Does it have to be a regex? You can use split, if you don't mind the whitespace being mangled up. I guess you don't really care. 
my @words = split / /, $string, 6;
$words[-1] = '...' if @words==6;
$string = join ' ', @words;

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Hmm... that does add a space before the final ellipsis. A beauty spot, or a fatal flaw?

In reply to Re: get first e.g. 5 words and replace the remaining string with ... with one regex by bart
in thread get first e.g. 5 words and replace the remaining string with ... with one regex by dreamy

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