Use substr. Also, testing if $val5 is defined and also not an empty string is redundant; I've changed it below.

my $page_link;
if ($val[5]) {
    # construct link if value is not NULL (undef) or empty
    my $linktext = $val[5];
    $linktext = substr($linktext, 0, 35) . "..." . substr($linktext, -
+15)
        if length($linktext) > 53;

    $page_link = a ({-href => $val[5]}, $linktext);
}

### other variables here ### then

print " - $page_link" if defined ($page_link);
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Update Fixed typo.

Update2 Added note about if condition.

Update3 Just noticed that in the root node the 5's are linked. Since they aren't in code blocks, I assumed that you typed $val[5] and they were turned into links without you realizing. Next time use the <code> tags. (OT, looking at all the updates I've done, I should probably stop popping those penguin mints... ;-)