Program to upgrade configuration files

Question

When upgrading Ubuntu (and probably other *nixes), the upgrade process will show a diff of changed configuration files and ask whether I'd like to replace them, keep the old version, or manually merge them. I couldn't find any such programs with Google or searching through the Ubuntu packaging documentation. Do you know of any such programs which have the following features?

• Few or no dependencies (ideally a single shell script).
• Shell only (ideally without curses).
• Does not try to be "clever," for example by automatically merging.

Edit: I've written this small thing to do some preliminary checks and ask the user what to do, but it's not very flexible or nice:

for path
do
    if [ ! -e "${path}.new" ]
    then
        # No new revision; skip
        continue
    fi

    if [[ $(diff "${path}"{,.new} | grep '^[<>]' | grep -v '^[<>][[:space:]]*\(#\|START=\)' | wc -l) -eq 0 ]]
    then
        # No interesting lines; skip
        continue
    fi

    clear
    diff -u "${path}"{,.new}

    unset action
    while [[ ! "${action-}" =~ ^[sr]$ ]]
    do
        echo "Do you want to replace $path with ${path}.new?"
        read -s -n 1 -p $'[s]kip, [r]eplace: \n' action
    done

    case "$action" in
        s)
            continue
            ;;
        r)
            cp -v "${path}"{,.new}
            ;;
        *)
            echo "Invalid action ${action}!"
            exit 2
    esac
done

Answer 1

I strongly suspect the program you've seen is dpkg the low-level of package management in Debian-ish distributions (using apt(itude)). see here for a blog post explaining its configuration file management.

You could probably hijack this function, i.e., create your own .deb packages - which, I suspect, might be pretty much hassle for what you're trying to achieve.

There's another way to go, you could have a look at NetBSD's etcupdate tool (while it's rather NetBSD-specific, you might find its source (shell script) interesting nonetheless). Apparently, Gentoo has an etc-update, too, but I could find neither sources nor more information (the link also mentions dispatch-conf, could be interesting, too; I don't know.)