In Python 3.5+ to redirect the output, just pass an open file handle for the stdout
argument to subprocess.run
:
# Use a list of args instead of a string
input_files = ['file1', 'file2', 'file3']
my_cmd = ['cat'] + input_files
with open('myfile', "w") as outfile:
subprocess.run(my_cmd, stdout=outfile)
As others have pointed out, the use of an external command like cat
for this purpose is completely extraneous.