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Date: Mon, 08 Oct 2012 08:53:46 +0800
From: =?UTF-8?B?5Y+25L2R576k?= <ye.youqun@eisoo.com>
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To: Kushal Kumaran <kushal.kumaran+python@gmail.com>
Subject: Re: how to run shell command like "<<EOT .... EOT"
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于 2012-9-29 19:53, Kushal Kumaran 写道:
> On Sat, Sep 29, 2012 at 6:18 AM, 叶佑群<ye.youqun@eisoo.com>  wrote:
>> 于 2012-9-28 16:16, Kushal Kumaran 写道:
>>> On Fri, Sep 28, 2012 at 1:15 PM, 叶佑群<ye.youqun@eisoo.com>   wrote:
>>>
>>>> Hi, all,
>>>>
>>>>       I have the shell command like this:
>>>>
>>>> sfdisk -uM /dev/sdb<<   EOT
>>>> ,1000,83
>>>> ,,83
>>>> EOT
>>>>
>>>>
>>>>       I have tried subprocess.Popen, pexpect.spawn and os.popen, but none
>>>> of
>>>> these works, but when I type this shell command in shell, it is works
>>>> fine.
>>>> I wonder how to emulate this type of behavior in python , and if someone
>>>> can
>>>> figure out the reason why?
>>>>
>>>>       The sample code of subprocess.Popen is:
>>>>
>>>>       command = ["sfdisk", "-uM",  target, "<<EOT", "\r\n",
>>>>                   ",", 1000, ",", "83", "\r\n",
>>>>                   ",", ",", "83", "\r\n", "EOT", "\r\n"]
>>>>
>>>>       pobj = subprocess.Popen (command, bufsize=1, \
>>>>                           stderr=subprocess.PIPE, stdout=subprocess.PIPE)
>>>>
>>>>       res = pobj.stderr.readline ()
>>>>       if res is not None and pobj.returncode != 0:
>>>>           observer.ShowProgress (u"对设备 %s 分区失败！" % target)
>>>>           return False
>>>>
>>> The "<<EOT" syntax (called a here-document) just provides input to the
>>> command.  If you use the communicate method, you can provide input as
>>> an argument:
>>>
>>> command = ["sfdisk", "-uM",  target ]
>>> instructions = """
>>> ,1000,83
>>> ,,83
>>> """
>>> pobj = subprocess.Popen(command, stdin=subprocess.PIPE,
>>> stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>> (output, errors) = pobj.communicate(instructions)
>> I tried this, but it is still not work.
>>
> What do you mean by "not work"?
Sorry for replying so late, these days are long vocation in china.

If I type command in shell line by line, the command will run as 
expected, but when I invoke the command in python, it is always failed. 
Which is what I mean "not work".


>
> - If you get an exception, copy the entire traceback into an email
No exception occured.
>
> - If you do not get an exception, print out the value of the "errors"
> variable to see why the command failed.  You can also check
> pobj.returncode for the exit status of the subprocess.
I solved this problem as below:

fop = os.popen ("sfdisk -uM %s <<EOT\n,%d,83\n,,83\nEOT\n" % (target, fps))

But when I run it with subprocess.Popen (), it doesn't work as os.popen 
even use the code as:

command = ["sfdisk", "-uM",  target ]
instructions = """
,1000,83
,,83
"""

pobj = subprocess.Popen(command, stdin=subprocess.PIPE,
stdout=subprocess.PIPE, stderr=subprocess.PIPE)
(output, errors) = pobj.communicate(instructions)

stderr.readline () always return the error message means "sfdisk won't accept more than one device parameter except -s or -l is specified", it seems that some parameters were incorrectly treated

>
> A possibility is that you have to replace "sfdisk" with the full path
> to the binary, if it cannot be located on the PATH.  So you will
> replace it with "/usr/sbin/sfdisk", or "/sbin/sfdisk", or wherever the
> file actually is.
>
> <from your other email>
>> If I want to read the output line by line and not put all output to memory buffer in one
>> time, how to write the code?
> You can read line by line by calling pobj.stdout.readline() and
> pobj.stderr.readline().  You can send input to the process by calling
> pobj.stdin.write().  If you manage this interaction "by hand", you
> should not call communicate().  Also, you should be aware of the
> problem mentioned in the subprocess documentation:
>
> "Use communicate() rather than .stdin.write, .stdout.read or
> .stderr.read to avoid deadlocks due to any of the other OS pipe
> buffers filling up and blocking the child process."
>
> Is there any reason why you need to read line-by-line?  You could use
> communicate(), and then call stdout.splitlines() to get a list of
> lines, if that's all you need.
>