'subprocess.check_output' extra new line?
sbremal at hotmail.com
sbremal at hotmail.com
Fri Jan 4 12:51:33 EST 2013
Very good point, you are absolutely right:
# cygpath C:\\ | od -c
0000000 / c y g d r i v e / c \n
0000014
'bash' manual also confirms it:
Command Substitution
Command substitution allows the output of a command to replace the command name. There are two
forms:
$(command)
or
`command`
Bash performs the expansion by executing command and replacing the command substitution with the
---> standard output of the command, with any trailing newlines deleted. Embedded newlines are not
deleted, but they may be removed during word splitting. The command substitution $(cat file) can be
replaced by the equivalent but faster $(< file).
When the old-style backquote form of substitution is used, backslash retains its literal meaning
except when followed by $, `, or \. The first backquote not preceded by a backslash terminates the
command substitution. When using the $(command) form, all characters between the parentheses make up
the command; none are treated specially.
Command substitutions may be nested. To nest when using the backquoted form, escape the inner back-
quotes with backslashes.
If the substitution appears within double quotes, word splitting and pathname expansion are not per-
formed on the results.
Cheers
B.
----------------------------------------
> Date: Sat, 5 Jan 2013 03:14:46 +1100
> Subject: Re: 'subprocess.check_output' extra new line?
> From: rosuav at gmail.com
> To: python-list at python.org
>
> On Sat, Jan 5, 2013 at 2:50 AM, <sbremal at hotmail.com> wrote:
> >
> > Hi
> >
> > I wonder if the additional new line charachter at the end of the standard output capture is on purpose with 'subprocess.check_output'?
> >
> >>>> subprocess.check_output([ 'cygpath', 'C:\\' ])
> > '/cygdrive/c\n'
> >
> > If I do the same from the shell there is no extra new line (which is correct I believe):
> >
> > $ x=$(cygpath C:\\); echo "_${x}_"
> > _/cygdrive/c_
> >
> > Surely I have a workaround. I was more interested whether it was a design flaw.
>
> What you may have there is the shell $( ) handling changing the
> program's output. Try piping the command into 'hd' or similar to see
> what it actually produces; it's entirely possible the \n is there, and
> the shell is stripping it.
>
> In any case, you can easily trim whitespace from inside Python. That
> would be your workaround, I think.
>
> ChrisA
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