Pipe text to stdin of running python process

Question

Let's say I have a python script called service.py running as a kind of daemon in the background, and I want to give it some information by piping text into its stdin:

> pgrep -f service.py
[pid of process]
> echo -e 'test\n' > /proc/[pid of process]/fd/0

My python script should take whatever is in its stdin and assign it to a variable inp :

import sys
while True: 
   inp = sys.stdin.readline()
   #do something with inp

But when i do the above, it just prints the stdin stream:

> python service.py 
test            

The effect is the same if I literally just have this in my script

import sys
inp = sys.stdin.readline() #sys.stdin.readline() never returns
                           #script never exits

What am I doing wrong?

Answer 1

you can use named pipe with mkfifo ( https://serverfault.com/questions/443297/write-to-stdin-of-a-running-process-using-pipe )

That leaves you with:

 mkfifo yourfifo cat > yourfifo & mypid=$! yourprogram < yourfifo 

Now you can sent data to your program with

 `echo "Hello World" > yourfifo` 

( https://askubuntu.com/questions/449132/why-use-a-named-pipe-instead-of-a-file )

the key is that stdin has to be known as pipe or named pipe this is why you can use mkfifo , see also How to write data to existing process's STDIN from external process? (python part) and How to write data to existing process's STDIN from external process? (os part)