I'd always try to avoid a loop which could continue to fail like this. What if the file is deleted? You'll be looping forever.

use strict;
use LWP::Simple;

my $data = "";
my $try_count = 0;

while ($try_count++ < 5) {
    $data = LWP::Simple::get('http://somedomain/');
    last if defined $data;
    print "were is this file?\n";
    sleep(5);
};
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I also changed the criteria for success to check for 'definedness', because the LWP::Simple::get() function will explictly return undef if it fails.