getopt helpWanted

[wobbles via Digitalmars-d-learn]

On Wednesday, 29 April 2015 at 22:02:29 UTC, novice2 wrote:
> Hello.
>
> Help me please to understand, how to show usage help to user, 
> who enter wrong options?
> For example, user not provided required filename.
> I want to show error message, and program usage help text.
> But likely getopt don't provide help text until valid options 
> will be parsed.
>
> Reduced code:
> ///////////////
> import std.stdio: writefln;
> import std.getopt;
>
> void main (string[] args)
> {
>   string fname;
>   GetoptResult helpInfo;
>
>   try
>   {
>     helpInfo = getopt(
>       args,
>       std.getopt.config.required, "file|f", "File name", 
> &fname);
>
>     writefln("Options parsed: fname=%s", fname);
>   }
>   catch(Exception e)
>   {
>     writefln("\nERROR: %s", e.msg);
>     defaultGetoptPrinter("Program usage:", helpInfo.options);
>   }
> }
> ///////////////
>
> Output:
> ERROR: Required option file|fwas not supplied
> Program usage:

Also, I suggest you look at docopt:
http://code.dlang.org/packages/docopt

It makes the whole parsing of CLI arguments very nice and easy.