use warnings;
use strict;
use Data::Dumper qw(Dumper);

my $clk_new;
my @clk_new;

my @clk =  ('ux_prim_clk', 'ux_side_clk', 'ux_xtal_frm_refclk');

my @clk_output = map [ split /_/, $_ ], @clk;

print Dumper \@clk_output;

for ( my $c= 0; $c<= $#clk_output; $c++) {
   for ( my $d = 0; $d <= $#{$clk_output[$c]}; $d++ ) {
        $clk_new = join '_', $clk_output[$c];
        print Dumper $clk_new;
        push @clk_new, $clk_new;
    }
}

print Dumper @clk_new;