Linux ip-172-26-7-228 5.4.0-1103-aws #111~18.04.1-Ubuntu SMP Tue May 23 20:04:10 UTC 2023 x86_64
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#!/bin/sh -e
if test $# -eq 0
then
echo "usage: $0 shellname [shellname ...]" 1>&2
exit 1
fi
file=/etc/shells
# I want this to be GUARANTEED to be on the same filesystem as $file
tmpfile="${file}.tmp"
otmpfile="${file}.tmp2"
set -o noclobber
cleanup() {
rm -f "$tmpfile" "$otmpfile"
}
trap cleanup EXIT
if ! cat "$file" > "$tmpfile"
then
cat 1>&2 <<EOF
Either another instance of $0 is running, or it was previously interrupted.
Please examine ${tmpfile} to see if it should be moved onto ${file}.
EOF
exit 1
fi
# this is supposed to be reliable, not pretty
for i
do
REALDIR="$(dirname "$(realpath -m "$i")")/$(basename "$i")"
for j in "$i" "$REALDIR"
do
grep -v "^${j}$" "$tmpfile" > "$otmpfile" || true
mv "$otmpfile" "$tmpfile"
done
done
chmod --reference="${file}" "${tmpfile}" || chmod $(stat -c %a "${file}") "${tmpfile}"
chown --reference="${file}" "${tmpfile}" || chown $(stat -c %U "${file}") "${tmpfile}"
mv -Z "${tmpfile}" "${file}" || mv "${tmpfile}" "${file}"
trap "" EXIT
exit 0
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