#!/bin/sh -e
if test $# -eq 0
then
echo usage: $0 shellname [shellname ...]
exit 1
fi
file=/etc/shells
# I want this to be GUARANTEED to be on the same filesystem as $file
tmpfile=${file}.tmp
set -o noclobber
trap "rm -f $tmpfile" EXIT
if ! awk '{print}' $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 ${file}.
EOF
exit 1
fi
for i
do
REALDIR="$(dirname $(realpath -m $i))/$(basename $i)"
for j in "$i" "$REALDIR"
do
if ! grep -q "^${j}$" $tmpfile
then
echo $j >> $tmpfile
fi
done
done
chmod --reference=$file $tmpfile
chown --reference=$file $tmpfile
mv $tmpfile $file
trap "" EXIT
exit 0
Mini Shell