Since I didn't see anyone mention this (now watch someone submits a node that does while I'm busy typing), if you don't really need a regular expression, you might be better off just using index

#!/usr/bin/perl

$_ = 'TATATATATATA';
$str = "TATA";
$p = -1;
while (1) {
    $p = index($_,$str,$p+1);
    last if $p < 0;
    print "Found $str at position $p\n";
}
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