Unknown shorthand flag: 'E' in -E

Question

I am trying to execute a bash command in python

The bash command I want to execute is: kubectl get ns | grep -E '(^|\s)OK($|\s)'

And in python I do this like this:

is_namespace_exists = subprocess.call(["kubectl", "get", "ns", "|", "grep", "-E", "\'(^|\s)"+NAMESPACE+"($|\s)\'"])

and

is_namespace_exists = subprocess.call(["kubectl", "get", "ns", "|", "grep", "-E", "'(^|\s)"+NAMESPACE+"($|\s)'"])

But I get this error:

unknown shorthand flag: 'E' in -E

Can someone tell me what is going wrong?

when I execute this in a normal terminal it works. When I execute it using the python it doesn't. — Jananath Banuka, Nov 27 '19 at 14:48
I retract my previous comment. It's interpreted as argument to `kubectl`, since `|` has no meaning to `subprocess`. It only has a meaning in a shell. `subprocess` doesn't parse the command through a shell. — deceze, Nov 27 '19 at 14:49
You need to use `shell=True` in your `subprocess.call` call, and pass it a string rather than a list. — larsks, Nov 27 '19 at 14:52
I'd probably prefer to just execute `['kubectl', 'get', 'ns']`, and do the tiny bit of string processing in Python afterwards. — deceze, Nov 27 '19 at 14:52

score 2 · Accepted Answer · answered Nov 27 '19 at 15:09

The following code should work:

import subprocess

NAMESPACE = "..."  # Define NAMESPACE variable here

proc1 = subprocess.Popen(['kubectl', 'get', 'ns'], stdout=subprocess.PIPE)
proc2 = subprocess.Popen(["grep", "-E", "\'(^|\s)"+NAMESPACE+"($|\s)\'"], stdin=proc1.stdout, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

proc1.stdout.close() # Allow proc1 to receive a SIGPIPE if proc2 exits.
out, err = proc2.communicate()
print('out: {0}'.format(out))
print('err: {0}'.format(err))

Basically an adaptation of this post. Adapt according to your needs.

Unknown shorthand flag: 'E' in -E

1 Answers1