my $ham = "spam\tspam\tspam\t\tyam\tclam";
my @jam = ($ham =~ (m/^[^\t]*\t[^\t]*(?:\t([^\t]*)){3}\t[^\t]*$/));
print join("\n", '**', @jam, '**', '');

##</code><code>##

**
yam
**

##</code><code>##

**
spam

yam
**