Python之子进程subprocess模块

http://www.cnblogs.com/vamei/archive/2012/09/23/2698014.html

http://blog.csdn.net/jgood/article/details/4498166

http://docs.python.org/library/subprocess

subprocess.call()

[root@typhoeus79 20130925]# more test.py
#!/usr/bin/env python2.7
#-*- coding:utf8 -*-

import subprocess

rc = subprocess.call(["ls","-l"])

print "rc = ",rc
[root@typhoeus79 20130925]# ./test.py
total 4
-rwxr-xr-x 1 root root 118 Sep 25 11:18 test.py
rc =  0

将程序名ls和其对应的参数放在一个list中传给subprocess.call()

通过一个shell来解释字符串

[root@typhoeus79 20130925]# ./sub_shell.py
total 4
-rwxr-xr-x 1 root root 125 Sep 25 11:22 sub_shell.py
rc =  0
[root@typhoeus79 20130925]# more sub_shell.py
#!/usr/bin/env python2.7
#-*- coding:utf8 -*-

import subprocess

rc = subprocess.call("ls -l",shell=True)

print "rc = ",rc

使用shell=True这个参数，使用字符串而不是使用list来运行子进程。python先运行一个shell，然后这个shell来解释整个字符串

Popen

基于Popen()的封装(wrapper)，这些封装的目的在于让我们容易使用子进程。当我们想要更个性化我们的需求的时候，就要转向Popen类，该类生成的对象用来代表子进程

    Using the subprocess module
    ===========================
    This module defines one class called Popen:

    class Popen(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):

[root@typhoeus79 20130925]# ./sub_popen.py
parent process
<subprocess.Popen object at 0x7fed17542050>
[root@typhoeus79 20130925]# PING www.a.shifen.com (220.181.111.148) 56(84) bytes of data.

--- www.a.shifen.com ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4002ms

[root@typhoeus79 20130925]# more sub_popen.py
#!/usr/bin/env python26
#-*- coding:utf8 -*-

import subprocess

child = subprocess.Popen(["ping","-c","","www.baidu.com"])
#child = subprocess.Popen("ping -c5 www.baidu.com",shell=True)

print("parent process")
print child

父进程在开启子进程之后没有等到其完成，而是直接print

改成等待模式：

[root@typhoeus79 20130925]# ./sub_popen.py
PING www.a.shifen.com (220.181.112.143) 56(84) bytes of data.

--- www.a.shifen.com ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4001ms

parent process
<subprocess.Popen object at 0x7fe424c34050>
[root@typhoeus79 20130925]# more sub_popen.py
#!/usr/bin/env python26
#-*- coding:utf8 -*-

import subprocess

child = subprocess.Popen(["ping","-c","","www.baidu.com"])

child.wait()
print("parent process")
print child

父进程中对子进程进行其他操作：

child.poll() #检查子进程状态

child.kill() #终止子进程

child.send_signal() #向子进程发送信号

child.terminate() #终止子进程

子进程的PID存储在child.pid中

子进程的文本流控制

子进程的标准输入、标准输出、标准错误通过如下属性：

{'_child_created': True, 'returncode': 1, 'stdout': None, 'stdin': None, 'pid': 7070, 'stderr': None, 'universal_newlines': False}

child.stdin

child.stdout

child.stderr

可以在Popen()建立子进程的时候改变标准输入、标准输出和标准错误，并可以利用subprocess.PIPE将多个子进程的输入和输出在一起，构成管道pipe:

[root@typhoeus79 20130925]# more sub_pipe.py
#!/usr/bin/env python26
#-*- coding:utf8 -*-

import subprocess

child1 = subprocess.Popen(["ls","-l"],stdout=subprocess.PIPE)

child2 = subprocess.Popen(["wc"],stdin=child1.stdout,stdout=sub
process.PIPE)

out = child2.communicate()

print out
[root@typhoeus79 20130925]# ./sub_pipe.py
('      4      29     167\n', None)

1、child1的stdout将文本输出缓存到subprocess.PIPE中

2、child2的stdin从child1的stdout读取文本

3、child2的输出文本也被存储在subprocess.PIPE中

4、communicate()方法从PIPE中读取相应的文本

communicate是Popen对象的一个方法，该方法会阻塞父进程，直到子进程完成。

    communicate(input=None)
        Interact with process: Send data to stdin.  Read data from stdout
        and stderr, until end-of-file is reached.  Wait for process to
        terminate.  The optional input argument should be a string to be
        sent to the child process, or None, if no data should be sent to
        the child.

        communicate() returns a tuple (stdout, stderr).

        Note: The data read is buffered in memory, so do not use this
        method if the data size is large or unlimited.

可以使用communicate()方法使用PIPE给子进程输入：

#!/usr/bin/env python26
#-*- coding:utf8 -*-

import subprocess
import time

child = subprocess.Popen(["cat"],stdin=subprocess.PIPE)

time.sleep(5)
child.communicate("Hello\n")

通过time.sleep也可以看到communicate是阻塞父进程

对python执行系统命令的封装

def sys_command(system_cmd):
        logger.debug("system_cmd = '%s'." %system_cmd)
        pipe = subprocess.Popen(system_cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True,stdin=subprocess.PIPE)

        stdout, stderr = pipe.communicate()
        returncode = pipe.returncode

        logger.debug("returncode = '%d'." %returncode)
        logger.debug("stdout = '%s'." %stdout)
        logger.debug("stderr = '%s'." %stderr)

        return returncode,stdout,stderr