#!/usr/bin/env sh
# YES_ZSH
# YES_BASH
# YES_DASH
# YES_ASH
# YES_BB_AWK

similar() { ### @-
    ### highlight adjacent lines up to the first inequivalent character.
    [ $# -eq 0 ] || { printf "%s\n" "$0: does not take arguments" >&2; return 1; }
    awk '
    {
        i=0
        for(c=1;c<length;c++)
            if(substr($0,c,1)==substr(L,c,1)) i++
            else break
        #print substr($0,1,i) "\033[7m" substr($0,i+1) "\033[0m"
        print "\033[31m" substr($0,1,i) "\033[0m" substr($0,i+1)
        L=$0
    }'
}

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