#!/usr/bin/perl
use warnings;
use strict;
use Encode;
use Encode::Guess;

open (DATA, "<:utf8", "a.txt") or die $!;
binmode DATA, ":utf8";
my $line = <DATA>;

while($line){
	my $decoder = guess_encoding($line);
	if (ref($decoder) eq 'Encode::utf8'){
	print "File is in UTF-8\n";
        #doing something
	}
$line = <DATA>;
}
__END__