python执行shell命令

jiaoc

　　1 os.system
　　可以返回运行shell命令状态，同时会在终端输出运行结果
　　例如 ipython中运行如下命令，返回运行状态status



os.system('cat /etc/passwdqc.conf')
min=disabled,24,11,8,7
max=40
passphrase=3
match=4
similar=deny
random=47
enforce=everyone
retry=3
Out[6]: 0
　　
　　2 os.popen()
　　可以返回运行结果



popen(command [, mode='r' [, bufsize]]) -> pipe
Open a pipe to/from a command returning a file object.
　　运行返回结果



In [20]: output = os.popen('cat /proc/cpuinfo')
In [21]: lineLen = []
In [22]: for line in output.readlines():
lineLen.append(len(line))
....:     
In [23]: line
line     lineLen  
In [23]: lineLen
Out[23]:
[14,
25,
...
　　
　　3 如何同时返回结果和运行状态，commands模块:



#String form: <module 'commands' from '/usr/lib64/python2.7/commands.pyc'>
File: /usr/lib64/python2.7/commands.py
Docstring:
Execute shell commands via os.popen() and return status, output.
Interface summary:
import commands
outtext = commands.getoutput(cmd)
(exitstatus, outtext) = commands.getstatusoutput(cmd)
outtext = commands.getstatus(file) # returns output of "ls -ld file"

A trailing newline is removed from the output string.
Encapsulates the basic operation:
pipe = os.popen('{ ' + cmd + '; } 2>&1', 'r')
text = pipe.read()
sts = pipe.close()
　　commands示例如下:



In [24]: (status, output) = commands.getstatusoutput('cat /proc/cpuinfo')
In [25]: status
Out[25]: 0
In [26]: len(output)
Out[26]: 3859
　　
　　4 使用模块subprocess
　　ipython 中运行"?subprocess"可以发现subprocess是python用来替换os.popen()等管道操作命令的新模块



A more real-world example would look like this:
try:
retcode = call("mycmd" + " myarg", shell=True)
if retcode < 0:
print >>sys.stderr, "Child was terminated by signal", -retcode
else:
print >>sys.stderr, "Child returned", retcode
except OSError, e:
print >>sys.stderr, "Execution failed:", e
　　相对于上面几种方式，subprocess便于控制和监控进程运行结果,subprocess提供多种函数便于应对父进程对子进程不同要求:
　　4.1.1 subprocess.call()
　　父进程父进程等待子进程完成，返回exit code
　　4.1.2 subprocess.check_call()
　　父进程等待子进程完成,返回0，如果returncode不为0，则举出错误subprocess.CalledProcessError，该对象包含有returncode属性，可用try...except...来检查
　　4.1.3 subprocess.check_output()
　　父进程等待子进程完成
　　返回子进程向标准输出的输出结果
　　检查退出信息，如果returncode不为0，则举出错误subprocess.CalledProcessError，该对象包含有returncode属性和output属性，output属性为标准输出的输出结果，可用try...except...来检查
　　例如:



In [32]: out = subprocess.call("ls -l", shell=True)
total 42244
-rw-rw-r--.  1 *** ***     366 May 26 09:10 ChangeLog
　　4.2.1
　　上面三个函数都是源于Popen()函数的wapper(封装),如果需要更加个性化应用，那么就需要使用popen()函数
　　Popen对象创建后，主程序不会自动等待子进程完成。我们必须调用对象的wait()方法，父进程才会等待 (也就是阻塞block)



[wenwt@localhost syntax]$ rm subprocess.pyc
[wenwt@localhost syntax]$ python process.py
parent process
[wenwt@localhost syntax]$ PING www.google.com (173.194.219.99) 56(84) bytes of data.
^C
[wenwt@localhost syntax]$
--- www.google.com ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 3999ms
　　加上wait方法:



[wenwt@localhost syntax]$ python process.py
PING www.google.com (173.194.219.103) 56(84) bytes of data.
--- www.google.com ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 3999ms
parent process
　　
　　参考文章:Python标准库06 子进程 (subprocess包)