my %hValuesInColumn2;

# use while, not foreach
while (my $line = <F2>) {

  #get rid of trailing new line
  chomp $line;

  # strip remaining leading and trailing whitespace
  # (if that is an issue)
  $line =~ s/^\s+//;  #leading
  $line =~ s/\s+$//;  #trailing

  # record field value
  $hValuesInColumn2->{$line} = 1;
}

# extracting the keys may not even be necessary
# see first part of this answer.
my @unique_f = keys %hValuesInColumn2;