I want to pass stdin to a bash script to an python script called in that bash script

Question

I've a bash script invoking a python script I want to feed the content of file via stdin. Calling the bash script like:

./script.sh < file

And the contents of script.sh:

#! /usr/bin/env bash
pushd /some/python/virtual/environment/working/dir
source venv/bin/activate
python main.py ??????
deactivate
popd

I've no idea what to fill in for ?????? to pass the contents of file given to the bash script as stdin to the python script main.py.

Note that file can be a substantial text file and using bash's read is not desirable.

Using stdin when invoking the bash script is a requirement. I'm flexible to pass whatever to main.py.

Any ideas out there how to tackle this conundrum?

addition

The answer by @cas made it clear to me that I also need to explain in which context I try to use script.sh.

I want to use script.sh as a forwarding script in ~/.forward, with the contents:

|/path/to/script.sh

Which postfix does call as /path/to/script.sh; the log is clear about that. A simple test using a dressed down version of the python script, like:

|/path/to/simple/main.py

Demonstrates that postfix does call main.py with the content of the mail on the stdin. But the combination doesn't seem to work.

Answer 1

Assuming that your main.py script is correctly written to read from stdin and that nothing in venv/bin/activate reads from stdin(*), ?????? should be "nothing at all".

There are no previous commands in the bash script that will consume stdin before python, so python will just start consuming it.

#/bin/bash
pushd /some/python/virtual/environment/working/dir
source venv/bin/activate
python main.py
deactivate

Or make main.py executable and run it directly as ./main.py...works the same, either way.

(*) if there was, you probably wouldn't be able to do this at all, without something ugly like capturing all of stdin to a variable and then piping or <<< redirecting the variable into first venv/bin/activate and then main.py.

---

For a very obvious example of what is happening here and why this works, consider the following sh script kitten.sh:

#!/bin/sh
cat

It just runs cat, which begins reading from stdin and printing its input to stdout.