You seem to have mistyped "tabs\t" for "$tabs\t". In that case, you can use the more elegant operator .=:

for ($i = 0; $i < $numTabs; $i++) {
  $tabs .= "\t";
}
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But, like jwkrahn wrote: you might as well use x instead of the loop, so this becomes:

$tabs .= "\t" x $numTabs;
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