  } catch (e) {
+    console.error(`cat: ${pattern}: No such directory`);
+    return [];
+  }
+
+  const regex = new RegExp("^" + base.replace(/\*/g, ".*") + "$");
+
+  return files
+    .filter((f) => regex.test(f))
+    .map((f) => path.join(dir, f));
+}
+
+function printFile(filename, options) {
+  let text;
+  try {
+    text = fs.readFileSync(filename, "utf-8");
+  } catch {
+    console.error(`cat: ${filename}: No such file`);
+    return;
+  }
+
+  const lines = text.split("\n");
+  let counter = 1;
+
+  lines.forEach((line) => {
+    if (options.numberAll) {
+      console.log(`${counter} ${line}`);
+      counter++;
+    } else if (options.numberNonEmpty) {
+      if (line.trim() === "") {
+        console.log(line);
+      } else {
+        console.log(`${counter} ${line}`);
+        counter++;
+      }
+    } else {
+      console.log(line);
+    }
+  });
+}
+
+program
+  .name("mycat")
+  .description("A custom implementation of the cat command")
+  .argument("<files...>", "files or wildcard patterns")
+  .option("-n, --number-all", "number all lines")
+  .option("-b, --number-nonempty", "number non-empty lines")
+  .action((patterns, options) => {
+    let allFiles = [];
+
+    patterns.forEach((p) => {
+      allFiles = allFiles.concat(expandWildcard(p));
+    });
+
+    allFiles.forEach((file) => printFile(file, options));
+  });
+
+program.parse();