How to curl case-insensitive

Question

If I use this link to install docker-compose, I get Not Found error:

[root@hostname ~]# curl -L "https://github.com/docker/compose/releases/download/2.9.0/docker-compose-$(uname -s)-$(uname -m)" -o here
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100     9  100     9    0     0     37      0 --:--:-- --:--:-- --:--:--    37
[root@hostname ~]# cat here
Not Found

That's because the actual file is docker-compose-linux-x86_64 with small l, while:

[root@hostname ~]# echo $(uname -s)-$(uname -m)
Linux-x86_64

It returns capital L.

I saw man curl but did not see any entry for checking case-insensitive link.

Answer 1

It's not curl that decides case-insensitivity at all – link "checking" is the server's decision.

(In other words, HTTP clients do not have the opportunity to see the list of all possible URLs and choose a matching one. The only thing an HTTP client can do is give the exact URL to the server and let the server decide how to respond. Some servers are case-insensitive, some are not.)

But if you already know that you need a lowercase 'linux', you can just transform the uname output before giving it to curl, e.g. by piping it through tr A-Z a-z to change all uppercase letters to lowercase:

docker-$(uname -s | tr A-Z a-z)

or by using Bash's ${var,,} expansion to return a lowercase version of $var:

os=$(uname -s); arch=$(uname -m)

docker-${os,,}-${arch}

Finally, since there's only a small set of accepted values, and because the accepted values aren't guaranteed to be "uname but lowercase" in general, you could indirectly assign each possible value (using if or case blocks), for example:

case $(uname -s) in
    Darwin)    docker_os='darwin';;
    Linux)     docker_os='linux';;
    Cygwin)    docker_os='windows';;
    Microsoft) docker_os='windows';;
    *)         echo "Docker is not supported on this OS!" >&2; exit 1;;
esac

^{(Note: The 'windows' examples are completely made up. )}

Answer 2

Case sensitivity for the part after the domain names is up to the server.

To fully emulate case-insensitivity of the server, curl would have to try up to all possible combinations (…LiNUx…, …linUX…) and there's an enormous number of them.

If you know the server uses all-lowercase strings then a reasonable thing to do is to convert the URL to lowercase before supplying to curl. Example for Bash:

url="https://github.com/docker/compose/releases/download/2.9.0/docker-compose-$(uname -s)-$(uname -m)"
url="${url,,}"
curl -L "$url" -o here

BUT the right URL is with v2.9.0 and the server in question is actually case-insensitive for the docker-compose-… component. The simplest fix for you is just to add the missing v:

curl -L "https://github.com/docker/compose/releases/download/v2.9.0/docker-compose-$(uname -s)-$(uname -m)" -o here
#                                           this was missing ^

Without this v no conversion can help.

Answer 3

As others already pointed out, case insensitivity is configured serverside, there is nothing you can do to change that from your machine.

You could however use some other tools to convert the string to lowercase:

╭─user@machine ~ ‹main› 
╰─$ echo $(uname -s)-$(uname -m) | tr '[:upper:]' '[:lower:]'                                                                                                                                             
linux-x86_64