PROJECT_JRUBY_OPTS=( --1.9 )

[[ -s "$HOME/.rvm/scripts/rvm" ]] && . "$HOME/.rvm/scripts/rvm" # This loads RVM into a shell session.

$ JRUBY_OPTS=--1.9 jruby -v
jruby 1.6.5 (ruby-1.9.2-p136) (2011-10-25 9dcd388) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_27) [darwin-x86_64-java]

$ export JRUBY_OPTS=--1.9
$ jruby -v
jruby 1.6.5 (ruby-1.8.7-p330) (2011-10-25 9dcd388) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_27) [darwin-x86_64-java]
$ env | grep JRUBY_OPTS
[empty result]

rvm get head
chmod +x ${rvm_path}/hooks/after_use_jruby_opts

export JRUBY_OPTS="--1.9 -J-XX:+CMSClassUnloadingEnabled -J-XX:+UseConcMarkSweepGC -J-XX:MaxPermSize=256m -J-Xmx1024m"

$ jruby -v
jruby 1.6.5 (ruby-1.9.2-p136) (2011-10-25 9dcd388) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_29) [darwin-x86_64-java]

$ cat >> ~/tmp/.rvmrc
export JRUBY_OPTS='--1.9'
^D

$ cd ~/tmp
$ env | grep OPTS
JRUBY_OPTS='--1.9'

$ chmod +x ${rvm_path}/hooks/after_use_jruby_opts # or after_use_jruby

$ cd ~/tmp
$ rvm --rvmrc --create jruby@projectxyz # edit the resulting .rvmrc, uncomment PROJECT_JRUBY_OPTS

$ cd ~/tmp
$ env | grep OPTS
JRUBY_OPTS='--1.9'

export JRUBY_OPTS=--1.9

JRUBY_OPTS=-Xcext.enabled=true