You'll have better luck with regex if you think in terms of what you do want to match rather than what you don't want to match or what's around what you want to match. 

my ($match) = $body =~ /(?<=a)([^c]*c[^c]*c[^c]*)(?=c)/;

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The above can also be written as 
my ($match) = $body =~ /(?<=a)([^c]*(?:c[^c]*){2})(?=c)/;

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Or maybe you want 
my ($match) = $body =~ /(?<=a)([^ac]*(?:c[^ac]*){2})(?=c)/;

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In reply to Re: Regex text extraction b/w first intance of pattern X and third instance of pattern Y. by ikegami
in thread Regex text extraction b/w first intance of pattern X and third instance of pattern Y. by cdherold

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