Hello battingboy, and welcome to the Monastery!

If we assume that:

• your x values are contained in the file “x.dat”, which resides in the same directory as the Perl script
• the values you want are in the 4^th column (which is number 3, because we’re counting columns as offsets from the left, so the first column is number 0)
• all data values are separated by whitespace
• you want all the values in the column

then you can extract the x values like this:

#! 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;
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And of course you will need to repeat this for the y values (which you specify are in a different file).

Hope that helps,