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C#/.NET Command Line Argument Parser Reloaded

, 9 Jul 2014 CPOL
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Easy to use yet powerful command line argument parser which also creates usage and parameter information for the user.


Many programs use command line arguments. Each time parsing has to be done in the same way. There are other projects which facilitate the parsing process. For example, C#/.NET Command Line Arguments Parser does a great job, however it lacks verification of the passed and parsed arguments. C# command-line option parser can do that, however using it is quite complicated. CLAParser is a compromise of both: It is easy to use and uses regular expressions for parsing and validating which makes it quite powerful. Further more, it supports i18n and it creates information for correct command line usage for the user.

Naming Conventions

  • Arguments: Everything passed on argument line to program separated by spaces, or grouped by quotes, e.g.
    program.exe argument1 /argument2 
    	--argument3 .!§$argument4´ß2! "argument5 with spaces"
  • Parameter: All arguments that start with / or -, e.g.
    program.exe /parameter1 -parameter2
  • Values: Every argument that is not a parameter, e.g.
    program.exe value1 value2 /my_param  'v a l u e 3'

In the last example, value1 and value2 are values without parameters, whereas v a l u e 3 belongs to parameter my_param. (Note that the single quotes which hold 'v a l u e 3' together are removed by CLAParser.)

Using the Code

  1. Copy CLAParser files to your project folder and include them in C# project (CmdLineArgumentParser.cs, CmdLineArgumentParserRes.resx, and optionally further resx-files).

    project explorer

  2. Create a CLAParser instance by calling the constructor.
    CLAParser.CLAParser CmdLine = new CLAParser.CLAParser("CLAParserTest");
    The argument must be the default namespace. (This is necessary so that CLAParser can find its resx-files.)
  3. Use CmdLine.Parameter() function to define known parameters.
        "", CLAParser.CLAParser.ValueType.String,
        "Path to file that is to be loaded on starting the program.");
        "output", CLAParser.CLAParser.ValueType.OptionalString,
        "Write output to file, if no file specified default file output.txt is used.");
    CmdLine.Parameter(CLAParser.CLAParser.ParamAllowType.Required, "add",
        "Do a mathematical addition of number given integers.");
  4. Start parsing by calling function CmdLine.Parse(). Raised exceptions can be passed directly to the user. They indicate the reason for the problem. Further, show user correct syntax and information about the parameters using CmdLine.GetUsage() and CmdLine.GetParameterInfo().
    catch (CLAParser.CLAParser.CmdLineArgumentException Ex)
  5. If arguments are correct and all required arguments are defined, no exception is raised and values of all parameters can be accessed by the dictionary interface. Optional parameters which are not defined by the user are indicated by null values. A value without parameter can be accessed by the empty string ("").
    if(CmdLine[""] != null)
        value = CmdLine[""];
    if(CmdLine["parameter"] != null)
        value = CmdLine["parameter"];

Points of Interest

  • Update: Using the obsolete function Parse(string[] Arguments) with args as parameter quotes (") must be escaped (\") to be recognized correctly. It is recommended to use function Parse() instead!
  • Function FindMismatchReasonInRegex() helps in analyzing why a search string does not match a regular expression and indicates where the problem probably is located.
  • CLAParser is internationalized, i.e. new languages can easily be defined by creating new resx-files (localization).
  • Using the enumerator, all arguments can be traversed, e.g.:
    IEnumerator e = CmdLine.GetEnumerator();
    while (e.MoveNext())
        DictionaryEntry arg = (DictionaryEntry)e.Current;
        Console.WriteLine(arg.Key + "=" + arg.Value);
  • For a complete overview of CLAParser's capabilities, have a look at the attached code files.


  • 2010-02-24
    • Initial release
  • 2010-04-05
    • CmdLineArgumentParser.cs:574 -> from "...Parameters == false)" to "...Parameters == true)"
  • 2011-01-06
    • Corrected error in regular expression which made it impossible to use more than one quoted value
    • Added internal function GetRawCommandlineArgs() proposed by vermis0. Together with it comes function Parse() which makes function Parse(string[] Arguments) obsolete. Now the quotes of quoted values (e.g. "value with spaces") do not need to be escaped anymore!
  • 2011-01-07
    • Corrected error in regular expression which made it impossible to use a value without parameter containing minus (-) or slash (/).
    • Made behaviour with (first) value without parameter more consistent. Instead of setting AllowValuesWithoutParameter, use function Parameter() with ParameterName=="".
    • Fixed error with case sensitivity of parameter. Now everything is case insensitive.
  • 2011-09-09
    • Corrected problem reported by Hautzendorfer concerning single parameters not being processed correctly
  • 2014-07-09
    • Corrected problem reported by Gray John concerning multiple boolean parameters not being processed correctly


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Julian Ohrt

United States United States
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Comments and Discussions

BugProblem with multiple Bool parms PinmemberGray John5-Mar-14 9:58 
AnswerRe: Problem with multiple Bool parms PinmemberJulian Ohrt9-Jul-14 5:12 
SuggestionSimple Command Line Arguments Parser PinmemberMember 14778522-Mar-12 6:31 
QuestionSomething more Functional PinmemberAlois Kraus9-Sep-11 13:26 
AnswerRe: Something more Functional PinmemberJulian Ohrt10-Sep-11 0:47 
GeneralRe: Something more Functional PinmemberAlois Kraus10-Sep-11 0:58 
GeneralIsn't there a problem ... PinmemberHautzendorfer23-May-11 10:54 
AnswerRe: Isn't there a problem ... PinmemberJulian Ohrt9-Sep-11 3:55 
QuestionFxCop Compliance PinmemberDave Hary8-Jan-11 9:13 
AnswerRe: FxCop Compliance Pinmemberleppie10-Jan-11 0:04 
GeneralRe: FxCop Compliance PinprofessionalPIEBALDconsult21-Sep-13 11:04 
AnswerRe: FxCop Compliance PinmemberJulian Ohrt9-Sep-11 3:59 
GeneralSuggestion on using Environment.CommandLine Pinmembervermis06-Dec-10 10:53 
GeneralRe: Suggestion on using Environment.CommandLine PinmemberHeinz JKarl Otta Fritz6-Jan-11 4:11 
GeneralWorks great Pinmemberssm629716-Jul-10 7:21 
QuestionWhat about... Pinmemberkornman005-Mar-10 6:40 
AnswerRe: What about... PinmemberMarkLTX5-Mar-10 7:33 
GeneralRe: What about... Pinmemberkornman005-Mar-10 8:16 
GeneralRe: What about... PinmemberHeinz JKarl Otta Fritz5-Apr-10 4:09 
GeneralI like what you have done, but alas someone beat you to it PinmvpSacha Barber5-Mar-10 2:18 
GeneralRe: I like what you have done, but alas someone beat you to it PinmemberHeinz JKarl Otta Fritz5-Apr-10 4:16 

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