Wrap all commands entered within a Bash-Shell with a Python script

Question

What i'd like to have is a mechanism that all commands i enter on a Bash-Terminal are wrapped by a Python-script. The Python-script executes the entered command, but it adds some additional magic (for example setting "dynamic" environment variables). Is that possible somehow?

I'm running Ubuntu and Debian Squeezy.

Additional explanation:

I have a property-file which changes dynamically (some scripts do alter it at any time). I need the properties from that file as environment variables in all my shell scripts. Of course i could parse the property-file somehow from shell, but i prefer using an object-oriented style for that (especially for writing), as it can be done with Python (and ConfigObject).

Therefore i want to wrap all my scripts with that Python script (without having to modify the scripts themselves) which handles these properties down to all Shell-scripts. This is my current use case, but i can imagine that i'll find additional cases to which i can extend my wrapper later on.

Answer 1

The perfect way to wrap every command that is typed into a Bash Shell is to change the variable PROMPT_COMMAND inside the .bashrc. For example, if I want to do some Python stuff before every command, liked asked in my question:

.bashrc:

# ...
PROMPT_COMMAND="python mycoolscript.py; $PROMPT_COMMAND;"
export $PROMPT_COMMAND
# ...

now before every command the script mycoolscript.py is run.

Answer 2

Use Bash's DEBUG trap. Let me know if you need me to elaborate.

Edit:

Here's a simple example of the kinds of things you might be able to do:

$ cat prefix.py
#!/usr/bin/env python
print "export prop1=foobar"
print "export prop2=bazinga"
$ cat propscript
#!/bin/bash
echo $prop1
echo $prop2
$ trap 'eval "$(prefix.py)"' DEBUG
$ ./propscript
foobar
bazinga

You should be aware of the security risks of using eval.