cat exercise

Author: M-Abdoon

implement-shell-tools/cat/cat.js

@@ -0,0 +1,64 @@
+import { program } from "commander";
+import { promises as fs } from "node:fs";
+
+program
+  .name("cat")
+  .description("concatenate and print files")
+  .option("-n, --number", "number all output lines")
+  .option("-b, --number-nonblank", "number nonempty output lines")
+  .argument("<paths...>", "the file paths to process");
+
+program.parse();
+
+const options = program.opts();
+const paths = program.args;
+
+const numberAll = options.number;
+const numberNonBlank = options.numberNonblank;
+
+const shouldNumberAll = numberNonBlank ? false : numberAll;
+
+let lineNumber = 1;
+let nonBlankNumber = 1;
+
+for (const filePath of paths) {
+  try {
+    const content = await fs.readFile(filePath, "utf8");
+    process.stdout.write(formatContent(content));
+  } catch (error) {
+    process.exitCode = 1;
+    process.stderr.write(`cat: ${filePath}: ${error.message}\n`);
+  }
+}
+
+function formatContent(text) {
+  const normalized = text.replace(/\r\n/g, "\n");
+  const endsWithNewline = normalized.endsWith("\n");
+  const lines = endsWithNewline
+    ? normalized.slice(0, -1).split("\n")
+    : normalized.split("\n");
+
+  const output = [];
+
+  for (const line of lines) {
+    if (numberNonBlank) {
+      if (line === "") {
+        output.push("");
+      } else {
+        output.push(`${String(nonBlankNumber++).padStart(6, " ")}\t${line}`);
+      }
+    } else if (shouldNumberAll) {
+      output.push(`${String(lineNumber++).padStart(6, " ")}\t${line}`);
+    } else {
+      output.push(line);
+    }
+  }
+
+  let result = output.join("\n");
+
+  if (endsWithNewline) {
+    result += "\n";
+  }
+
+  return result;
+}