Hi I am trying to use a Unix FIFO to communicate between a Python script and a shell script. The intention is for the shell script to capture all output of the python script. So far I have the following:
#!/bin/bash # Test IPC using FIFOs. ## Create a named pipe (FIFO). mkfifo ./myfifo ## Launch the Python script asynchronously and re-direct its output to the FIFO. python3 helloworld.py > ./myfifo & PID_PY=$! echo "Python script (PID=$PID_PY) launched." ## Read from the FIFO using cat asynchronously. ## Note that running asynchronously using & runs it the program (in this case `cat`) ## in a child shell "subshell", so I will collect the output in a file. echo "Reading FIFO." >output.log cat ./myfifo & PID_CAT=$! ## Sleep for 10 seconds. sleep 10 ## Kill the Python script. kill -15 $PID_PY && echo "Python script (PID=$PID_PY) killed." ## Kill the cat! kill -15 $PID_CAT ## Remove the pipe when done. rm -fv ./myfifo ## Check for the existence of the output log file and print it. [[ -f output.log ]] && cat output.log || echo "No logfile found!." 1>&2 However when I open the log file output.log, it is empty which is why the last command returns empty. Is there something I am doing wrong. I understand the above might be easily accomplished using an anonymous pipe like so: python3 helloworld.py | cat >output.log (or even python3 helloworld.py > output.log for that matter) but my intention is to understand the use of named pipes in Unix/Linux.
The python script just prints something to stdout every 1 second:
if __name__ == "__main__": import time try: while True: print("Hello, World") time.sleep(1) except KeyboardInterrupt: print('Exiting.') finally: pass 
