unix command to remove empty lines in a file

Question

How do I remove empty/blank (including spaces only) lines in a file in Unix/Linux using the command line ?

contents of file.txt

Line:Text
1:<blank>
2:AAA
3:<blank>
4:BBB
5:<blank>
6:<space><space><space>CCC
7:<space><space>
8:DDD

output desired

1:AAA
2:BBB
3:<space><space><space>CCC
4:DDD

Thanks Michael

Answer 1

This sed line should do the trick:

sed -i '/^$/d' file.txt

The -i means it will edit the file in-place.

Answer 2

sed '/^$/d' file.txt

d is the sed command to delete a line. ^$ is a regular expression matching only a blank line, a line start followed by a line end.

Answer 3

You can use the -v option with grep to remove the matching empty lines.

Like this

grep -Ev "^$" file.txt