debdiffconf, copy from https://a3nm.net/git/mybin/file/debdiffconf.html

debdiffconf

#!/bin/bash

# Usage: debdiffconf.sh <filename>
# Produce on stdout, a diff of <filename> against the first installed Debian
# package found that provides it.
# Returns the exit code of diff if everything worked, 3 or 4 otherwise.

base_name=$(basename $0)

required=( apt-get apt-file diff dpkg-deb dpkg-query realpath)
for binary in "${required[@]}"
do
    [ -x "$(command -v "$binary")" ] ||
    {
        echo -e "Error: Necessary program \'$binary\' is not installed. Aborting now.\n" >&2
        exit 4
    }
done

if [ $# -eq 0 ]
then
    echo "No arguments supplied, please pass in a filename. Try something like:\n\n$base_name /etc/squid/squid.conf\n" >&2
    exit 4
else
    FILE=$(readlink -f "$1")
fi

while read -r PACKAGE
do
    # verify from first installed package
    if dpkg-query --showformat='${Status}\n' -W "$PACKAGE" > /dev/null
    then
        # create a unique tmpdir that is still recognizable in the system
        DIR=$(mktemp --tmpdir -d "$base_name-$PACKAGE.XXXXXXXXXX")
        if cd "$DIR"
        then
            # install cleanup trap
            trap "{ cd -; rm -rf "$DIR"; exit $?; }" EXIT INT TERM HUP PIPE
        else
            echo -e "Cannot chdir to \'$DIR\'. Aborting now." >&2
            exit 1
        fi
        echo "Trying $PACKAGE…" >&2
        apt-get download "$PACKAGE" >&2
        # downloaded archive is the only file present...
        ARCHIVE=$(ls)
        mkdir contents
        # extract entire archive
        dpkg-deb -x "$ARCHIVE" contents/ >&2
        [ -f "contents$FILE" ] && diff --unified --minimal "contents$FILE" "$FILE"
        exit 0
    fi
done < <(apt-file -l search "$FILE")
# if we are here, it means we have found no suitable package
echo "Could not find original package for $FILE" >&2
exit 3

Thanks, included in 0334afa .