#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my @R = ([qw(x y z)], [qw(a b c)], [qw(e f g)], [qw(h i j)]);

print Dumper \@R;

for my $rc (@R) {
  if ($rc->[0] eq "a") {
    splice @$rc, 0, 0, '#';
    print "$rc->[0]\t","$rc->[1]\t","$rc->[2]\t","$rc->[3]\n"
  }
}

print Dumper \@R;