Provided your input-file is small enough to be read into memory, you can do this with a one-liner: 
perl -i.old -0777 -pe 's/\n+/\n/sg' input.txt

[download]
the original version of the file is kept as input.txt.old.

In reply to Re: replace multiple newline characters by morgon
in thread replace multiple newline characters by g_speran

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