Source my bash profile when I su on OS X

Question

I'd like to source my .bash_profile (or maybe some other file) whenever I switch to superuser. (.bash_profile is the login rc on Mac OS X, .bashrc is the non-login script, and .profile is a login rc that runs for any shell).

Simply, my .bash_profile makes using a terminal more convenient for me, and on those occasional times when I have to go super, I feel like I'm trying to play a guitar without thumbs. More than that, $PS1 and $PROMPT_COMMAND get exported to the super user, but functions defined in my .bash_profile and used in my $PROMPT_COMMAND do not get exported to that lexical environment.

In particular, I source the git-prompt.sh script in my .bash_profile and use the exported __git_ps1 command in my $PROMPT_COMMAND. Thus, every single prompt line in the superuser shell is preceded by the warning:

bash: __git_ps1: command not found.

Now I technically could modify the system-wide rc in /etc/profile in order to achieve the effect. I could look at $HOME, and if it's my home, then source $HOME/.bash_profile. However, this isn't portable. I would have to modify the /etc/profile on every host in which I'm likely to be working. I want to export this behavior to happen on all hosts on which I work.

Can anyone think of a solution that is completely contained in my own bash profile?

No warnings about becoming a super user are necessary. I know there's sudo, and that it's bad, bad, bad, and I'm morally and intellectually inferior for doing it. :)

Mac OS X's su doesn't have the -c option, which would have been a pretty good solution.

Answer 1

Alright. I have something now. It's not pretty, but it does work. The main trick is that I can cause code to be executed in the super user shell by changing $PROMPT_COMMAND in the environment. $PROMPT_COMMAND gets executed right away when switching to the new environment, and su preserves bash environment variables.

Thus, here is the solution I'm using:

alias su="export REAL_HOME=$HOME && export SWITCHING_TO_SU=true && export PROMPT_COMMAND='source $HOME/.bash_profile; $PROMPT_COMMAND' && su"

Now my .bash_profile will be run as soon as I switch to the super user, and it will know two key pieces of information: 1) that it is being run because I am switching to super user, and 2) the location of my real home directory. It can use that information to do anything else it needs to do. In particular, my .bash_profile will reset $PROMPT_COMMAND back to its true value, so that the script gets sourced only when switching to su. At the end of the script, I have

if [[ "$SWITCHING_TO_SU" == 'true' ]]; then
    unset SWITCHING_TO_SU
    unset REAL_HOME
fi

A similar trick based on aliasing exit() could be used, I believe, to do something when switching out of super user.

Answer 2

If you su from your $HOME, you could just do

. .bash_profile