Quick-&-dirty helper script to generate ssh key pair & related config section

ssh-keygen-helper.sh

#!/usr/bin/env bash

set -e
set -x

usage()
{
	echo "Usage: ${0} localhostname username serverhostname [ssh_alias remotehostname]"
	echo "Info:"
	echo -e "\tlocalhostname - for convinience purpose in key config"
	echo -e "\tusername - valid username at remote server"
	echo -e "\tserverhostname - for convinience purpose in key config"
	echo -e "\tssh_alias - for convinience purpose in ~/.ssh config"
	echo -e "\tremotehostname - valid pingable hostname of remote server for ~/.ssh config"
	echo ""
	echo "Sample:"
	echo -e "\t${0} myhomepc git github gh github.com"
	exit 1
	return 1
}

test ${#} -ge 3 || usage

test -n "${1}" || usage
test -n "${2}" || usage
test -n "${3}" || usage

host=${1}
user=${2}
target=${3}

ssh_dir="${HOME}/.ssh"
ssh_conf="${ssh_dir}/config"
ssh_keyfile_full="${ssh_dir}/${host}_${user}@${target}"
ssh_keyfile_home="~/.ssh/${host}_${user}@${target}"

cmd="ssh-keygen -t ed25519 -C ${host}:${user}@${target} -f ${ssh_keyfile_full}"
ssh-keygen -t ed25519 -C "${host}:${user}@${target}" -f "${ssh_keyfile_full}"

if [ -n "${4}" ] && [ -n "${5}" ]; then
test -f "${ssh_conf}" || touch "${ssh_conf}"
cat <<EOF >> "${ssh_conf}"

# generated at `date +"%Y.%m.%d %H:%M:%S"` using:
# \$ ${cmd}
Host ${4}
	HostName ${5}
	User ${user}
	IdentityFile ${ssh_keyfile_home}
	PubkeyAuthentication yes
	PasswordAuthentication no

EOF
fi;