#!/bin/sh
# make-backup-file-name -- print the next numbered emacs-style backup file
#                          name for a given file on disk
# Author: Noah Friedman <friedman@splode.com>
# Created: 1994-01-14
# Public domain

# $Id: make-backup-file-name,v 1.3 2018/10/12 05:59:44 friedman Exp $

# Commentary:

# Usage: make-backup-file-name [filename]
#
# Return the next emacs-style backup file name for a given file on disk,
# based on the VERSION_CONTROL environment variable.
# `t' or `numbered' means make numeric backup versions unconditionally.
# `nil' or `existing' means make them for files that have some already.
# `never' or `simple' means do not make them.

# Code:

name=$1

case $VERSION_CONTROL in
    never | simple )
        result=$name~ ;;

    * )
        highest=`for f in "$1".~*~ ; do echo "$f"; done |
                 sed -ne '/.*\.~\([0-9][0-9]*\)~$/{s//\1/p;}' |
                 sort -rn |
                 sed -e 1q`
        case $highest in
            '' ) highest=0 ;;
        esac

        case $VERSION_CONTROL in
            nil | existing )
                case $highest in
                    0 ) result=$name~ ;;
                esac ;;

            t | numbered | * )
                next=`expr $highest + 1`
                result=$name.~$next~ ;;
        esac ;;
esac

echo "$result"

# make-backup-file-name ends here