The danger of just trusting the cat command

cat-danger.py

#!/usr/bin/env python3
hidden_cmd = "echo 'You forgot to check `cat -A`!' > oops"
visible_cmd = "echo 'Hello world!'"
if __name__ == "__main__":
    with open("demo.sh", "w") as f:
        txt = "#!/bin/sh\n"
        txt += hidden_cmd + ";" + visible_cmd + " #\r" + visible_cmd + " " * (len(hidden_cmd) + 3) + "\n"
        f.write(txt)