Create and pipe a file-like object as input for a command

Question

I'm looking for a better way to do this, if possible:

import subprocess

f = open('temp.file', 'w+')
f.write('hello world')
f.close()

out = subprocess.check_output(['cat', 'temp.file'])

print out

subprocess.check_output(['rm', 'temp.file'])

In this example I'm creating a file and passing it as input to cat (in reality it's not cat I'm running but some other program that parses an input pcap file).

What I'm wondering is, is there a way in Python I can create a 'file-like object' with some content, and pipe this file-like object as input to a command-line program. If it is possible, I reckon it would be more efficient than writing a file to the disk and then deleting that file.

Answer 1

check_output takes a stdin input argument to specify a file-like object to connect to the process's standard input.

with open('temp.file') as input:
    out = subprocess.check_output(['cat'], stdin=input)

Also, there's no need to shell out to run rm; you can remove the file directly from Python:

os.remove('temp.file')

Answer 2

You can write to a TemporaryFile

import subprocess
from tempfile import TemporaryFile
f = TemporaryFile("w")
f.write("foo")
f.seek(0)
out = subprocess.check_output(['cat'],stdin=f)

print(out)
b'foo'

If you just want to write to a file like object and get the content:

from io import StringIO
f = StringIO()
f.write("foo")

print(f.getvalue())