piping with subprocess

Mark Lawrence breamoreboy at yahoo.co.uk
Sat Feb 1 15:28:41 CET 2014


On 01/02/2014 13:54, Rick Dooling wrote:
> On Saturday, February 1, 2014 6:54:09 AM UTC-6, Peter Otten wrote:
>> Rick Dooling wrote:
>>
>>
>>
>>> I spent half a day trying to convert this bash script (on Mac)
>>
>>>
>>
>>> textutil -convert html $1 -stdout | pandoc -f html -t markdown -o $2
>>
>>>
>>
>>> into Python using subprocess pipes.
>>
>>>
>>
>>> It works if I save the above into a shell script called convert.sh and
>>
>>> then do
>>
>>>
>>
>>> subprocess.check_call(["convert.sh", file, markdown_file])
>>
>>>
>>
>>> where file and markdown_file are variables.
>>
>>>
>>
>>> But otherwise my piping attempts fail.
>>
>>
>>
>> It is always a good idea to post your "best effort" failed attempt, if only
>>
>> to give us an idea of your level of expertise.
>>
>>
>>
>>> Could someone show me how to pipe in subprocess. Yes, I've read the doc,
>>
>>> especially
>>
>>>
>>
>>> http://docs.python.org/2/library/subprocess.html#replacing-shell-pipeline
>>
>>>
>>
>>> But I'm a feeble hobbyist, not a computer scientist.
>>
>>
>>
>> Try to convert the example from the above page
>>
>>
>>
>> """
>>
>> output=`dmesg | grep hda`
>>
>> # becomes
>>
>> p1 = Popen(["dmesg"], stdout=PIPE)
>>
>> p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
>>
>> p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
>>
>> output = p2.communicate()[0]
>>
>> """
>>
>>
>>
>> to your usecase. Namely, replace
>>
>>
>>
>> ["dmesg"] --> ["textutil", "-convert", "html", infile, "-stdout"]
>>
>> ["grep", "hda"] --> ["pandoc", "-f", "html", "-t", "marktown", "-o",
>>
>>                       outfile]
>>
>>
>>
>> Don't forget to set
>>
>>
>>
>> infile = ...
>>
>> outfile = ...
>>
>>
>>
>> to filenames (with absolute paths, to avoid one source of error).
>>
>> If that doesn't work post the code you wrote along with the error messages.

Would you please read and action this 
https://wiki.python.org/moin/GoogleGroupsPython to prevent us seeing the 
double line spacing above, thanks.

-- 
My fellow Pythonistas, ask not what our language can do for you, ask 
what you can do for our language.

Mark Lawrence




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