I claim @astevan on Codeberg and @antoineeestevaaan on GitHub are the same person.

The commands

# use a temporary keyring
export GNUPGHOME="$(mktemp -d)"

# create a keypair and dump the public key
name="Temp"
gpg --batch --yes --quick-generate-key "$name" rsa2048 sign 1d
gpg --armor --export "$name" > pubkey.asc

# sign both documents
gpg --armor --detach-sign --output "lorem.txt.sig.asc" "lorem.txt"
gpg --armor --detach-sign --output "ipsum.txt.sig.asc" "ipsum.txt"

# delete temporary keyring
rm -rvf "$GNUPGHOME"

Note

the same script in Nushell

do {
    # use a temporary keyring
    $env.GNUPGHOME = mktemp -d

    # create a keypair and dump the public key
    let name = "Temp"
    gpg --batch --yes --quick-generate-key $name rsa2048 sign 1d
    gpg --armor --export $name | save pubkey.asc

    # sign both documents
    gpg --armor --detach-sign --output "lorem.txt.sig.asc" "lorem.txt"
    gpg --armor --detach-sign --output "ipsum.txt.sig.asc" "ipsum.txt"

    # delete temporary keyring
    rm -rvf $env.GNUPGHOME
}

Verification

( GNUPGHOME="$(mktemp -d)"; \
gpg --import pubkey.asc && \
gpg --verify "$file.sig.asc" "$file"; \
rc=$?; rm -rfv "$GNUPGHOME"; exit $rc )

Note

the “same” script in Nushell

do {
    # HELPERS
    def "color"       [c: string]: [ string -> string ] { $"(ansi $c)($in)(ansi reset)" }
    def "log info"    [log: string] { print $"[("INFO" | color cyan)] ($log)" }
    def "log warning" [log: string] { print $"[("WARNING" | color yellow_bold)] ($log)" }

    def download [file: string, --url: string] {
        log info $"downloading ($file | color purple) from ($url | color yellow)"
        curl -sfLo ($nu.temp-path | path join $file) $"($url)/($file)"
    }

    def verify [file: path, --sig: path] {
        let sig = $sig | default (
            $file | path parse | update extension { $"($in).sig.asc" } | path join
        )
        log info $"verifying ($file | color purple) with ($sig | color purple)"
        let ret = gpg --quiet --verify $sig $file | complete
        print $"(ansi default_dimmed)($ret.stderr | str trim)(ansi reset)"
        if $ret.exit_code == 0 {
            log info ("VALID SIGNATURE" | color green)
        } else {
            log warning ("INVALID SIGNATURE" | color red_bold)
        }
    }
    # HELPERS

    const GH = "https://raw.githubusercontent.com/antoineeestevaaan/antoineeestevaaan/refs/heads/main"
    const CB = "https://astevan.codeberg.page"

    $env.GNUPGHOME = mktemp -d

    download --url $CB "pubkey.asc"

    log info $"importing ("/tmp/pubkey.asc" | color purple) into temporary keyring ($env.GNUPGHOME | color purple)"
    gpg --quiet --import /tmp/pubkey.asc

    download --url $GH "ipsum.txt"
    download --url $GH "ipsum.txt.sig.asc"
    verify /tmp/ipsum.txt --sig /tmp/ipsum.txt.sig.asc

    download --url $CB "lorem.txt"
    download --url $CB "lorem.txt.sig.asc"
    verify /tmp/lorem.txt --sig /tmp/lorem.txt.sig.asc

    log info $"cleaning temporary keyring ($env.GNUPGHOME | color purple)"
    rm -rfv $env.GNUPGHOME
}