Remove empty lines in a text file via grep

Question

FILE:

hello

world

foo

bar

How can I remove all the empty new lines in this FILE?

Output of command:

Answer 1

Perl might be overkill, but it works just as well.

Removes all lines which are completely blank:

perl -ne 'print if /./' file

Removes all lines which are completely blank, or only contain whitespace:

perl -ne 'print if ! /^\s*$/' file

Variation which edits the original and makes a .bak file:

perl -i.bak -ne 'print if ! /^\s*$/' file