ssh-setcomment

#!/bin/sh
set -e
set -u

fn_usage() { (
    echo ""
    echo "USAGE"
    echo "        ssh-setpass [ssh-key-file]"
    echo ""
    echo "EXAMPLE"
    echo "        ssh-setpass ~/.ssh/id_ed25519"
    echo "     OR"
    echo "        ssh-keygen -c ~/.ssh/id_ed25519"
    echo ""
); }

fn_grep_keyfiles() { (
    grep -r -- '-----BEGIN' ~/.ssh 2> /dev/null |
        cut -d: -f1 |
        sort -u ||
        true |
        while read -r my_keyfile; do
            echo "        ${my_keyfile}"
        done
); }

main() {
    my_key="${1:-"${HOME}/.ssh/id_rsa"}"

    if test "{my_key}" = "help" ||
        test "{my_key}" = "--help"; then
        fn_usage

        return 0
    fi

    if ! test -e "${my_key}"; then
        {
            echo ""
            echo "ERROR"
            echo "        '${my_key}' not found"
            echo ""
            echo "KEYS FOUND"
            if ! fn_grep_keyfiles; then
                echo "        (none)"
            fi
        } >&2

        return 1
    fi

    echo ""
    echo "${my_key}":
    ssh-keygen -c -f "${my_key}"
}

main "${1-}"