Python Subprocess Hangs

I'm executing the following subprocess... p.call(['./hex2raw', '<', 'exploit4.txt', '|', './rtarget']) ...and it hangs. But if I execute kmwe236@kmwe236:~/CS485/prog3/target26$

Solution 1:

Since you're using redirection and piping, you have to enable shell=True

sp.call(["./hex2raw", "<", "exploit4.txt", "|", "./rtarget"],shell=True)

but it would be much cleaner to use Popen on both executables and feeding the contents of exploit4.txt as input. Example below, adapted to your case:

import subprocess

    with open("exploit4.txt") as inhandle:
        p = subprocess.Popen("./hex2raw",stdin=inhandle,stdout=subprocess.PIPE)
        p2 = subprocess.Popen("./rtarget",stdin=p.stdout,stdout=subprocess.PIPE)
        [output,error] = p2.communicate()
        print(output)
        # checking return codes is also a good idea
        rc2 = p2.wait()
        rc = p.wait()

Explanation:

1. open the input file, get its handle inhandle
2. open the first subprocess, redirecting stdin with inhandle, and stdout to an output stream. Get the pipe handle (p)
3. open the second subprocess, redirecting stdin with previous process stdout, and stdout to an output stream
4. let the second process communicate. It will "pull" the first one by consuming its output: both processes work in a pipe fashion
5. get return codes and print the result

Note: you get "format error" because one or both executables are actually shell or other non-native executables. In that case, just add the shell=True option to the relevant Popen calls.