Expanding/substituting variables in a popen call

Question

I'm trying to call some shell program that use the environment and I'm trying to figure out the correct way. I boiled down to this snippet: ``` import subprocess as sp p = sp.Popen(["echo","Hello","$FOO"], env = {"FOO":"42"}, stdout = sp.PIPE, shell = True) p.wait() print(p.communicate()) ``` When "shell" is set to True it prints "('
', None)" and when it's set to False it prints "('Hello $FOO
', None)", but I was expecting it to print something along the lines of "('Hello 43
', None)". What I'm doing wrong and is there a better way to do it?

Accepted Answer

Try this:

```
p = sp.Popen("echo Hello $FOO", env={"FOO":"42"}, shell=True)
```

The output should be "Hello 42"

Expanding/substituting variables in a popen call

Solution

Problem