subprocess使用，进入到某个目录下执行shell命令

subprocess是用来fork一个子进程的。这个子进程可以运行一个外部程序。

函数：

• subprocess.call()
• subprocess.check_output()
• subprocess.check_call()

这三个函数都调用Popen函数：因此Popen类的初始化函数的入参，都可以通过被上面三个函数使用

def check_output(*popenargs, **kwargs):
    r"""Run command with arguments and return its output as a byte string.

    If the exit code was non-zero it raises a CalledProcessError.  The
    CalledProcessError object will have the return code in the returncode
    attribute and output in the output attribute.

    The arguments are the same as for the Popen constructor.  Example:

    >>> check_output(["ls", "-l", "/dev/null"])
    'crw-rw-rw- 1 root root 1, 3 Oct 18  2007 /dev/null\n'

    The stdout argument is not allowed as it is used internally.
    To capture standard error in the result, use stderr=STDOUT.

    >>> check_output(["/bin/sh", "-c",
    ...               "ls -l non_existent_file ; exit 0"],
    ...              stderr=STDOUT)
    'ls: non_existent_file: No such file or directory\n'
    """
    if 'stdout' in kwargs:
        raise ValueError('stdout argument not allowed, it will be overridden.')
    process = Popen(stdout=PIPE, *popenargs, **kwargs)

class Popen(object):
    _child_created = False  # Set here since __del__ checks it

    def __init__(self, args, bufsize=0, executable=None,
                 stdin=None, stdout=None, stderr=None,
                 preexec_fn=None, close_fds=False, shell=False,
                 cwd=None, env=None, universal_newlines=False,
                 startupinfo=None, creationflags=0):

举例：app_module_list = subprocess.check_output("grep '\[INFO\] cn.tong' dependency.log | awk '{print $2}' | awk -F':' '{print $2}'", shell=True, cwd=dir)

进入到目录dir后执行shell命令：grep '\[INFO\] cn.tong' dependency.log | awk '{print $2}' | awk -F':' '{print $2}'，标准输出stdout赋值给app_module_list

参考：https://blog.csdn.net/bitcarmanlee/article/details/51622263