Help generation

Command

Command UDA provides few customizations that affect help text. It can be used for top-level command and subcommands.

Program name (i.e., the name of top-level command) and subcommand name can be provided to Command UDA as a parameter. If program name is not provided, then Runtime.args[0] (a.k.a. argv[0] from main function) is used. If subcommand name is not provided (e.g., @(Command.Description(...))), then the name of the type that represents the command is used.
Usage – allows custom usage text. By default, the parser calculates the usage message from the arguments it contains but this can be overridden with Usage call. If the custom text contains %(PROG) then it will be replaced by the command/program name.
Description – used to provide a description of what the command/program does and how it works. In help messages, the description is displayed between the usage string and the list of the command arguments.
ShortDescription – used to provide a brief description of what the subcommand does. It is applicable to subcommands only and is displayed in Available commands section on help screen of the parent command.
Epilog – custom text that is printed after the list of the arguments.

Usage, Description, ShortDescription and Epilog modifiers take either string or string function() value – the latter can be used to return a value that is not known at compile time.

Argument

There are some customizations supported on argument level for both PositionalArgument and NamedArgument UDAs:

Description – provides brief description of the argument. This text is printed next to the argument in the argument-list section of a help message. Description takes either string or string function() value – the latter can be used to return a value that is not known at compile time.
HideFromHelp – can be used to indicate that the argument shouldn’t be printed in help message.
Placeholder – provides custom text that is used to indicate the value of the argument in help message.

Help text styling

argparse uses Config.styling to determine what style should be applied to different parts of the help text. Please refer to ANSI coloring and styling section for details.

Example

Here is an example of how this customization can be used:

import argparse;

@(Command("MYPROG")
.Description("custom description")
.Epilog("custom epilog")
)
struct T
{
    @NamedArgument  string s;
    @(NamedArgument.Placeholder("VALUE"))  string p;

    @(NamedArgument.HideFromHelp)  string hidden;

    enum Fruit { apple, pear };
    @(NamedArgument("f","fruit").Required.Description("This is a help text for fruit. Very very very very very very very very very very very very very very very very very very very long text")) Fruit f;

    @(NamedArgument.AllowedValues!([1,4,16,8])) int i;

    @(PositionalArgument(0).Description("This is a help text for param0. Very very very very very very very very very very very very very very very very very very very long text")) string param0;
    @(PositionalArgument(1).AllowedValues!(["q","a"])) string param1;
}

T t;
CLI!T.parseArgs(t, ["-h"]);

This example will print the following help message:

Argument groups

By default, parser groups command line arguments into “required arguments” and “optional arguments” when displaying help message. When there is a better conceptual grouping of arguments than this default one, appropriate groups can be created using ArgumentGroup UDA.

This UDA has some customization for displaying help text:

Description – provides brief description of the group. This text is printed right after group name. It takes either string or string function() value – the latter can be used to return a value that is not known at compile time.

Example:

import argparse;

@(Command("MYPROG")
.Description("custom description")
.Epilog("custom epilog")
)
struct T
{
    @(ArgumentGroup("group1").Description("group1 description"))
    {
        @NamedArgument
        {
            string a;
            string b;
        }
        @PositionalArgument(0) string p;
    }

    @(ArgumentGroup("group2").Description("group2 description"))
    @NamedArgument
    {
        string c;
        string d;
    }
    @PositionalArgument(1) string q;
}

T t;
CLI!T.parseArgs(t, ["-h"]);

When an argument is attributed with a group, the parser treats it just like a normal argument, but displays the argument in a separate group for help messages:

Last modified: 07 August 2024