Fixup handling mismatched braches

src/envsubst.test.ts

@@ -12,10 +12,25 @@ describe("envsubst", () => {
   });
 
   test("unknown variables are replaced by whitespace", () => {
-    expect(envsubst("Home is $XNOPE.")).toEqual(`Home is .`);
+    expect(envsubst("Home is $XNOPE.")).toEqual("Home is .");
   });
 
   test("unknown variables with braces are replaced by whitespace", () => {
-    expect(envsubst("Home is ${XNOPE}.")).toEqual(`Home is .`);
+    expect(envsubst("Home is ${XNOPE}.")).toEqual("Home is .");
+  });
+
+  test("invalid braces are not replaced", () => {
+    expect(envsubst("Home is ${ HOME}.")).toEqual("Home is ${ HOME}.");
+    expect(envsubst("Home is ${HOME }.")).toEqual("Home is ${HOME }.");
+  });
+
+  test("mismatched left brace is not replaced", () => {
+    expect(envsubst("Home is ${HOME.")).toEqual("Home is ${HOME.");
+  });
+
+  test("mismatched right brace is replaced before the brace", () => {
+    expect(envsubst("Home is $HOME}.")).toEqual(
+      `Home is ${process.env.HOME}}.`,
+    );
   });
 });

src/envsubst.ts

@@ -1,10 +1,10 @@
-const REGEXP = new RegExp("\\$\\{?([A-Z_]+)\\}?");
+const REGEXP = new RegExp("\\$([A-Z_]+)|\\$\\{([A-Z_]+)\\}");
+
+function replacer(_match: string, p1: string, p2: string): string {
+  return process.env[p2 ?? p1] ?? "";
+}
 
 /* replace environment variables in an input string, like envsubst(1) */
 export function envsubst(str: string): string {
   return str.replace(REGEXP, replacer);
 }
-
-function replacer(_match: string, k: string): string {
-  return process.env[k] ?? "";
-}