replaceFirst method
Implementation
void replaceFirst(String text, String replacement) {
final original = readAsStringSync();
final startIndex = original.indexOf(text);
if (startIndex == -1) {
throw "String '$text' not found in ${absolute.path}";
}
final mutated = original.replaceRange(
startIndex,
startIndex + text.length,
replacement,
);
writeAsStringSync(mutated);
}