What is the reason for the failure of commonly used commands like "--help" in ADB shell?

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ADB shell is a command-line tool that allows users to communicate with an Android device from a computer. The reason why common commands like "--help" may fail in ADB shell is that ADB shell is not a typical command-line interface. It is designed specifically for communicating with Android devices and has a limited set of commands and functionality. Additionally, some Android manufacturers may have modified the ADB shell to include their own set of commands, further limiting the use of standard commands like "--help". In such cases, users should refer to the device manufacturer's documentation or support resources for specific instructions on using ADB shell.