use strict;
use warnings;

my ( @array, %seen );
while ( my $line = <DATA> ) {

	if ( $line =~ /(amazing\.\S+)/ and not $seen{ lc $1 }++ ) {
		push @array, $line;
		#print $line;
	}
}

print for @array;

__DATA__
Today is amazing.nice day 
Today is amazing.nice but still I haven't done anything 
Yesterday was just a normal day 
Tomorrow probably will be amazing.new day