bash function to resolve a crate version in a terrible way

resolve_version.sh

# helper fn that returns version number given $crate or $crate/$semver.
# both must be url-encoded but the / must be a / if provided.
# doesn't handle cases where the version/crate/whatever doesn't exist.
resolve_version() {
    # Perform `HEAD` request to `docs.rs/$1` and dump the redirected URL.
    # We expect this to go to `docs.rs/crate/$crate/$version`
    # or `docs.rs/$crate/$version/$crate/` depending on if the crate has
    # docs or idrk. Maybe a couple other urls are possible, it
    # took a bit of testing for the `sed` script to handle all cases I found.
    #
    # Examples:
    #
    # `resolve_version bindgen` => 0.54.1
    # `resolve_version "bindgen/0.54"` => 0.54.1
    #
    # Note that the thing after the slash can be any semver version
    # requirement (you must % encode it first though): e.g. '>0.49.1,<=0.52':
    # `resolve_version "bindgen/%3e0.49.1%2c%3c%3d0.52"` => 0.52.0
    # see https://docs.rs/semver/0.10.0/semver/#requirements for details.
    #
    # The one caveat is that if you provide an exact version, e.g. `0.50.1`,
    # usually it is treated as `^0.50.1`, but docs.rs treats it as `=0.50.1`.
    #
    # So to get the newest compatible version of something, you must
    # have an explicit ^ (or, rather, %5e). That is:
    #
    # `resolve_version bindgen/0.54.0` => 0.54.0
    # `resolve_version bindgen/%5e0.54.0` =>  0.54.1
    #
    # I made a joke about this to the owner of docs.rs, and he indicated
    # that this is a cheap operation for them and that he doesn't really
    # mind if people use it to resolve versions. That said, see below
    # for some thoughts on how we can avoid abusing this good will.
    curl -Isw '%{redirect_url}' -o /dev/null "https://docs.rs/$1" \
        | sed -E 's=^https://docs.rs/(crate/)?[^/]+/==g ; s=/.+==g'
}