switching a context

[Une Bévue <yt.dev@xxxxxxx>]

On my bow i do have to installation of ruby

one under /opt/local

another under ~/


the first is the standard ruby the second is another version of ruby  
callable by java thru jRuby.

they have in common some names of env vars :

as for example GEM_HOME but they do not have to point to the same  
directory.

they have also in common names of scripts.

here it is esier to make the differnce

when i have "gem" for the first ruby i use jgem for jRuby by aliasing :

alias jgem="$JRUBY_HOME/jruby $JRUBY_BIN/gem"

then, the question is, when i use such an alias may i have a way to  
switch the context, that's to say :

instead of having $GEM_HOME=/opt/local...

having $GEM_HOME=~/...

is that possible using zsh ?

Yvon