Fore! 
perl -pi.bak -e 'BEGIN{$/=$u}s//\n/' foo*

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PS Clarification on my update above. I don't remember giving any hints on how to do this as a one-liner.

UPDATE
Obvious improvement. Dropped the $ off of the u.

UPDATE 2
Um, without it you can add a return to the end of the file as well. The $ is back.

In reply to Re (tilly) 2: Yet another one-liner by tilly
in thread Yet another one-liner by wardk

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