added code for the cat file exercises

Author: Luke-Manyamazi

implement-shell-tools/cat/cat.mjs

@@ -0,0 +1,40 @@
+import { readFile, stat } from 'node:fs/promises';
+import { program } from 'commander';
+
+program
+  .name('cat')
+  .description('Prints contents of files')
+  .option('-n, --number-all-lines', 'Number all output lines')
+  .option('-b, --number-non-blank', 'Number non-blank output lines')
+  .argument('<files...>', 'Files to read')
+program.parse();
+
+const { numberAllLines, numNotBlank } = program.opts();
+const files = program.args;
+
+let lineNumber = 1;
+
+for (const file of files) {
+  try {
+    const fileStat = await stat(file);
+    if (fileStat.isDirectory()) {
+      console.error(`cat: ${file}: Is a directory`);
+      continue;
+    }
+    const content = await readFile(file, 'utf-8');
+    const lines = content.split('\n');
+
+    for (const line of lines) {
+      const shouldNumber = (numberAllLines && !numNotBlank) || (numNotBlank && line.trim() !== '');
+
+      if (shouldNumber) {
+        console.log(`${lineNumber.toString().padStart(6)}  ${line}`);
+        lineNumber++;
+      } else {
+        console.log(line);
+      }
+    }
+  } catch (err) {
+    console.error(`cat: ${file}: ${err.message}`);
+  }
+}