Vs2017

src/CommandLineArgumentsParser/Arguments/RegexValueArgument.cs

@@ -11,6 +11,7 @@ namespace CommandLineParser.Arguments
     public class RegexValueArgument : CertifiedValueArgument<string>
     {
         private Regex regex;
+        private string sampleValue;
 
         /// <summary>
         /// Regular expression which the value must match 
@@ -20,6 +21,16 @@ public Regex Regex
             get { return regex; }
             set { regex = value; }
         }
+
+        /// <summary>
+        /// Sample value that would be displayed to the user as a suggestion when 
+        /// the user enters a wrong value. 
+        /// </summary>
+        public string SampleValue
+        {
+            get { return sampleValue; }
+            set { sampleValue = value; }
+        }
 
         #region constructor
 
@@ -78,8 +89,16 @@ protected override void Certify(string value)
             {
                 if (!regex.IsMatch(value))
                 {
-                    throw new CommandLineArgumentOutOfRangeException(
-                        string.Format("Argument '{0}' does not match the regex pattern '{1}'.", value, regex), Name);
+                    if (SampleValue == null)
+                    {
+                        throw new CommandLineArgumentOutOfRangeException(
+                            string.Format("Argument '{0}' does not match the regex pattern '{1}'.", value, regex), Name);
+                    }
+                    else
+                    {
+                        throw new CommandLineArgumentOutOfRangeException(
+                            string.Format("Argument '{0}' does not match the regex pattern '{1}'. An example of a valid value would be '{2}'.", value, regex, SampleValue), Name);
+                    }                    
                 }
             }
         }
@@ -154,6 +173,22 @@ public object DefaultValue
             }
         }
 
+        /// <summary>
+        /// Sample value that would be displayed to the user as a suggestion when 
+        /// the user enters a wrong value. 
+        /// </summary>
+        public string SampleValue
+        {
+            get
+            {
+                return _argumentType.GetPropertyValue<string>("SampleValue", Argument);
+            }
+            set
+            {
+                _argumentType.SetPropertyValue("SampleValue", Argument, value);
+            }
+        }
+
         /// <summary>
         /// When set to true, argument can appear on the command line with or without value, e.g. both is allowed: 
         /// <code>

src/CommandLineArgumentsParser/Arguments/ValueArgument.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Reflection;
@@ -407,15 +408,12 @@ public override void Init()
         public override void PrintValueInfo()
         {
             if (!AllowMultiple)
+            {
                 Console.WriteLine(Messages.EXC_ARG_VALUE_PRINT, Name, _stringValue, _value, typeof(TValue).Name);
+            }
             else
             {
-                string valuesString = String.Empty;
-                foreach (TValue tvalue in _values)
-                {
-                    valuesString += tvalue.ToString();
-
-                }
+                string valuesString = string.Join(", ", _values.Select(v => v.ToString()).ToArray());
                 Console.WriteLine(Messages.EXC_ARG_VALUE_PRINT_MULTIPLE, Name, Values.Count, valuesString, typeof(TValue).Name);
             }
         }

src/CommandLineArgumentsParser/CommandLineArgumentsParser.csproj

@@ -20,7 +20,9 @@
     <GenerateAssemblyProductAttribute>false</GenerateAssemblyProductAttribute>
     <GenerateAssemblyCopyrightAttribute>false</GenerateAssemblyCopyrightAttribute>
     <RootNamespace>CommandLineParser</RootNamespace>
-    <Version>3.0.8</Version>
+    <Version>3.0.8.1</Version>
+    <AssemblyVersion>3.0.8.1</AssemblyVersion>
+    <FileVersion>3.0.8.1</FileVersion>
   </PropertyGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'net20' ">