Is it possible to take an argument as both positional and by flag?

[casey]

I have a clap CLI where it's possible to do the following:

foo --input bar

But I'd like to also allow the following:

foo bar

Without breaking the first usage.

Is that possible? I think that perhaps I can do it by by defining two input arguments, one positional and one taken with --inptut, and making exactly one required, but I think that might make the help message a bit more confusing.

[pksunkara]

What you wrote is correct. We don't have any other way to do it.

[casey]

Ahh, gotcha. Thanks for the info! It might be a good feature, since it's enables conservative CLI design. (I.e. creating long flags at first, and then later promoting to short, and then positional, depending on which flags are most used and useful.) I just opened #1820.

[CreepySkeleton]

I think that might make the help message a bit more confusing.

You can hide the deprecated flag from the help message.

[CreepySkeleton]

You can define input_pos as required_unless(input_flag). This will give you exactly what you want.

[jan24]

Hi @casey
I meet the same issue like you, I am trying to develop a cmd tool like tee, it accepts any number of positional argument FILE, with -a means append, or without -a means overwrite. I have to define two FILE arguments, it's not very good, I am new to Clap, is there any way to dealwith it today? thankyou

ping www.google.com | tee
ping www.google.com | tee 1.log -a 2.log 3.log -a 4.log #

[tmillr]

I have the same issue and similar requirements. I'm using the derive interface. What I want is rather common, I just want to be able to accept multiple filenames via -f, --file, or positional. I first tried using visible_short_alias = 'f' on the positional argument, but that didn't work (i.e. passing -f somefilename becomes a runtime error)? This is kinda confusing. If that's not allowed, perhaps it should be a compile-time error detected by clap?

I guess I could use two different arg declarations, but I need the file names to go into the same Vec. So maybe I need to use an arg group? Lastly, I'd like to assert requirements: at least one filename must be passed but it does not matter how it is passed. What is the best way to accomplish this? I ask because ArgGroup doesn't have a method to define how many usages/values are allowed (e.g. like num_args() from Arg). Thanks

[epage]

(i.e. passing -f somefilename becomes a runtime error)? This is kinda confusing. If that's not allowed, perhaps it should be a compile-time error detected by clap?

So long as the error is reported as an assert during Command::debug_assert, that is expected behavior. There are a lot of conditions we can't check at compile time and rely on these asserts.

I guess I could use two different arg declarations, but I need the file names to go into the same Vec.

Why is that a hard requirement?

Id like to assert requirements: at least one filename must be passed but it does not matter how it is passed. What is the best way to accomplish this?

You define that on each arg (positional and named) and then make the group required.

[tmillr]

hmmm for me it isn't reported as an error when doing Command::debug_assert either (cargo test unoptimized debug build). It seems to allow declaring a short flag alias on a positional arg (via the derive interface) even though this errors at runtime when you try to pass the flag.

I just recently started using clap and I got a little hung up on this. I was just wondering what would be the best, simplest, or most idiomatic way to accomplish what I am trying to accomplish. That is all.

You define that on each arg (positional and named) and then make the group required.

Thank you for the input. I guess I just need an arg group and then maybe some manual verification (for example if I want to require 0 < n <= MAX file names, disregarding their source). And then I suppose that all of the filenames could be retrieved at once via one of the methods on ArgMatches?

This isn't that hard to do, but it's not as simple/nice as just using a single attribute (e.g. like when declaring an alias for a flag/non-positional).

[epage]

hmmm for me it isn't reported as an error when doing Command::debug_assert either (cargo test unoptimized debug build). It seems to allow declaring a short flag alias on a positional arg (via the derive interface) even though this errors at runtime when you try to pass the flag.

Feel free to create an issue

I guess I just need an arg group and then maybe some manual verification (for example if I want to require 0 < n <= MAX file names, disregarding their source). And then I suppose that all of the filenames could be retrieved at once via one of the methods on ArgMatches?

Yes, if you want to support mixing arguments, it requires more manual work

This isn't that hard to do, but it's not as simple/nice as just using a single attribute (e.g. like when declaring an alias for a flag/non-positional).

imo this is a bit off the beaten path so pushing the cost onto your application makes sense compared to supporting this native in clap, increasing binary size / build times and making the API harder to browse (the more we have, the easier it is to miss what functionality we have)