[galaxy-dev] Environmental Variable in <version_command>

Is it possible to use environment variables within <version_command>? I'm trying to use git commit information as the version ID in galaxy where the path $GITREPO can change: e.g. <version_command>git --git-dir="$GITREPO/project.git" log -n 1 origin/master | grep -P "commit|Author|Date"</version_command> Thanks!