That's overly complicated. Move the \b to the end.

$line =~ /\bh(?:e(?:l(?:l(?:o)?)?)?)?\b/i;
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In 5.10, you can even disable needless backtracking

$line =~ /\bh(?:e(?:l(?:l(?:o)?+)?+)?+)?+\b/i;
[download]