feat(ls): add basic ls CLI with -1 and -a support

- Add ls/ls.js: reads a directory, supports -1 (one-per-line) and -a (include dotfiles)
- Use commander for CLI flags, fs.promises.readdir for reading directories
- Add error handling and set non-zero exit code on failure
- docs(ls): normalize README bullets so example commands render correctly

Author: Iswanna

implement-shell-tools/ls/README.md

@@ -6,9 +6,9 @@ Your task is to implement your own version of `ls`.
 
 It must act the same as `ls` would, if run from the directory containing this README.md file, for the following command lines:
 
-* `ls -1`
-* `ls -1 sample-files`
-* `ls -1 -a sample-files`
+- `ls -1`
+- `ls -1 sample-files`
+- `ls -1 -a sample-files`
 
 Matching any additional behaviours or flags are optional stretch goals.
 

implement-shell-tools/ls/ls.js

@@ -0,0 +1,66 @@
+import process from "node:process";
+import { promises as fs } from "node:fs";
+import { program } from "commander";
+
+program
+  .option("-1, --one-per-line", "list one file per line")
+  .option("-a, --all", "do not ignore entries starting with .")
+  .parse();
+
+const cliOptions = program.opts();
+const cliArguments = program.args;
+
+async function runLsCommand() {
+  try {
+    // determine directory path (use current directory when none provided)
+    let directoryPath;
+    if (cliArguments.length === 0) {
+      directoryPath = ".";
+    } else {
+      directoryPath = cliArguments[0];
+    }
+
+    // read directory entries
+    const directoryEntries = await fs.readdir(directoryPath);
+
+    // filter out dotfiles unless --all was provided
+    const visibleEntries = [];
+    if (cliOptions.all) {
+      for (const name of directoryEntries) {
+        visibleEntries.push(name);
+      }
+    } else {
+      for (const name of directoryEntries) {
+        if (!name.startsWith(".")) {
+          visibleEntries.push(name);
+        }
+      }
+    }
+
+    // build output
+    let outputString = "";
+    if (cliOptions.onePerLine) {
+      for (const name of visibleEntries) {
+        outputString += name + "\n";
+      }
+      // if there are no entries, outputString stays empty
+    } else {
+      for (let i = 0; i < visibleEntries.length; i++) {
+        if (i > 0) {
+          outputString += "  ";
+        }
+        outputString += visibleEntries[i];
+      }
+      if (outputString !== "") {
+        outputString += "\n";
+      }
+    }
+
+    process.stdout.write(outputString);
+  } catch (err) {
+    console.error("Error reading directory:", err);
+    process.exitCode = 1;
+  }
+}
+
+runLsCommand();