python调用shell命令小结
在写python脚本的时候，经常需要调用系统命令，常用的python调用系统命令的方法主要有subprocess.call和os.popen。默认情况下subprocess.call的方法结果是返回值，即1或0，而os.popen则是命令运行的结果，可以用readlines(读取所有行，返回数组)或者read(读读取所有行，返回str)来读取。subprocess类总主要的方法有：subprocess.call:开启子进程,开启子进程，运行命令，默认结果是返回值，不能trysubprocess.check_call:运行命令，默认结果是返回值，可以try
subprocess.check_out(2.7中才有这个方法) 开启子进程，运行命令，可以获取命令结果，可以try
subprocess.Popen 开启子进程，运行命令，没有返回值，不能try，可以获取命令结果subprocess.PIPE 初始化stdin,stdout,stderr,表示与子进程通信的标准流
Popen.poll 检查子进程是否结束，并返回returncode
Popen.wait等待子进程是否结束，并返回retrurncode
比如check_call的sample:import subprocess
import traceback
cmd='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()分析subprocess的源码：class CalledProcessError(Exception): #首先定义了一个exception，用来在check_call和 check_output中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wait
def check_call(*popenargs, **kwargs):
retcode = call(*popenargs, **kwargs)#调用call,返回返回值
if retcode:
cmd = kwargs.get("args")
if cmd is None:
cmd = popenargs
raise CalledProcessError(retcode, cmd)#可以抛出异常
return 0 def 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，并返回returncode
if retcode:
cmd = kwargs.get("args")
if cmd is None:
cmd = popenargs
raise CalledProcessError(retcode, cmd, output=output)
return output</pre>有时候我们需要在运行命令时可以获取返回值，获取结果，并且能够try。<span style="font-family:'宋体';"></span><span style="font-family:'宋体';">可以对上面的代码进行组合<br /></span><pre class="brush:python;toolbar:false"># -*- coding: utf8 -*- import exceptions
import subprocess
import traceback
class 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 "命令运行错误:'%s',返回值: %s,错误信息： %s" % (self.cmd, str(self.returncode) ,self.errorlog) def run_command_all(*popenargs, **kwargs):
allresult = {}
cmd = popenargs
if 'stdout' in kwargs or 'stderr' in kwargs :
raise ValueError('标准输出和标准错误输出已经定义，不需设置。')
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 allresult if __name__ == '__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()
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