I'm having trouble running os.execl() with python 3

Question

import os import sys pid = os.fork() print ("second test") if pid == 0: print ("this is the child") print ("I'm going to exec another program now") os.execl("python", "test.py", * sys.argv) else: print ("the child is pid %d" % pid) os.wait()

I've looked everywhere at examples, but for the life of me, I just can't understand it whatsoever. I thought this would work, but I get this error:

Traceback (most recent call last): File "main.py", line 9, in <module> os.execl("python", "test.py", * sys.argv) File "/usr/local/lib/python3.8/os.py", line 534, in execl execv(file, args) FileNotFoundError: [Errno 2] No such file or directory

Unless this is just a simplified example, use subprocess instead if you are forking just to call execl in the child process. — chepner
– chepner, Commented Mar 11, 2020 at 17:59

Barmar · Accepted Answer · 2020-03-11 17:59:44Z

The first argument to os.execl() should be the path to the executable that you want to run. It won't search for it using $PATH.

You also need to repeat the name of the program as arg0.

os.execl('/usr/local/bin/python', 'python', "test.py", *sys.argv)

You can use os.execlp() to use $PATH to find the program automatically.

os.execlp('python', 'python', "test.py", *sys.argv)

BTW, sys.argv[0] will be the name of the original Python script. You might want to remove that when passing arguments along to another script, so you would use *sys.argv[1:].

And of course, most people use the subprocess module to execute other programs, rather than using fork and exec directly. This provides higher level abstractions to implement I/O redirection, waiting for the child process, etc.

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