use utf8;
use strict;

my $s1 = "long_japanese_text_ i_utf8";
my $s2 = "short_japanese_text_in_utf8";
print index($s1, $s2)."\n";
print "found\n" if $s1 =~ /$s2/;

##</code><code>##

use strict;
use utf8;

my $s1 = "short_japanese_text_in_utf8";
open F, "<:encoding(sjis)", "file.txt";
while (<F>) {
  print "found\n" if /$s1/;
  print index($_, $s1)."\n";
}