Hello

I'm trying to get getopt to recognize an argument that may or may not take a value. Here's an example :

./hashtrack --list
./hashtrack --list filter

The problem is that if I point list to a string variable, the first call fails with "Missing value for argument --list".

I tried having it point to a callback with an optional second parameter :

void cb(string option, string value = "")
{
    writeln("--list");
    option.writeln();
    value.writeln();
}

But I get the same error. I also tried having two callbacks with the same name. The first one takes a single argument, and the second one accepts two :

void cb(string option)
{
    writeln("--list");
    option.writeln();
}

void cb(string option, string value)
{
    writeln("--list");
    option.writeln();
    value.writeln();
}

But it only calls the first one. I'm using DMD64 D Compiler v2.090.0. Any pointers ?

On 8/8/20 7:58 PM, Hassan wrote:
> Hello
> 
> I'm trying to get getopt to recognize an argument that may or may not take a value. Here's an example :
> 
> ../hashtrack --list
> ../hashtrack --list filter
> 
> The problem is that if I point list to a string variable, the first call fails with "Missing value for argument --list".
> 
> I tried having it point to a callback with an optional second parameter :
> 
> void cb(string option, string value = "")
> {
>      writeln("--list");
>      option.writeln();
>      value.writeln();
> }
> 
> But I get the same error. I also tried having two callbacks with the same name. The first one takes a single argument, and the second one accepts two :
> 
> void cb(string option)
> {
>      writeln("--list");
>      option.writeln();
> }
> 
> void cb(string option, string value)
> {
>      writeln("--list");
>      option.writeln();
>      value.writeln();
> }
> 
> But it only calls the first one. I'm using DMD64 D Compiler v2.090.0. Any pointers ?

getopt doesn't support optional parameters.

Two things I can think of:

1. Have 2 options that do the same thing, but only one accepts a parameter (e.g. `--list` and `--listf filter`)
2. If your optional parameters are not tied to the option itself, then don't accept them via getopt. In other words, if `hashtrack filter` is supposed to be valid, then filter isn't an option after all, it's a standard parameter.

-Steve

Thanks for the reply Steve

On Sunday, 9 August 2020 at 12:20:16 UTC, Steven Schveighoffer wrote:
> 2. If your optional parameters are not tied to the option itself, then don't accept them via getopt. In other words, if `hashtrack filter` is supposed to be valid, then filter isn't an option after all, it's a standard parameter.

"filter" can be any string really. It's like an input to the list option : hashtrack --list filter_by_this_word

I wasn't aware that there was a distinction between parameters and options. The tool I'm writing is a D port of an existing Go command line utility that uses parameters everywhere, things like "hashtrack list" instead of "hashtrack --list". I decided to use options as opposed to parameters because then I would get to use getopt to handle "args" and display a nicely formatted --help output.

I decided to go with this second solution even though "hashtrack filter" isn't technically valid. Here's what I did :

void main()
{
    //....
    bool list;

    auto opts = args.getopt(
        "login", "Creates a session token and store it in the local filesystem in a config file", &login,
        "logout", "Remove the locally stored session token", &logout,
        "track", "Tracks one or more hashtags", &track,
        "untrack", "Untracks one or more previously tracked hashtags", &untrack,
        "tracks", "Displays the hashtags you are tracking", &tracks,
        "list", "Displays the latest 50 captured tweets", &list,
        "watch", "Stream and display the captured tweets in real-time", &watch,
        "status", "Displays who you are, if logged in", &status,
        "endpoint", "Point to another server", &endpoint,
        "config", "Load a custom config file", &config
    );
    //....
    if(list)
    {
        string filter = args.length > 1 ? args[1] : "";
        tracking.list(filter).each!writeln;
    }
}