env variables ?

Hi,

What about the env variables in Haiku ?

Is there someting to get more clean programs ? :
Something that can replace (the first line into scripts) :
#!/boot/home/config/bin/perl
by something like :
#!$APP/perl

What about using the XDG vars from Linux :
http://www.freedesktop.org/wiki/Software/xdg-user-dirs