Implement cat with options for line numbering

Author: i786m

implement-shell-tools/cat/cat.mjs

@@ -0,0 +1,49 @@
+import {program} from 'commander';
+import {promises as fs} from 'node:fs';
+import process from 'node:process';
+
+program
+    .name('cat')
+    .description('Concatenates and prints the contents of files.')
+    .argument('<paths...>', 'The paths to the files to concatenate')
+    .option('-n, --number', 'Number all output lines')
+    .option('-b, --number-nonblank', 'Number nonempty output lines');
+
+program.parse();
+
+const argv = program.args;
+const options = program.opts();
+
+if (argv.length < 1) {
+	console.error(
+		`Expected at least 1 argument (a path) to be passed but got ${argv.length}.`,
+	);
+	process.exit(1);
+}
+
+let showLineNumbers = options.number || false;
+let showNonEmptyLineNumbers = options.numberNonblank || false;
+
+if (showLineNumbers && showNonEmptyLineNumbers) {
+    showLineNumbers = false;
+}
+
+let lineNumber = 1;
+const spacer = '    ';
+
+for (const path of argv) {
+    const content = await fs.readFile(path, 'utf-8');
+    const lines = content.split('\n');
+    while (lines.length > 0 && lines[lines.length - 1] === '') {
+        lines.pop();
+    }
+    for (const line of lines) {
+        if (showLineNumbers) {
+            process.stdout.write(`${spacer} ${lineNumber++}  ${line}\n`);
+        } else if (showNonEmptyLineNumbers && line.trim() !== '') {
+            process.stdout.write(`${spacer} ${lineNumber++}  ${line}\n`);
+        } else {
+            process.stdout.write(`${line}\n`);
+        }
+    }
+}

implement-shell-tools/cat/package-lock.json

@@ -1,7 +1,7 @@
 {
-  "name": "prep",
+  "name": "cat",
   "version": "1.0.0",
-  "description": "",
+  "description": "You should already be familiar with the `cat` command line tool.",
   "main": "index.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"