Useful gfsh Shell Variables says gfsh>echo --string=${VARIABLE}
could obtain the current value of the existing variable. But in my environment it couldn't.
e.g.:
echo --string=${SYS_USER}
displayed ${SYS_USER}
gfsh>echo --string=$*
could display a list of all gfsh shell variables and their current values in my environment(Apache Geode 1.5.0).