Theoreticly, if I know the pid of the bash shell which is running, I can run a cat whose stdout is redirected to the stdin of that shell. It seems to be as if I type something on that shell. Unfortunately, there WILL be stream coming from cat, BUT WILL NOT make the shell act properly (the entered command from cat will not be executed by bash).

Open a terminal:

```
ps -ef | grep bash
ymf       4906  4887  0 16:19 pts/0    00:00:00 /bin/bash

```

On another terminal:

```
cat 1> /proc/4906/fd/0
echo 'hello!'

```

Why?