perl -p -e 'BEGIN { undef $/ } s/\n{2,}/\n/g'

[download]

Which can be shortened to: 

perl -p0777e 's/\n{2,}/\n/g'

[download]
See perldoc perlrun for details of perl's -0 option.

In reply to Re^3: newlines in regular expressions by eyepopslikeamosquito
in thread newlines in regular expressions by gitarwmn

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