sudoedit_watch.sh

#!/bin/bash

file=$1
# Ignore the command this script was run with to prevent infiniute recursion
editor=$(which -a $EDITOR | grep -v $0 | head -n1)

if test -z "$CURRENT_UID"; then
    export CURRENT_UID=$UID
fi

sha1() {
    printf $(sudo sha1sum "$1" | awk '{print $1}')
}

update_if_changed() {
    new_hash=$(sha1 "$tmpfile")
    if test "$file_hash" != "$new_hash"
    then
        cat "$tmpfile" >"$file"
        file_hash=$new_hash
    fi
}

file_exists() {
    test -f $1
}

file_writable() {
    test -w "$1"
}

dir_writable() {
    tmpfile=$(dirname $1)/.is_writable
    touch "$tmpfile" 2>/dev/null && rm "$tmpfile"
}

cleanup() {
    sudo rm -f "$tmpfile"
    ! test -z $job && kill $job 2>/dev/null;
    exit
}

if test -z "$file"; then
    echo "Usage; $0 <filename>" && exit
fi

# If we have write access, no need to use sudo
if  test $EUID -ne 0 && \
    (file_writable "$file" || \
    ! file_exists "$file" && dir_writable "$file");
then
    exec $editor "$file"
fi

# Gain root
if test $EUID -ne 0
then
    exec sudo -E $0 "$@"
fi

trap "cleanup" SIGINT

dir=$(dirname $file)
filename=$(basename $file)
tmpfile=$(mktemp --tmpdir=$dir -t .${filename}.XXX)

touch "$tmpfile" # Make sure temp file exists
chown $CURRENT_UID "$tmpfile"
chmod 600 "$tmpfile"
file_hash=da39a3ee5e6b4b0d3255bfef95601890afd80709 #empty file

if test -f "$file"
then
    file_hash=$(sha1 "$file")
    cat "$file" >"$tmpfile"
fi

# Background listener to update the actual file while the editor is still running
(
while true
do
    test ! -f "$tmpfile" && exit
    inotifywait -e modify "$tmpfile" -qq 2>/dev/null \
    && update_if_changed
done
)&

job=$!
disown # No job control messages in this shell

# Time for real action. Run the editor as the user
sudo -E -u \#$CURRENT_UID $editor "$tmpfile"

cleanup