Temporarily imports key to sign without changing existing pubring

temp-sign.sh

#!/usr/bin/env bash
#
# Copyright (c) <year> <copyright holders>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy of
# this software and associated documentation files (the "Software"), to deal in
# the Software without restriction, including without limitation the rights to
# use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
# the Software, and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
# FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
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# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#

set -e

#
# This is probably NOT production-ready!
#

GNUPGHOME=${GNUPGHOME:-$HOME/.gnupg}

echo 'Backing up pubring' >&2
cp $GNUPGHOME/pubring.gpg $GNUPGHOME/pubring.gpg.bak

echo -n 'Key to sign? ' >&2
read signee
echo -n 'Sign with key? ' >&2
read signer

gpg --recv-keys $signee

echo 'Please verify fingerprint of key receiving signature: ' >&2
gpg --fingerprint $signee >&2
echo
echo -n 'Is this fingerprint correct? (y/N) ' >&2
read fpr_correct
echo

if [[ ! $fpr_correct =~ [yY] ]]; then
  echo 'Fingerprint is not correct! Abort!'
  exit 1
fi

gpg --default-key $signer --edit-key $signee sign >&2

gpg --armor --export $signee

echo 'Replacing pubring' >&2
rm $GNUPGHOME/pubring.gpg
mv $GNUPGHOME/pubring.gpg.bak $GNUPGHOME/pubring.gpg