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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _cmd(self, *nargs):
 """Convenience function for executing a program such as 'git' etc."""

        cmd_str = ' '.join(map(quote, nargs))

        if self.package.config.debug("package_release"):
            print_debug("Running command: %s" % cmd_str)

        p = popen(nargs, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                  cwd=self.pkg_root)
        out, err = p.communicate()

        if p.returncode:
            print_debug("command stdout:")
            print_debug(out)
            print_debug("command stderr:")
            print_debug(err)
            raise ReleaseVCSError("command failed: %s\n%s" % (cmd_str, err))
        out = out.strip()
        if out:
            return [x.rstrip() for x in out.split('\n')]
        else:
            return []