Implement = operator

main.go

@@ -37,8 +37,9 @@ func main() {
 		fmt.Fprintf(os.Stderr, "Example: %s \"<value>(\\d+)</value>,(\\d+)\" \"v1 * 1.5 * v2\" data.xml\n", os.Args[0])
 		fmt.Fprintf(os.Stderr, "   or simplified: %s \"<value>(\\d+)</value>,(\\d+)\" \"v1 * 1.5 * v2\" data.xml\n", os.Args[0])
 		fmt.Fprintf(os.Stderr, "   or even simpler: %s \"<value>(\\d+)</value>\" \"*1.5\" data.xml\n", os.Args[0])
+		fmt.Fprintf(os.Stderr, "   or direct assignment: %s \"<value>(\\d+)</value>\" \"=0\" data.xml\n", os.Args[0])
 		fmt.Fprintf(os.Stderr, "\nNote: v1, v2, etc. are used to refer to capture groups.\n")
-		fmt.Fprintf(os.Stderr, "      If expression starts with an operator like *, /, +, -, etc., v1 is automatically prepended\n")
+		fmt.Fprintf(os.Stderr, "      If expression starts with an operator like *, /, +, -, =, etc., v1 is automatically prepended\n")
 	}
 
 	flag.Parse()
@@ -89,6 +90,10 @@ func buildLuaScript(luaExpr string) string {
 		strings.HasPrefix(luaExpr, "^") || strings.HasPrefix(luaExpr, "%") {
 		luaExpr = "v1" + luaExpr
 		log.Printf("Expression modified to: %s", luaExpr)
+	} else if strings.HasPrefix(luaExpr, "=") {
+		// Handle direct assignment with = operator
+		luaExpr = "v1 " + luaExpr
+		log.Printf("Expression modified to: %s", luaExpr)
 	}
 
 	// Replace shorthand v1, v2, etc. with their direct variable names (no need for array notation)

main_test.go

@@ -303,6 +303,40 @@ func TestLuaMathFunctions(t *testing.T) {
 	}
 }
 
+func TestDirectAssignment(t *testing.T) {
+	fileContents := `
+		<config>
+			<item>
+				<value>100</value>
+			</item>
+		</config>
+	`
+	expected := `
+		<config>
+			<item>
+				<value>0</value>
+			</item>
+		</config>
+	`
+
+	regex := regexp.MustCompile(`(?s)<value>(\d+)</value>`)
+	luaExpr := `=0`
+	luaScript := buildLuaScript(luaExpr)
+
+	t.Logf("Lua script: %s", luaScript) // Log the generated script for debugging
+
+	modifiedContent, err := process(fileContents, regex, luaScript)
+	if err != nil {
+		t.Fatalf("Error processing file: %v", err)
+	}
+
+	normalizedModified := normalizeWhitespace(modifiedContent)
+	normalizedExpected := normalizeWhitespace(expected)
+	if normalizedModified != normalizedExpected {
+		t.Fatalf("Expected modified content to be %q, but got %q", normalizedExpected, normalizedModified)
+	}
+}
+
 // Test with actual files
 func TestProcessingSampleFiles(t *testing.T) {
 	// Read test files