Knowledge points of shell execution in python

os.system

The system method creates a child process to run an external program, and the method only returns the results of the external program. This method is more suitable for situations where the external program has no output results.

import os
os.system('ls')

commands.getstatusoutput

Use the getoutput method of the commands module. The difference between this method and popend is that popen returns a file handle, while this method returns the output result of an external program as a string, which is more convenient in many cases.

Main method:

• commands.getstatusoutput(cmd) returns (status, output)
• commands.getoutput(cmd) only returns the output result
• commands.getstatus(file) returns the execution result string of ls -ld file. Getoutput is called. This method is not recommended

This method is very useful when you need to get the output result of an external program. For example, when using urllib to call Web API, you need to process the obtained data. os.popen(cmd) To get the output of the command, just call read() or readlines() again, such as a=os.popen(cmd).read()

import os
ls = os.popen('ls')
print ls.read()

commands.getstatusoutput

Use the getoutput method of the commands module. The difference between this method and popend is that popen returns a file handle, while this method returns the output result of an external program as a string, which is more convenient in many cases.
Main method:

• commands.getstatusoutput(cmd) returns (status, output)
• commands.getoutput(cmd) only returns the output result
• commands.getstatus(file) returns the execution result string of ls -ld file. Getoutput is called. This method is not recommended

import commands
commands.getstatusoutput('ls -lt')   #return(status, output)

subprocess.call

According to the official Python documentation, the subprocess module is used to replace these modules. There is a parallel ssh tool implemented in Python-mssh, the code is very short, but very interesting, it calls subprocess in the thread to start the child process to work.

from subprocess import call
call(["ls","-l"])

import shlex, subprocess
def shell_command(cmd, timeout):
 data ={"rc":False,"timeout":False,"stdout":"","stderr":""}try:
 process = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)try:
  outs, errs = process.communicate(timeout=timeout)
  data["stdout"]= outs.decode("utf-8") 
  data["stderr"]= errs.decode("utf-8") 
  data["rc"]= True

 except subprocess.TimeoutExpired :
  process.kill()
  outs, errs = process.communicate()
  data["rc"]= False 
  data["stdout"]= outs.decode("utf-8") 
  data["stderr"]="timeout"
  data["timeout"]= True 

 except Exception as e :
 data["rc"]= False 
 data["stderr"]= e 

 finally:return data 

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