Running a C executable from Python with command line arguments

Question

I have a C file say, myfile.c.

Now to compile I am doing : gcc myfile.c -o myfile

So now to run this I need to do : ./myfile inputFileName > outputFileName

Where inputFileName and outputFileName are 2 command line inputs.

Now I am trying to execute this within a python program and I am trying this below approach but it is not working properly may be due to the >

import subprocess
import sys

inputFileName = sys.argv[1];
outputFileName = sys.argv[2];

subprocess.run(['/home/dev/Desktop/myfile', inputFileName, outputFileName])

Where /home/dev/Desktop is the name of my directory and myfile is the name of the executable file.

What should I do?

You should be a able to directly run the C file from python as a module. Please take a look at this stackoverflow question which can lead to this Python documentation. — Kevin H
– Kevin H, Commented Nov 8, 2021 at 16:45
Is the author perhaps missing the '>' in their subprocess command? — Aurgho Bhattacharjee
– Aurgho Bhattacharjee, Commented Nov 8, 2021 at 16:46
> outputFileName is ouput redirection. It's something your shell is doing - it's not an argument to your program. To reproduce that with python, look at stackoverflow.com/questions/4965159/… — rdas
– rdas, Commented Nov 8, 2021 at 16:46
Does this answer your question? How to make a call to an executable from Python script? — homer
– homer, Commented Nov 8, 2021 at 16:48

Marco Bonelli · Accepted Answer · 2021-11-08 16:52:53Z

1

The > that you use in your command is a shell-specific syntax for output redirection. If you want to do the same through Python, you will have to invoke the shell to do it for you, with shell=True and with a single command line (not a list).

Like this:

subprocess.run(f'/home/dev/Desktop/myfile "{inputFileName}" > "{outputFileName}"', shell=True)

If you want to do this through Python only without invoking the shell (which is what shell=True does) take a look at this other Q&A: How to redirect output with subprocess in Python?

edited Nov 8, 2021 at 16:52

answered Nov 8, 2021 at 16:48

Marco Bonelli

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Barmar · Accepted Answer · 2021-11-08 16:57:57Z

1

You can open the output file in Python, and pass the file object to subprocess.run().

import subprocess
import sys

inputFileName = sys.argv[1];
outputFileName = sys.argv[2];

with open(outputFileName, "w") as out:
    subprocess.run(['/home/dev/Desktop/myfile', inputFileName], stdout=out)

answered Nov 8, 2021 at 16:57

Barmar

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