Implement cat command to concatenate files

Author: Droid-An

implement-shell-tools/cat/cat.js

@@ -0,0 +1,60 @@
+import { promises as fs } from "node:fs";
+import { program } from "commander";
+
+program
+  .name("cat")
+  .description("Concatenate and print files")
+  .option("-n", "Number the output lines, starting at 1")
+  .option("-b", "Number the non-blank output lines, starting at 1")
+  .argument("<sample-files...>", "The file path to process")
+  .parse();
+
+const argv = program.args;
+
+const opts = program.opts();
+
+const countLines = (data) => {
+  const lines = data.split("\n");
+  if (lines[lines.length - 1] === "") {
+    lines.pop();
+  }
+
+  let lineNum = 1;
+
+  for (const line of lines) {
+    if (opts.b) {
+      if (line.trim() === "") {
+        console.log();
+      } else {
+        console.log(`${lineNum} ${line}`);
+        lineNum++;
+      }
+    } else if (opts.n) {
+      console.log(`${lineNum} ${line}`);
+      lineNum++;
+    }
+  }
+};
+
+async function example(path) {
+  try {
+    const data = await fs.readFile(path, { encoding: "utf8" });
+    if (opts["b"]) {
+      countLines(data);
+    } else if (opts["n"]) {
+      countLines(data);
+    } else {
+      console.log(data.trimEnd());
+    }
+  } catch (err) {
+    console.error(err);
+  }
+}
+
+const handleInput = async () => {
+  for (const path of argv) {
+    await example(path);
+  }
+};
+
+handleInput();