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

countdiff() { ### @-
    ### count the number of lines changed between two files.
    ###
    ### **TODO:** don't use git for this. also, use patience algorithm.
    ###
    ### ```
    ### $ countdiff README-old.md README.md
    ### 739
    ### ```

    [ $# -gt 1 ] || { printf "%s\n" "$0: too few arguments" >&2; return 1; }
    [ $# -le 2 ] || { printf "%s\n" "$0: too many arguments" >&2; return 1; }
    git --no-pager diff --stat --no-color --no-index "$1" "$2" \
    | awk ' /changed/{print $4+$6;a=1}END{if(!a)print 0}'
}

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