subprocess

如果想在系统上执行命令, 应该用subprocess模块

subprocess模块允许你产生新的子进程，连接到input/output/error管道，并且获得它们的返回码(值).  这个模块用来替换下面旧的模块和函数

• os.system(),
• os.spawn*(),
• os.popen*()
• popen2.*()
• commands.*()

使用subprocess模块，主要会用到它的Popen类

1、命令以序列的方式执行.

>>> proc = subprocess.Popen(['ls', '-l'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>> stdout, stderr = proc.communicate()         # 获取标准输入和标准输出

2、命令以字符串的方式执行

>>> proc = subprocess.Popen('ls -l', stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
>>> stdout, stderr = proc.communicate()        # 获取标准输出和标准错误

• 命令可以用字符串或序列，如果是序列，shell参数应该为Flase (默认)， 如果是字符串，shell参数为True，如果shell=True它会在linux shell里面执行，官方文档推荐命令以序列的方式执行，因为用字符串可能会有歧义。
• communicate 方法可以从process中获取到标准输出和错误

练习：

def sh(cmdline):
    """
    : 执行shell命令返回结果, 等同于subprocess.getoutput(cmdline)
    : params: cmdline 命令
    : return : str
    """
    process = subprocess.Popen(cmdline, stdout=subprocess.PIPE,
                               stderr=subprocess.PIPE, shell=True)
    process.wait()
    stdout, stderr = process.communicate()

    if stdout:
        return str(stdout.strip(), encoding='utf-8')
    if stderr:
        return str(stderr.strip(), encoding='utf-8')

Python3中还支持几个方法：

• getoutput    获取命令的执行结果，返回str
• getstatusoutput 获取命令执行的返回值、结果，返回tuple

getoutput

>>> subprocess.getoutput('ls -l')
'total 261868
-rw-------. 1 root root      2769 Mar 27  2016 anaconda-ks.cfg
-rw-r--r--  1 root root       295 May 14 12:28 bash.py
-rw-------  1 root root      3485 Apr 14 15:54 dead.letter
-rwxr-xr-x  1 root root       591 Apr 27 10:07 get_estab.py
drwxr-xr-x  5 root root      4096 Jan 13 15:38 gitdir
-rw-r--r--  1 root root    174895 Nov  2  2016 google.log
-rwxr-xr-x  1 root root      3351 Apr 28 09:02 homework.py
-rw-r--r--  1 root root       255 Nov 28 21:52 init_hostname.sh
-rw-r--r--. 1 root root     20341 Mar 27  2016 install.log
-rw-r--r--  1 root root       306 May 13 22:47 iw.py
drwxr-xr-x  3 root root      4096 Apr 24 16:31 learpython
-rwxr-xr-x  1 root root       725 Apr 18 17:21 monitor_zh.sh
drwxr-xr-x  2 root root      4096 Apr 22 00:30 openapi
-rw-r--r--  1 root root 189688255 Dec 12 19:40 openapi.out
-rw-r--r--  1 root root  78200937 Nov  2  2016 pic_access.log
drwxr-xr-x  3 root root      4096 Mar 30 21:09 ps_mem
-rw-r--r--  1 root root      1765 Apr 28 17:13 userdb.pkl'

getstatusoutput

>>> subprocess.getstatusoutput('ls -l')
(0, 'total 261868
-rw-------. 1 root root      2769 Mar 27  2016 anaconda-ks.cfg
-rw-r--r--  1 root root       295 May 14 12:28 bash.py
-rw-------  1 root root      3485 Apr 14 15:54 dead.letter
-rwxr-xr-x  1 root root       591 Apr 27 10:07 get_estab.py
drwxr-xr-x  5 root root      4096 Jan 13 15:38 gitdir
-rw-r--r--  1 root root    174895 Nov  2  2016 google.log
-rwxr-xr-x  1 root root      3351 Apr 28 09:02 homework.py
-rw-r--r--  1 root root       255 Nov 28 21:52 init_hostname.sh
-rw-r--r--. 1 root root     20341 Mar 27  2016 install.log
-rw-r--r--  1 root root       306 May 13 22:47 iw.py
drwxr-xr-x  3 root root      4096 Apr 24 16:31 learpython
-rwxr-xr-x  1 root root       725 Apr 18 17:21 monitor_zh.sh
drwxr-xr-x  2 root root      4096 Apr 22 00:30 openapi
-rw-r--r--  1 root root 189688255 Dec 12 19:40 openapi.out
-rw-r--r--  1 root root  78200937 Nov  2  2016 pic_access.log
drwxr-xr-x  3 root root      4096 Mar 30 21:09 ps_mem
-rw-r--r--  1 root root      1765 Apr 28 17:13 userdb.pkl')

封装一个可以执行linux命令的函数

import sys
import subprocess

PY2 = sys.version_info[0] == 2

if not PY2:
    # is py3 or later
    def sh(cmd, retcode=False):
        """
        run command on the Linux system
        return: a tuple or str
        """
        if not retcode:
            return subprocess.getoutput(cmd)
        return subprocess.getstatusoutput(cmd)
else:
    # is py2
    def sh(cmd, retcode=False):
        process = subprocess.Popen(
            cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
        process.wait()
        stdout, stderr = process.communicate()
        returncode = process.returncode
        if stderr:
            if retcode:
                return returncode, stderr
            return stderr
        if retcode:
            return returncode, stdout
        return stdout

if __name__ == '__main__':
    print(sh('route -n', retcode=True))
    print(sh('route'))