./gradlew: No such file or direc

gradlew script is so-called Gradle wrapper, a self-contained script which allows people to run Gradle tasks without gradle installed. However it doesn't have to exist to execute Gradle tasks, it's absolutely optional.

You can generate Wrapper in your project by executing the task

gradle wrapper
Afterward, you can use ./gradlew script instead of gradle from PATH

To specify a Gradle version use --gradle-version on the command-line. Just execute the command:

gradle wrapper --gradle-version <your gradle version>
Take a look here for more exhaustive and comprehensive explanation:

参考：https://stackoverflow.com/questions/41407976/gradlew-is-not-found-no-such-file-or-directory