+# check which of the given packages are installed
+grep_installed () {
+ local package installed
+
+ for package in $*; do
+ if pkg $package; then
+ installed="$installed $package"
+ fi
+ done
+
+ echo $installed
+}
+
+# only upgrade packages if they are already installed
+pkgadd_if_installed () {
+ local packages
+
+ packages=$( grep_installed $* )
+
+ if [ "$packages" ]; then
+ eval pkgadd $packages
+ fi
+}
+