$ perl -MO=Deparse,-p  -e"open $fh[$_],'>','split.'.$_ for 0..9;"  -nle"print {$fh[substr $_,3,1]} $_" big.log
BEGIN { $/ = "\n"; $\ = "\n"; }
LINE: while (defined(($_ = <ARGV>))) {
    chomp($_);
    open($fh[$_], '>', ('split.' . $_)) foreach (0 .. 9);
    print({$fh[substr($_, 3, 1)];} $_);
}
-e syntax OK