python執行shell命令

1 os.system

可以返回運行shell命令狀態，同時會在終端輸出運行結果

例如 ipython中運行如下命令，返回運行狀態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()

可以返回運行結果

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

運行返回結果

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 如何同時返回結果和運行狀態，commands模塊:

#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 使用模塊subprocess

通常項目中經常使用方法為subporcess.Popen, 我們可以在Popen()建立子進程的時候改變標准輸入、標准輸出和標准錯誤，並可以利用subprocess.PIPE將多個子進程的輸入和輸出連接在一起，構成管道(pipe):

import subprocess
child1 = subprocess.Popen(["ls","-l"], stdout=subprocess.PIPE)
child2 = subprocess.Popen(["wc"], stdin=child1.stdout,stdout=subprocess.PIPE)
out = child2.communicate()
print(out)

 在例如使用lsblk查看swap分區的uuid：

import subprocess

child = subprocess.Popen(["lsblk", "-f"], stdout=subprocess.PIPE)
out = child.stdout.readlines()

swap_uuid = None
for item in out:
    line = item.strip().split()
    if len(line) == 4:
        if(line[1] == 'swap'):
            swap_uuid = line[2]
print(swap_uuid)

 

ipython 中運行"?subprocess"可以發現subprocess是python用來替換os.popen()等管道操作命令的新模塊

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

相對於上面幾種方式，subprocess便於控制和監控進程運行結果,subprocess提供多種函數便於應對父進程對子進程不同要求:

4.1.1 subprocess.call()

父進程父進程等待子進程完成，返回exit code

4.1.2 subprocess.check_call()

父進程等待子進程完成,返回0，如果returncode不為0，則舉出錯誤subprocess.CalledProcessError，該對象包含有returncode屬性，可用try...except...來檢查

4.1.3 subprocess.check_output()

父進程等待子進程完成

返回子進程向標准輸出的輸出結果

檢查退出信息，如果returncode不為0，則舉出錯誤subprocess.CalledProcessError，該對象包含有returncode屬性和output屬性，output屬性為標准輸出的輸出結果，可用try...except...來檢查

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 

上面三個函數都是源於Popen()函數的wapper(封裝),如果需要更加個性化應用，那么就需要使用popen()函數

Popen對象創建后，主程序不會自動等待子進程完成。我們必須調用對象的wait()方法，父進程才會等待 (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

 

參考文章:Python標准庫06 子進程 (subprocess包)