#!/usr/bin/env sh
# compat: +ash +bash +dash +zsh

bak() { ### @-
    ### backup files by creating copies and appending ".bak" to their names.
    ### this calls itself recursively to avoid clobbering existing backups.
    ###
    ### ```
    ### $ touch -d '2001-12-25 16:30:00' butts
    ### $ bak butts
    ### $ touch butts
    ### $ bak butts
    ### $ ls -l
    ### total 0
    ### -rw-r--r-- 1 notwa None 0 Aug  1 08:02 butts
    ### -rw-r--r-- 1 notwa None 0 Aug  1 08:02 butts.bak
    ### -rw-r--r-- 1 notwa None 0 Dec 25  2001 butts.bak.bak
    ### ```
    [ $# -gt 0 ] || { printf "%s\n" "$0: too few arguments" >&2; return 1; }
    local ret=0 f=
    for f; do
        if [ -e "$f.bak" ]; then
            bak "$f.bak" || { ret=1; continue; }
        fi
        cp -p "$f" "$f.bak" || ret=1
    done
    return $ret
}

[ -n "${preload+-}" ] || bak "$@"