Calling Bash Command From Python

[Jon Ribbens]

On 2016-10-31, Wildman <best_lay at yahoo.com> wrote:
> Here is a bash command that I want to run from a python
> program:  sudo grep "^user\:" /etc/shadow
>
> If I enter the command directly into a terminal it works
> perfectly.  If I run it from a python program it returns an
> empty string.  Below is the code I am using.  Suggestions
> appreciated.
>
> cmdlist = ["sudo", "grep", '"^$USER\:"', "/etc/shadow"]
> p = subprocess.Popen(cmdlist,
>                      stdout=subprocess.PIPE,
>                      stderr=subprocess.PIPE)
> shadow, err = p.communicate()
> print shadow

Slightly surprised that nobody's pointed out that in your bash
invocation, the first argument to grep is:

    ^user\:

and in the Python code it is:

    "$USER\:"

Your cmdlist should read:

    ["sudo", "grep", r"^user\:", "/etc/shadow"]

or if you really want it to do the same as the bash:

    ["sudo", "grep", "^" + os.environ["USER"] + r"\:", "/etc/shadow"]