my %CommonSampleNames

open my $IN1, "file2.txt" or die $!;
my $head = <$IN1> ;## again use it if it has a header

while(<$IN1>){
chomp $_;
my @line = split(',', $_);
if(exists $hash1{$line[0]} ){ ## $line[0] is the sample name column
$CommonSampleNames{$line[0]} = 1;
}
}
close($IN1);