functions.sh: add list_contains function for checking whether a list contains a specific element

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@12025 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/base-files/files/etc/functions.sh

@@ -24,6 +24,15 @@ append() {
 	eval "export ${NO_EXPORT:+-n} -- \"$var=\${$var:+\${$var}\${value:+\$sep}}\$value\""
 }
 
+list_contains() {
+	local var="$1"
+	local str="$2"
+	local val
+
+	eval "val=\" \${$var} \""
+	[ "${val%% $str *}" != "$val" ]
+}
+
 list_remove() {
 	local var="$1"
 	local remove="$2"