CLI API

CLI is a template that provides entry-point functions to call argparse.

Here are the signatures that CLI template has:

template CLI(Config config, COMMAND)
template CLI(Config config, COMMANDS...)

The second template with multiple COMMANDS... has only main function which wraps all COMMANDS inside internal struct with only data member of type SubCommand!COMMANDS and calls CLI(Config config, CMD).main with that.

There is also an alias that uses default Config.init to simplify default behavior:

alias CLI(COMMANDS...) = CLI!(Config.init, COMMANDS);

Public members

parseKnownArgs

CLI.parseKnownArgs is a function that parses only known arguments from the command line.

All arguments that were not recognized during parsing are returned to a caller.

Signature

Result parseKnownArgs(ref COMMAND receiver, string[] args, out string[] unrecognizedArgs)
Result parseKnownArgs(ref COMMAND receiver, ref string[] args)

Parameters

receiver
Object that receives parsed command line arguments.
args
Command line arguments to parse (excluding argv[0] – first command line argument in main function).
unrecognizedArgs
Command line arguments that were not parsed.

Notes

The second signature (without unrecognizedArgs parameter) returns not parsed arguments through args reference parameter.

Return value

Result object that can be cast to bool to check whether the parsing was successful or not. Successful parsing for parseKnownArgs function means that there are no error during parsing of known arguments. This means that having unrecognized arguments in a command line is not an error.

parseArgs

CLI.parseArgs is a function that parses command line arguments and validates that there are no unknown ones.

Signature

Result parseArgs(ref COMMAND receiver, string[] args)

Parameters

receiver
Object that receives parsed command line arguments.
args
Command line arguments to parse (excluding argv[0] – first command line argument in main function).

Return value

In case of parsing error - Result.exitCode (1 by default).
In case of success - 0.

complete

CLI.complete is a function that performs shell completion for command line arguments.

Signature

int complete()(string[] args)

Parameters

args
Command line arguments (excluding argv[0] – first command line argument in main function).

Notes

This function provides completion for the last argument in the command line:

If the last entry in command line is an empty string ("") then it provides all available argument names prepended with Config.shortNamePrefix or Config.longNamePrefix.
If the last entry in command line contains characters then complete provides completion only with those arguments that have names starting with specified characters.

Return value

0 in case of successful parsing.
Non-zero otherwise.

mainComplete

CLI.mainComplete is a mixin template that provides global main function which calls CLI.complete.

Signature

template mainComplete()

Notes

Ingested main function is a simple wrapper of CLI.complete function that removes argv[0] from command line.

Return value

Value returned from CLI.complete function.

main

CLI.main is a mixin template that does one of these:

If argparse_completion version is defined then it instantiates CLI.mainComplete template mixin.
Otherwise it provides global main function that calls CLI.parseArgs function.

Signature

template main(alias newMain)

Parameters

newMain
Function that is called after successful command line parsing. See newMain for details.

Notes

newMain parameter is not used in case if argparse_completion version is defined.

Return value

See CLI.mainComplete and CLI.parseArgs.

newMain parameter

newMain parameter in CLI API is a substitution for classic main function with the following differences:

Its first parameter has type of a command struct that is passed to CLI API. This parameter is filled with the data parsed from actual command line.
... newMain(COMMAND command)
It might have optional second parameter of type string[] that receives unknown command line arguments.
... newMain(COMMAND command, string[] unrecognizedArgs)
newMain can optionally return int value. In this case, argparse will return that value from main function.

Last modified: 24 October 2025