piping with subprocess

[Peter Otten]

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.