+pushvar(){
+ for var in $*; do
+ eval level=\${${var}_level:=0}
+ eval ${var}_${level}="\$$var"
+ eval ${var}_level=$(($level+1))
+ done
+}
+
+popvar(){
+ for var in $*; do
+ eval level=\${${var}_level:-0}
+ test $level = 0 && continue
+ eval level=$(($level-1))
+ eval $var="\${${var}_${level}}"
+ eval ${var}_level=$level
+ eval unset ${var}_${level}
+ done
+}
+