我们经常需要通过Python去执行一条系统命令或脚本，系统的shell命令是独立于你的python进程之外的，每执行一条命令，就是发起一个新进程，通过python调用系统命令或脚本的模块在python2有os.system，,commands,popen2等也可以，比较乱，于是官方推出了subprocess,目地是提供统一的模块来实现对系统命令或脚本的调用
"os.system获取不到返回值"
>>> import os
>>> a = os.system("df -h")
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 98G 1.9G 97G 2% /
devtmpfs 479M 0 479M 0% /dev
tmpfs 489M 0 489M 0% /dev/shm
tmpfs 489M 6.7M 482M 2% /run
tmpfs 489M 0 489M 0% /sys/fs/cgroup
/dev/sda1 1014M 120M 895M 12% /boot
tmpfs 98M 0 98M 0% /run/user/0
>>> a
0
" os.popen可以获取到返回值"
>>> os.popen("df -h")
<open file 'df -h', mode 'r' at 0x7f95dedd0780>
>>> f = os.popen("df -h")
>>> f.read()
'Filesystem Size Used Avail Use% Mounted on\n/dev/sda3 98G 1.9G 97G 2% /\ndevtmpfs 479M 0 479M 0% /dev\ntmpfs 489M 0 489M 0% /dev/shm\ntmpfs 489M 6.7M 482M 2% /run\ntmpfs 489M 0 489M 0% /sys/fs/cgroup\n/dev/sda1 1014M 120M 895M 12% /boot\ntmpfs 98M 0 98M 0% /run/user/0\n'
"python2中的commands模块"
>>> import commands
>>> commands.getstatusoutput("df -h")
(0, 'Filesystem Size Used Avail Use% Mounted on\n/dev/sda3 98G 1.8G 97G 2% /\ndevtmpfs 479M 0 479M 0% /dev\ntmpfs 489M 0 489M 0% /dev/shm\ntmpfs 489M 6.7M 482M 2% /run\ntmpfs 489M 0 489M 0% /sys/fs/cgroup\n/dev/sda1 1014M 120M 895M 12% /boot\ntmpfs 98M 0 98M 0% /run/user/0')
subprocess.run(*popenargs, input=None, timeout=None, check=False, **kwargs) #官方推荐
subprocess.call(*popenargs, timeout=None, **kwargs) #跟上面实现的内容差不多，另一种写法
subprocess.Popen() #上面各种方法的底层封装"subprocess.run"
>>> a = subprocess.run(["df","-h"])
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 98G 2.3G 96G 3% /
devtmpfs 479M 0 479M 0% /dev
tmpfs 489M 0 489M 0% /dev/shm
tmpfs 489M 6.8M 482M 2% /run
tmpfs 489M 0 489M 0% /sys/fs/cgroup
/dev/sda1 1014M 120M 895M 12% /boot
tmpfs 98M 0 98M 0% /run/user/0
>>> a.args
['df', '-h']
>>> a.returncode
0
>>> a.check_returncode()
>>> a = subprocess.run(["df","-h"],stdout=subprocess.PIPE,stderr=subprocess.PIPE)
>>> a.stdout
b'Filesystem Size Used Avail Use% Mounted on\n/dev/sda3 98G 2.3G 96G 3% /\ndevtmpfs 479M 0 479M 0% /dev\ntmpfs 489M 0 489M 0% /dev/shm\ntmpfs 489M 6.8M 482M 2% /run\ntmpfs 489M 0 489M 0% /sys/fs/cgroup\n/dev/sda1 1014M 120M 895M 12% /boot\ntmpfs 98M 0 98M 0% /run/user/0\n'
>>> a.stderr
b''
>>> a = subprocess.run(["dsf","-h"],stdout=subprocess.PIPE,stderr=subprocess.PIPE)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/python3Dir/lib/python3.6/subprocess.py", line 403, in run
with Popen(*popenargs, **kwargs) as process:
File "/usr/local/python3Dir/lib/python3.6/subprocess.py", line 709, in __init__
restore_signals, start_new_session)
File "/usr/local/python3Dir/lib/python3.6/subprocess.py", line 1344, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'dsf': 'dsf'
>>> a = subprocess.run(["df","-h","|","grep","a"],stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True)
>>> a.stdout
b'Filesystem 1K-blocks Used Available Use% Mounted on\n/dev/sda3 102709252 2337100 100372152 3% /\ndevtmpfs 490020 0 490020 0% /dev\ntmpfs 499848 0 499848 0% /dev/shm\ntmpfs 499848 6900 492948 2% /run\ntmpfs 499848 0 499848 0% /sys/fs/cgroup\n/dev/sda1 1038336 121872 916464 12% /boot\ntmpfs 99972 0 99972 0% /run/user/0\n'
"subprocess.call"
>>> a = subprocess.call(["df","-h"])
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 98G 2.3G 96G 3% /
devtmpfs 479M 0 479M 0% /dev
tmpfs 489M 0 489M 0% /dev/shm
tmpfs 489M 6.8M 482M 2% /run
tmpfs 489M 0 489M 0% /sys/fs/cgroup
/dev/sda1 1014M 120M 895M 12% /boot
tmpfs 98M 0 98M 0% /run/user/0
>>> "subprocess.Popen会发起新的进程，不影响主进程"
>>> a = subprocess.Popen("sleep 10",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True)#10秒后返回
>>> a = subprocess.Popen("sleep 10",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True)#立刻返回，poll()可以用来监控命令是否结束
>>> a.poll()
>>> a.poll()
>>> a.poll()
0"运行函数"
>>> def sayhi():
print("hello")...
...
>>> sayhi()
hello
>>> a = subprocess.Popen("echo $PWD",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True,preexec_fn=sayhi)
>>> a.stdout.read()
b'hello\n/usr/local/python3/Python-3.6.3\n'
>>>
>>> a = subprocess.Popen("echo $PWD",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True,cwd="/tmp",preexec_fn=sayhi)
>>> a.stdout.read()
b'hello\n/tmp\n'
>>>
>>> a = subprocess.Popen("echo $PWD;sleep 15",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True,cwd="/tmp",preexec_fn=sayhi)
>>> a.wait() #等在这里直到上面的程序运行完成
0
>>>
"Popen程序的终止"
>>> a = subprocess.Popen("echo $PWD;sleep 100",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True)
>>> a.terminate()#程序的终止
>>> a.kill())#程序的终止
>>>
>>> import signal
>>> a = subprocess.Popen("echo $PWD;sleep 100",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True)
>>> a.send_signal(signal.SIGKILL)"communicate()程序交互，只能交互一次,再次交互会报错"
>>> import subprocess
>>> a = subprocess.Popen("python3 guessage.py",stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True)
>>> a.communicate(b'33')
(b'input the age of you think:you should input one number!\ninput the age of you think:you should input one number!\ninput the age of you think:you should input one number!\n', b'')
>>>
>>> a.communicate(b'12')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/python3Dir/lib/python3.6/subprocess.py", line 818, in communicate
raise ValueError("Cannot send input after starting communication")
ValueError: Cannot send input after starting communication
>>>
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