In my python script, I am trying to run a windows program that prints output. But I would like to redirect that output to a text file. I tried
command = 'program' + arg1 + ' > temp.txt'
subprocess.call(command)
Where program is my program name and arg1 is argument it takes. but it does not redirect the output to the text file It just prints that on the screen.
Can anyone help me how to do this? Thank you!
Pass a file object to the stdout parameter of subprocess.call():
with open('myoutfilename', 'w') as myoutfile:
subprocess.call(cmd, stdout=myoutfile)
shell=True), but you're right about stdout being one of the key pieces to this.
cmd can be a string, even if there are arguments—and, in fact, quoting the docs, "if args is a sequence, it will be converted to a string in a manner described in Converting an argument sequence to a string on Windows. This is because the underlying CreateProcess() operates on strings.`You can use shell=True in subprocess.call
However, a (much) better way to do this would be:
command = ['program',arg1]
with open('temp.txt','w') as fout:
subprocess.call(command,stdout=fout)
This removes the shell from the whole thing making it more system independent, and it also makes your program safe from "shell injection" attacks (consider arg1='argument; rm -rf ~' or whatever the windows equivalent is).
The context manager (with statement) is a good idea as it guarantees that your file object is properly flushed and closed when you leave the "context".
Note that it is important that if you're not using shell=True to a subprocess.Popen (or similar) class, you should pass the arguments as a list, not a string. Your code will be more robust that way. If you want to use a string, python provides a convenience function shlex.split to split a string into arguments the same way your shell would. e.g.:
import subprocess
import shlex
with open('temp.txt','w') as fout:
cmd = shlex.split('command argument1 argument2 "quoted argument3"'
#cmd = ['command', 'argument1', 'argument2', 'quoted argument3']
subprocess.call(cmd,stdout=fout)