#!/usr/bin/perl -l
use warnings;
use strict;

# get the header into an array
my @header = split /\s+/, <DATA>;

# conjure a regex using the name of columns you wanted
# which is the array you have
my $to_find = join( '|' => qw(nat pls kac) );
my $reg_to_use = qr/$to_find/;

# get the index of the header you need
my @index = grep { $header[$_] =~ /$reg_to_use/ } 0 .. $#header;

print join( "\t" => @header[@index] );

while (<DATA>) {
    print join( "\t" => ( split /\s+/, $_ )[@index] );
}

__DATA__
nat     pls     fof     tri     pls     fof     tri	kac
0.1     0.1     0.23    0.1	0.1     0.23    0.1	0.31
2.3     1.8     3.2     4.4     1.8     3.2     4.4	3.21
5.5     3.2     8.6.    7.9     3.2     8.6.    7.9	2.89

##</code><code>##

nat	pls	pls	kac
0.1	0.1	0.1	0.31
2.3	1.8	1.8	3.21
5.5	3.2	3.2	2.89