mrvus
diff --git a/‎src/writeNpmrc.ts‎
Lines changed: 60 additions & 3 deletions b/‎src/writeNpmrc.ts‎
Lines changed: 60 additions & 3 deletions
@@ -4,6 +4,48 @@ import path from "node:path";
 
 import { fallbackLogger, type Logger } from "./shared/cli/logger.js";
 
+export function appendAuthBlockContent({
+	npmrc,
+	existingContent = "",
+	logger = fallbackLogger,
+}: {
+	npmrc: string;
+	existingContent?: string;
+	logger?: Logger;
+}): string {
+	// find our auth token block in the existing content
+	const authTokenPattern = /; begin auth token\n[\s\S]*?\n; end auth token\n?/;
+
+	let newContent: string;
+	if (existingContent && authTokenPattern.test(existingContent)) {
+		logger.info("Found existing auth token block(s), replacing all of them");
+		// using global flag to find all blocks and replace them with a single new block
+		const replacePattern = /; begin auth token\n[\s\S]*?\n; end auth token\n?/g;
+		let replacedFirst = false;
+		newContent = existingContent.replace(replacePattern, () => {
+			if (!replacedFirst) {
+				replacedFirst = true;
+				return npmrc;
+			}
+			// empty string for subsequent matches to remove duplicates
+			return "";
+		});
+	} else {
+		if (existingContent) {
+			logger.info(
+				"No existing auth token block found, appending to existing content",
+			);
+
+			const separator = existingContent.endsWith("\n") ? "" : "\n";
+			newContent = existingContent + separator + npmrc;
+		} else {
+			newContent = npmrc;
+		}
+	}
+
+	return newContent;
+}
+
 export async function writeNpmrc({
 	npmrc,
 	logger = fallbackLogger,
@@ -20,9 +62,24 @@ export async function writeNpmrc({
 	logger.info(`Writing users .npmrc to: ${userNpmrcPath}`);
 
 	try {
-		// Write the content to the .npmrc file
-		// fs.appendFile will create the file if it doesn't exist
-		await fs.appendFile(userNpmrcPath, npmrc, "utf8");
+		let existingContent = "";
+		try {
+			existingContent = await fs.readFile(userNpmrcPath, "utf8");
+		} catch (error) {
+			// gracefully fail, file will be created later
+			if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
+				throw error;
+			}
+		}
+
+		const newContent = appendAuthBlockContent({
+			npmrc,
+			existingContent,
+			logger,
+		});
+
+		// Write the updated content to the .npmrc file
+		await fs.writeFile(userNpmrcPath, newContent, "utf8");
 		logger.info("Successfully wrote .npmrc file");
 	} catch (error) {
 		const errorMessage = `Error writing users .npmrc to ${userNpmrcPath}: ${error instanceof Error ? error.message : ""}`;