Oh, I have to pass the argument with quotes, I see. But this one is not working for me

[ALEX5402]

Oh, I have to pass the argument with quotes, I see. But this one is not working for me

[faho]

No, you need to pass the outer argument with quotes.

This works:

function ytd
    youtube-dl -t $argv[1]
end

ytd "https://youtu.be/HPGvrxjT7aY?si=94x7gGDp76rTI4dX"

You need to quote the argument where the string is - the ? is special, so that needs to be quoted where it is, not later.

That will work but I was hoping to be able to pass the argument without quotes, to have the function add them. Is this possible?

It is not. The argument is expanded before the function ever runs.

You can fiddle something together with abbreviations, which is a lot easier with abbr --command ( #10452):

function quote_arg
    string escape -- $argv
end

function ytd
    youtube-dl $argv
end

abbr -a --command ytd --function 'quote_arg' --regex '.*' quotearg

(without that you'll have to mess with commandline to check if it's an argument to ytd)

But in general, quoting is a fact of life. You cannot ignore quoting, the entire language is based on expansion - if it sees an unquoted $, it'll try to expand a variable, if it sees an unquoted *, it'll glob, if it sees an unquoted ; it'll end the command.

For ? in particular, we're removing it, and it's removed-by-default in the next release, so urls usually won't have special characters in them anymore.