Also this:

>perl -wMstrict -le
"my %replace = (rabbit => 'pap', triangle => 'tri', andso => 'on');
 ;
 my $search = join '|', keys %replace;
    $search = qr{ $search }xmsi;
 ;
 while (<>) {
   last if m{\A \s* \z}xms;
   s{ \b ($search) \b }{ $replace{lc $1} }xmsge;
   print qq{'$_'};
   }
"
Andso rabbit Xrabbit rabbitX XrabbitX RaBbIt
'on pap Xrabbit rabbitX XrabbitX pap
'
Triangle Triangles
'tri Triangles
'
[download]

See also perlretut, perlreref, perlrequick.