tr/// のいろいろな使い方メモ

$w = 'BOOK@RFS.JP';
$w =~ tr/A-Z/a-z/; # 小文字に正規化
print $w,"\n";
> book@rfs.jp 

$cnt = $w =~ tr/././; # $w に含まれる . の数を数える
print $cnt,"\n";
> 1

$w =~ tr/a-zA-Z/ /cs;  # 英字以外をスペースに変換
print $w,"\n";
> book rfs jp

$w =~ tr/a-zA-Z//s; # 連続した単語をひとつにまとめる
print $w,"\n";
> bok rfs jp 

http://www.rfs.jp/sb/perl/02/09.html