>>560
こんな感じかな？

$filename = "hoge.txt";

open(FH, "+<$filename") or die;
read(FH, $buf, (stat(FH))[7]);
$buf =~ s/<(\d+)>/'<'.($1 + 20).'>'/esg;
seek(FH, 0, 0);
print FH $buf;
close(FH);