#! perl
use strict;
use warnings;
use Data::Dump;

my $file      = 'x.dat';
my $column    =  3;
my $separator =  qr{\s+};    # split on whitespace
my @values;

open(my $fh, '<', $file)
    or die "Cannot open file '$file' for reading: $!";

while (my $line = <$fh>)
{
    chomp $line;             # remove the trailing newline
    my    @cols = split $separator, $line;
    push  @values, $cols[$column];
}

close $fh
    or die "Cannot close file '$file': $!";

dd \@values;