CommandLine

CommandLine parser

Getting started

First install the package:

Install-Package CommandLine.Net

Then you can define a class that can be used with the parser:

class Options
{
    [RequiredArgument(0,"dir","Directory")]
    public string Directory { get; set; }

    [OptionalArgument("*.*","pattern", "Search pattern")]
    public string SearchPattern { get; set; }
}

This is the code that you need to parse the command line arguments into an object:

if (!Parser.TryParse(args, out Options options))
{
    return;
}

The parser understands common requests for help as you can see below.

Display the available commands

The parser understand the following help commands:

• -? which is the short form help

Usage:
<exename> dir [-pattern value]

For detailed information run '<exename> --help'.

• --help which is the long form help

Usage:
<exename> dir [-pattern value]
 - dir     : Directory (string, required)
 - pattern : Search pattern (string, default=*.*)

Display the help using code

If you want to display the help manually, you can use the Parser.DisplayHelp() API to do it:

Parser.DisplayHelp<Options>();

By default, the API assumes you are using the HelpFormat.Short specifier which maps to /? or -?.

You can ask for the long version of the help by using the HelpFormat.Full specifier:

Parser.DisplayHelp<Options>(HelpFormat.Full);

Specifying multiple enum values

If you have an enum defined as a flags enum, you need to pass this value as an argument in order for it to be correctly parsed: "A, B" or A,B.

[Flags]
enum MyFlags
{
  A = 1,
  B = 2
}

Note:

• The enum values need to be starting at 1, otherwise when the OR operation happens, the value that is 0 will be lost
• The string needs to either be inside a double quote (if it contains a space) or have no space inside

Types of arguments

To use you need to provide a class that is going to hold the options parsed from the command line and use attributes to define the behavior of the parser.

There are 2 kinds of arguments:

• Required
  • These must be specified
  • They have a specific location where they must be specified
• Optional
  • They don't have to be specified
  • They have a name that you need to provide on the command line before you provide the value
  • If they are not specified, the object parsed will have the default value specified.'

Advanced scenarios

Argument grouping

There are cases when you want to have different sets of arguments depending on one of the arguments.

The argument that will be used as the differentiator will be marked with the ActionArgument attribute. That argument must be specified.

You can then define multiple groups of arguments. You will specify the argument group for a property using the ArgumentGroup attribute. A single property in a class can take part in many argument groups.

If a property will be common to all groups, you can use the `CommonArgument' attribute

internal class CommandLineOptions
{
    [ActionArgument]
    public CommandLineActionGroup Action { get; set; }

    [CommonArgument]
    [RequiredArgumentAttribute(0, "host", "The name of the host")]
    public string Host { get; set; }

    #region Add-host Action
    [RequiredArgument(1, "mac", "The MAC address of the host")]
    [ArgumentGroup(nameof(CommandLineActionGroup.add))]
    public string MAC { get; set; }

    #endregion
}

If you have a required argument that is shared between multiple argument groups but use different positions, you can tweak the expected position depending on the group

internal class CommandLineOptions
{
    [ActionArgument]
    public CommandLineActionGroup Action { get; set; }

    // Here the argument 'name' is expected at position 1 in the add group and position 0 in the list group
    [ArgumentGroup(nameof(CommandLineActionGroup.list), 0)]
    [ArgumentGroup(nameof(CommandLineActionGroup.add))]
    [RequiredArgumentAttribute(1, "name", "The name of the host")]
    public string Host { get; set; }

    [ArgumentGroup(nameof(CommandLineActionGroup.add))]
    [RequiredArgumentAttribute(0, "host", "The name of the host")]
    public string Host { get; set; }

}

Argument position override

Sometimes you want to have a common parameter shared across multiple commands, but you want the position of it to be different in those two groups.

To do that, you use the constructor for the ArgumentGroup attribute that takes as the second argument the override position for that argument group.

In the example below, the common parameter repos is defined as required in position 1. For the group Create where no override position is specified, the parameter will be required at position 1. For the group List where the override position is specified, the parameter will be required at position 0.

class OverridePositionGroup
{
    [ActionArgument]
    public Action Action { get; set; }

    [ArgumentGroup(nameof(Action.Create))]
    [RequiredArgument(0, "milestoneInputFile", "The file containing the list of milestones to create.")]
    public string MilestoneFile { get; set; }

    [ArgumentGroup(nameof(Action.List), 0)]
    [ArgumentGroup(nameof(Action.Create))]
    [RequiredArgument(1, "repos", "The list of repositories where to add the milestones to. The format is: owner\\repoName.", true)]
    public List<string> Repositories { get; set; }
}

Background color

The parser will automatically detect the color to use when displaying help in a command prompt. There are a set of colors that are predefined depending on the console color.

You can specify different colors to be used by implementing the IColor interface and configuring the parser:

public class CustomColors : IColors
{
    public ConsoleColor ErrorColor => ConsoleColor.Red;
    public ConsoleColor AssemblyNameColor => ConsoleColor.DarkGray;
    public ConsoleColor ArgumentGroupColor => ConsoleColor.DarkGreen;
    public ConsoleColor RequiredArgumentColor => ConsoleColor.Magenta;
    public ConsoleColor ArgumentValueColor => ConsoleColor.DarkGreen;
    public ConsoleColor OptionalArgumentColor => ConsoleColor.DarkBlue;
}

// Configure the parser to use the new colors
Parser.Configuration.DisplayColors.Set(new CustomColors());

Environment variable parsing

By default, the parser will try and infer optional parameters from the environment variables if they are not specified in the command line.

The order of precedence is going to be (from most specific to least specific):

1. Values passed in via the command line
2. Values specified in the environment
3. Default value specified in the argument type

By default, the Parser will look for environment variables with this name:

CommandLine_<name>

The <name> represents the optional parameter name as defined in the type declaration.

You can change the prefix for the Parser:

ParserOptions parserOptions = new ParserOptions() { VariableNamePrefix = "myPrefix" };

if (!Parser.TryParse(args, out Options options, parserOptions))
{
    return;
}

You can also disable the feature completely:

ParserOptions parserOptions = new ParserOptions() { ReadFromEnvironment = false };

if (!Parser.TryParse(args, out Options options, parserOptions))
{
    return;
}