Malformed environment variables detection in python

Question

I am trying to source a bash script containing some environment variables in python. I followed one other thread to do it. But, there seems that one of the variable is malformed, as can be seen in the given snippet.

COLORTERM=gnome-terminal
mc=() {  . /usr/share/mc/mc-wrapper.sh
}
_=/usr/bin/env

I am using the following code to set up the current environment.

import os
import pprint
import subprocess

command = ['bash', '-c', 'source init_env && env']

proc = subprocess.Popen(command, stdout = subprocess.PIPE)

for line in proc.stdout:
    (key, _, value) = line.partition("=")
    os.environ[key] = value

proc.communicate()

'

If I change the above code a little like putting a condition:

for line in proc.stdout:
    (key, _, value) = line.partition("=")
    if not value:
        continue
    os.environ[key] = value

then things are working but the environment is corrupted because of one missing bracket as can be seen from the snippet of environment variable that the bracket is appearing on new line. Because of this corruption, If I run some other command like

os.system("ls -l")

it gives me the following error

sh: mc: line 1: syntax error: unexpected end of file
sh: error importing function definition for `mc'

What could be the possible solutions for this problem?

Thanks alot

Where does the snippet come from? If there is a syntax error in a shell script, can't you fix the shell script? But this looks like a valid shell function, only printed in a form which isn't suitable for direct evaluation. — tripleee
– tripleee, Commented Feb 16, 2012 at 7:36
That is not malformed, that is its value going over several lines. Newlines are allowed. Your ls call dumps errors because you have assigned invalid body to "mc" function during execution of os.environ[key] = value statement. What are you trying to accomplish here? — hamstergene
– hamstergene, Commented Feb 16, 2012 at 9:13
I just want my environment variable to appear in python environment. Is there any other way to do this? Or how am I going to deal with environment variable's value which is spanning on multiple lines? — Shahzad
– Shahzad, Commented Feb 16, 2012 at 9:26
@Shahzad: Rather than invoking Bash from Python and trying to read environment-variables over a pipe, wouldn't it be easier to just invoke Python from Bash? Just run source init_env before running your Python script. — ruakh
– ruakh, Commented Feb 16, 2012 at 15:40
Unfortunately, no. I cannot do this because its a complete and complex project spanning over several files. — Shahzad
– Shahzad, Commented Feb 16, 2012 at 16:51

ruakh · Accepted Answer · 2012-02-16 18:19:35Z

1

Probably the best way to do this is to create a separate program that writes out the environment variables in a way that is easily and unambiguously processed by your own program; then call that program instead of env. Using the standard pickle module, that separate program can be as simple as this:

import os
import sys
import pickle

pickle.dump(os.environ, sys.stdout)

which you can either save into its own .py file, or else put directly in a Bash command:

python -c 'import os, sys, pickle; pickle.dump(os.environ, sys.stdout)'

In either case, you can process its output like this:

import os
import pprint
import subprocess
import pickle

command = [
      'bash',
      '-c',
      'source init_env && ' +
         'python -c "import os, sys, pickle; ' +
                    'pickle.dump(os.environ, sys.stdout)"'
]

proc = subprocess.Popen(command, stdout = subprocess.PIPE)

for k, v in pickle.load(proc.stdout).iteritems():
    os.environ[k] = v

proc.communicate()

answered Feb 16, 2012 at 18:19

ruakh

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1 Comment

Shahzad Over a year ago

Thanks alot ruakh. I will try this method and will update you with the feedback. Seems like a good solution to me.

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