List host key information from ~/.ssh/known_hosts

list-ssh-rsa-key-lengths

#!/bin/sh
# @(#)$KimmoSuominen: .cfg/home/bin/share/list-ssh-rsa-key-lengths,v 1.3 2023/03/05 20:24:14 kim Exp $
#
# List host key information from ~/.ssh/known_hosts
#
# 20230225  Kimmo Suominen
#

#
# Copyright (c) 2023 Kimmo Suominen
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
#
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer
#    in the documentation and/or other materials provided with the
#    distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

set -eu
umask 077

PATH=/bin:/usr/bin
export PATH

PROG="${0##*/}"

die()
{
    echo "${PROG}: ${@}" 1>&2
    exit 1
}

msg()
{
    echo "${PROG}: ${@}" 1>&2
}

usage()
{
    cat <<EOF
Usage:	${PROG} [file ...]

List host key information from ~/.ssh/known_hosts or the given files.
EOF
}

# 34567890123456789012345678901234567890123456789012345678901234567890123456789

if [ ${#} -lt 1 ]
then
    set -- "${HOME}/.ssh/known_hosts"
fi

WRKDIR="$(mktemp -d "${TMPDIR-/tmp}/${PROG}.XXXXXXXXXX")"
trap "rm -rf ${WRKDIR}" 0 1 2 15

KEY="${WRKDIR}/key.pub"

sed '/^#/ d; /^[ 	]*$/ d;' "${@}" \
| while read line
do
    echo "${line}" > "${KEY}"
    ssh-keygen -lf "${KEY}"
done