Try:

s/\n{2,}/EEEEE/g

[download]

Output on your dataset:

dogs rats
catsEEEEEfish

[download]

The \n{2,} notation matches 2+ newlines.

Edit: My apologies. Didn't notice the the OP's mentioning the possibility of other whitespace between the newlines.

In reply to Re: regular expression: match multiple newlines by Kenosis
in thread regular expression: match multiple newlines by wegelin

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