#!/usr/bin/perl -w

use Data::Dumper;

my @aoa;

push @aoa, [ "null", "44", "4" ];
push @aoa, [ "6", "24", "6" ];

my $array = \@aoa;

#  show my data structure
print Dumper $array;


my $test = "xray";


#  change first list element to variable "$test" if it isn't a number.
@array =  map { $_->[0] =~ s/[0-9]*/$test/ } @$array ;

print Dumper \@array;