How to remove empty/blank lines from a file in Unix (including spaces)?

This sed line should do the trick:

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

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

grep

Simple solution is by using grep (GNU or BSD) command as below.

• Remove blank lines (not including lines with spaces).

  grep . file.txt
  

• Remove completely blank lines (including lines with spaces).

  grep "\S" file.txt
  

Note: If you get unwanted colors, that means your grep is aliases to grep --color=auto (check by type grep). In that case, you can add --color=none parameter, or just run the command as \grep (which ignores the alias).

ripgrep

Similar with ripgrep (suitable for much larger files).

Remove blank lines not including lines with spaces:

rg -N . file.txt

or including lines with spaces:

rg -N "\S" file.txt

See also:

• How to remove blank lines from a file (including tab and spaces)?
• With sed: Delete empty lines using sed
• With awk: Remove blank lines using awk

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.

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

Like this

grep -Ev "^$" file.txt

Here is an awk solution:

awk NF file.txt

With Awk, NF only set on non-blank lines. When this condition match, Awk default action is to print the whole line.

To remove empty lines, you could squeeze new line repeats with tr:

cat file.txt | tr -s '\n' '\n'

Ex/Vim

Here is the method using ex editor (part of Vim):

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

For multiple files (edit in-place):

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

^{Note: The :bufdo command is not POSIX.}

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

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

xargs if you dont mind stripping leading whitespace

$ docker run -it --rm alpine sh
/ # cat <<eof > /tmp/file
> one
>
>   two
> three
>
>
>   four
> eof
/ # cat /tmp/file
one

  two
three


  four
/ # cat /tmp/file | xargs -n1
one
two
three
four

For me @martigin-heemels command was throwing error this fixed it (ie a dummy param to i),

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