use strict;
my $input='
This is sample <This is sample text>
This is sample &lt;This is  sample text <a>this is sample text</a> sample text >
';

my @arr=$input=~m#&lt;[^<>]+(?:<a>.+?</a>[^<>]*)?>#g;
local $"="\n";
print "\n@arr";

##</code><code>##

&lt;This is sample text>
&lt;This is  sample text <a>this is sample text</a> sample text >