Fixed Error of Multiple PIDs

[PharrellWANG]

Description of the problem: If the PID output string is 1234\n, i.e., a single PID, the project is able to handle it. But if the PID output string is 1234\n87976\n, i.e., a concatenated string of multiple PIDs, the project cannot handle it. And an error message Enter integer value for port number will jump out.

And this pull request has fixed the bug described above.