如何从子处理的python脚本打印到终端窗口

Question

I create a subprocess running a python script like this:

p = subprocess.Popen(['nohup', 'python', 'listen.py'],
                     cwd="/execute",
                     stdout=subprocess.PIPE,
                     stderr=subprocess.STDOUT)

I then let the spawning thread terminate; and the spawned subprocess remains running. The user (me) is back at the bash terminal.

I wish to print to this terminal from within the subprocess (from listen.py) - how can I achieve this?

Answer 1

With nohup , you simply can't. One of the features of nohup is that it detaches the started process from any terminal.

Without nohup , in the trivial case, simply don't use the stdin , stdout , or stderr keyword arguments to Popen() at all; the subprocess will inherit copies of these file descriptors from the calling process.

Having a background process write to your terminal while you are using it can be extremely disruptive, though; a better solution is usually to have the process write to a log file, which you can tail -f if you want to, in a different terminal or another program if you like.

Answer 2

So script A spawns script B and terminates, and then you want to access the stdout of script B?

The first thing is that you probably don't want to capture the stdout from script B in A. But the stdout has to go somewhere, such as to a file (solution 2) or it can just be inherited stdout from the parent process (solution 1).

Solution 1

The following will exit to the shell immediately then write "123" to the same terminal 3 seconds later. If you pipe script A to a file then the outputs of script B will go there too.

python -c "import subprocess; subprocess.Popen(['python', '-c', 'import time; time.sleep(3); print(123)'])"

Solution 2

If you want script A to output to the terminal, but for script B's output to be stored somewhere else then you can write it to a file directly, such as by providing the file as the stdout kwarg to Popen like so:

p = subprocess.Popen(['python', 'listen.py'],
                     cwd="/execute",
                     stdout=open('/execute/results.txt', 'w'),
                     stderr=subprocess.STDOUT)

Solution 3

Or if you specifically want to use nohup then the following will by usually default write the output from the subprocess to nohup.txt

p = subprocess.Popen(['nohup', 'python', 'listen.py'],
                     cwd="/execute",
                     stderr=subprocess.STDOUT)