Redirect input with subprocess python

Question

How can I use input redirection <() with python's subprocess.Popen?

For example, say I have:

import subprocess
class Test():
 def __init__(self):
 self.proc = subprocess.Popen(["sort file1.txt file2.txt)"],
 shell=True,
 stdout=subprocess.PIPE,
 stderr=subprocess.PIPE)
 def __iter__(self):
 return self
 def __next__(self):
 while True:
 line = self.proc.stdout.readline()
 if not line:
 raise StopIteration
 return line.strip().decode('utf-8')
t = Test()
for line in t:
 print(line)

The above works perfectly fine, but really I need the command to do something like:

sort <(python file1.txt) <(python file2.txt)

That doesnt seem to run anything though, even this doesnt work

sort <(cat file1.txt) <(cat file2.txt)

How can I get this to work with python's subprocess, and iterate through the results line by line

Answer 1

You should tell subprocess.Popen() to use /bin/bash, which supports the <(..) syntax, instead of the default /bin/sh, which doesn't:

 def __init__(self):
 self.proc = subprocess.Popen(["sort <(cat file1.txt) <(cat file2.txt)"],
 shell=True,
 executable="/bin/bash",
 stdout=subprocess.PIPE,
 stderr=subprocess.PIPE)
 def __iter__(self):
 return self
 def __next__(self):
 while True:
 line = self.proc.stdout.readline()
 if not line:
 raise StopIteration
 return line.strip().decode('utf-8')
t = Test()
for line in t:
 print(line)

• user1179317: Great, that works perfectly