Implement 'cat' command alternative with line numbering options

Author: Geraldine-Edwards

implement-shell-tools/cat/cat.js

@@ -0,0 +1,64 @@
+import { program } from "commander";
+import { promises as fs } from "node:fs";
+import process from "node:process";
+
+// configure the CLI program with its name, description, arguments, options, and actions (the help instructions)
+program
+    .name("cat")
+    .description("An alternative to the 'cat' command")
+    .argument("<files...>", "The file(s) to process") 
+    .option("-n, --number", "Number all output lines")
+    .option("-b, --number-nonblank", "Number non-blank output lines")
+    // actions to process the provided files with the specified options (-n, -b)
+    .action(async (files, options) => {
+        try {
+            // call newCat for all files
+            await newCat(files, options.number, options.numberNonblank)
+        } catch (err) {
+        console.error(`Error: ${err.message}`);
+        }
+  });
+
+// parse command-line file arguments using the process.argv array
+program.parse(process.argv);
+
+
+async function newCat(files, numberLines, numberNonBlank) {
+    let lineNumber = 1;
+
+    for (const file of files) {
+        // read each file into a single text string
+        try {
+            const data = await fs.readFile(file, "utf8");
+            // split that string into an array at \n where each element is a line from the file
+            // e.g. lines = ["Line 1", "Line 2", "Line 3"]
+            const lines = data.split("\n")
+
+            // remove trailing blank line caused by a trailing newline
+            if (lines[lines.length - 1] === "") {
+                lines.pop();
+            }
+
+            for (const line of lines) {
+                if (numberNonBlank) {
+                    // check what is left on the line after trimming (truthy = text, falsy = blank)
+                    if (line.trim()) {
+                    console.log(`${lineNumber.toString().padStart(6, ' ')}  ${line}`);
+                    lineNumber++   
+                    }  else {
+                        console.log(line)
+                    } 
+                } else if (numberLines) {
+                    // number all lines
+                    console.log(`${lineNumber.toString().padStart(6, ' ')}  ${line}`);
+                    lineNumber++
+                } else {
+                    // if neither flag print normally
+                    console.log(line)
+                }
+            }
+        } catch (err) {
+              console.error(`Error reading file ${file}: ${err.message}`);
+        }
+    }
+}