Implemented escaping expanded environment variables when they are used inside regular expressions.

This fixes #1500.

Duplicati/Library/Utility/Utility.cs

@@ -906,13 +906,40 @@ namespace Duplicati.Library.Utility
         /// <summary>
         /// Expands environment variables, including the tilde character
         /// </summary>
-        /// <returns>The environment variables.</returns>
+        /// <returns>The expanded string.</returns>
         /// <param name="str">The string to expand.</param>
         public static string ExpandEnvironmentVariables(string str)
         {
             return Environment.ExpandEnvironmentVariables(str.Replace("~", HOME_PATH));
         }
 
+        /// <summary>
+        /// Regexp for matching environment variables on Windows (%VAR%)
+        /// </summary>
+        private static readonly Regex ENVIRONMENT_VARIABLE_MATCHER_WINDOWS = new Regex(@"\%(?<name>\w+)\%");
+
+        /// <summary>
+        /// Regexp for matching environment variables on Linux ($VAR or ${VAR})
+        /// </summary>
+        private static readonly Regex ENVIRONMENT_VARIABLE_MATCHER_LINUX = new Regex(@"\$(?<name>\w+)|(\{(?<name>[^\}]+)\})");
+
+        /// <summary>
+        /// Expands environment variables, including the tilde character, in a RegExp safe format
+        /// </summary>
+        /// <returns>The expanded string.</returns>
+        /// <param name="str">The string to expand.</param>
+        public static string ExpandEnvironmentVariablesRegexp(string str)
+        {
+            return
+
+                // TODO: Should we switch to using the native format, instead of following the Windows scheme?
+                //IsClientLinux ? ENVIRONMENT_VARIABLE_MATCHER_LINUX : ENVIRONMENT_VARIABLE_MATCHER_WINDOWS
+
+                ENVIRONMENT_VARIABLE_MATCHER_WINDOWS
+                    .Replace(str.Replace("~", Regex.Escape(HOME_PATH)), (m) => 
+                        Regex.Escape(Environment.GetEnvironmentVariable(m.Groups["name"].Value)));
+        }
+
         /// <summary>
         /// Checks that a hostname is valid
         /// </summary>

Duplicati/Server/Runner.cs

@@ -654,7 +654,7 @@ namespace Duplicati.Server
             
             return options;
         }
-        
+
         private static Duplicati.Library.Utility.IFilter ApplyFilter(Duplicati.Server.Serialization.Interface.IBackup backup, DuplicatiOperation mode, Duplicati.Library.Utility.IFilter filter)
         {
             var f2 = backup.Filters;
@@ -662,7 +662,10 @@ namespace Duplicati.Server
             {
                 var nf =
                     (from n in f2
-                    let exp = Library.Utility.Utility.ExpandEnvironmentVariables(n.Expression)
+                    let exp = 
+                        n.Expression.StartsWith("[") && n.Expression.EndsWith("]")
+                        ? Library.Utility.Utility.ExpandEnvironmentVariablesRegexp(n.Expression)
+                        : Library.Utility.Utility.ExpandEnvironmentVariables(n.Expression)
                     orderby n.Order
                     select (Duplicati.Library.Utility.IFilter)(new Duplicati.Library.Utility.FilterExpression(exp, n.Include)))
                     .Aggregate((a, b) => Duplicati.Library.Utility.FilterExpression.Combine(a, b));