Correctly hilight variables

lib/ace/mode/sh_highlight_rules.js

@@ -73,6 +73,10 @@ var ShHighlightRules = function() {
     var floatNumber = "(?:" + exponentFloat + "|" + pointFloat + ")";
     var fileDescriptor = "(?:&" + intPart + ")";
 
+    var variableName = "[a-zA-Z][a-zA-Z0-9_]*";
+
+    var variable = "(?:(?:\\$" + variableName + ")|(?:" + variableName + "=))";
+
     this.$rules = {
         "start" : [ {
             token : "comment",
@@ -80,6 +84,9 @@ var ShHighlightRules = function() {
         }, {
             token : "string",           // " string
             regex : '"(?:[^\\\\]|\\\\.)*?"'
+        }, {
+            token : "variable",
+            regex : variable
         }, {
             token : "support.function",
             regex : fileDescriptor