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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 call(cmd, timeout=None, signum=signal.SIGKILL, keep_rc=False, encoding="utf-8", env=os.environ):
 """ Execute a cmd or list of commands with an optional timeout in seconds. If `timeout` is supplied and expires, the process is killed with SIGKILL (kill -9) and an exception is raised. Otherwise, the command output is returned. Parameters cmd: str or [[str]] The command(s) to execute timeout: int Seconds before kill is issued to the process signum: int The signal number to issue to the process on timeout keep_rc: bool Whether to return the exit code along with the output encoding: str unicode decoding scheme to use. Default is "utf-8" env: dict The environment in which to execute commands. Default is os.environ Returns ------- str Content of stdout of cmd on success. Raises ------ CalledProcessError Raised when cmd fails """


    if not isinstance(cmd, list):
        cmd = [cmd]

    p = Pipeline(*cmd, timeout=timeout, signum=signum, env=env)
    res = p(keep_rc=keep_rc)

    if keep_rc:
        rc, output = res
        output = output.decode(encoding, 'ignore')
        return rc, output
    return res.decode(encoding, "ignore")