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

Try ex-way:

ex -s +'v/\S/d' -cwq test.txt

For multiple files (edit in-place):

ex -s +'bufdo!v/\S/d' -cxa *.txt

Without modifying the file (just print on the standard output):

cat test.txt | ex -s +'v/\S/d' +%p +q! /dev/stdin