Python Invoke Shell command summary

When writing Python scripts, it is often necessary to invoke system commands, and common Python methods for invoking system commands are mainly Subprocess.call and Os.popen. By default, the Subprocess.call method results in a return value of 1 or 0, while Os.popen is the result of the command run, which can be read with readlines (read all rows, return an array) or read (read all rows, return str).

The main methods of the subprocess class are:

Subprocess.call: Turn on subprocess, turn on child process, Run command, default result is return value, cannot try

subprocess.check_call: Run command, default result is return value, can try

Subprocess.check_out (this method in 2.7) to open the child process, run the command, you can get the command results, you can try
Subprocess. Popen Open child process, Run command, no return value, cannot try, can get command result

Subprocess. PIPE initialization Stdin,stdout,stderr, which represents the standard flow of communication with the child process
Popen.poll checks if the child process is finished and returns ReturnCode
Popen.wait waits for the child process to end and returns Retrurncode

Like Check_call's sample:

Import Subprocessimport tracebackcmd= ' Hadoop fs-ls hdfs://xxxxx ' Try:e=subprocess.check_call (cmd,shell=true,stdout= Subprocess. PIPE) print "Return code is:%s"% (str (e)) #print stdout.read () except exception,re:print "message is:%s"% (str (re )) Traceback.print_exc ()

Analyze the source code of Subprocess:

Class calledprocesserror (Exception):    #首先定义了一个exception, used in Check_call and  check_ Output in raise exception    def __init__ (self, returncode, cmd,  Output=none):        self.returncode = returncode         self.cmd = cmd         self.output = output    def __str__ (self):         return  "command  '%s '  returned non-zero exit status  %d " %  (self.cmd, self.returncode) ... def call (*popenargs, **kwargs):      return popen (*popenargs, **kwargs). Wait ()    #call方法调用waitdef   Check_call (*popenargs, **kwargs):     retcode = call (*popenargs, ** Kwargs)    #调用call, returns the return value  &NBsp;  if retcode:        cmd = kwargs.get (" Args ")         if cmd is None:             cmd = popenargs[0]         raise calledprocesserror (retcode, cmd)    #可以抛出异常      Return 0def check_output (*popenargs, **kwargs):    if  ' stdout '  in  kwargs:        raise valueerror (' stdout argument  Not allowed, it will be overridden. ')     process = popen (Stdout=pipe, *popenargs, **kwargs)      output, unused_err = process.communicate ()    #获取标准输出和标准错误输出      retcode = process.poll ()     #检查子进程是否结束, and return to Returncode    if retcode:        cmd  = kwargs.get ("args")         if cmd is none:             cmd = popenargs[0]         raise calledprocesserror (Retcode, cmd, output=output)     return output

Sometimes we need to get the return value when we run the command, get the result, and be able to try.

Can be combined with the above code

# -*- coding: utf8 -*-import exceptionsimport subprocessimport  Tracebackclass calledcommanderror (Exception):     def __init__ (self,  Returncode, cmd, errorlog,output):         self.returncode  = returncode        self.cmd = cmd         self.output = output         self.errorlog = errorlog    def __str__ (self):         return  "Command Run Error: '%s ', return value:  %s, error message:  %s"  %  (Self.cmd,  str (Self.returncode)  ,self.errorlog) Def run_command_all (*popenargs, **kwargs):     allresult = {}    cmd = popenargs[0]     if  ' stdout '  in kwargs or  ' stderr '  in kwargs :        raise valueerror (' Standard output and standard error output are already defined and do not need to be set. ')     process = subprocess. Popen (stdout=subprocess. Pipe,shell=true,stderr = subprocess. Pipe,*popenargs, **kwargs)     output, unused_err = process.communicate ()     retcode = process.poll ()     if retcode:          #print  retcode,cmd,unused_err,output         raise calledcommanderror (cmd,retcode,errorlog=unused_err,output=output)      allresult[' cmd '] = cmd    allresult[' ReturnCode '] =  retcode    allresult[' errorlog '] = unused_err    allresult[' Outdata '] = OUTPUT    RETURN ALLRESULTIF __NAME__&Nbsp;==  ' __main__ ':    cmd =  ' hadoop fs -ls xxxx|wc -l '     try:        e=run_command_all (CMD)          print  "OK"     except Exception,re:         print  (str (re))          print  "Failed"         traceback.print_exc ()

This article is from the "Food and Light Blog" blog, please make sure to keep this source http://caiguangguang.blog.51cto.com/1652935/1554549

Python Invoke Shell command summary