How to delete empty lines using sed command under Linux / UNIX

I need to delete all empty lines but could not figure out sed command for the same. How do I delete all empty lines with sed under Linux or Unix-like systems?

sed is a stream editor and perfect for this kind of work. You need to use d command under sed which act as the delete function.

Sed Delete Empty Line Syntax

The syntax is as follows to delete empty lines using sed:
sed '/^$/d' <input-file>
echo "LINE" | sed '/^$/d'
echo "$VAR" | sed '/^$/d'
sed '/^[[:space:]]*$/d' input_file

Examples

So to delete all empty lines from a file called /tmp/data.txt, enter:
$ sed '/^$/d' /tmp/data.txt
To store output to another file use redirection operator:
$ sed '/^$/d' /tmp/data.txt > /tmp/output.txt
OR update the file using -i option:
$ sed -i '/^$/d' /tmp/data.txt

Removing all whitespace only using sed

Consider the following file:
more /tmp/data.txt
Sample outputs:

This is a test

foo

bar



nixCraft


Linux and Unix

To delete all empty lines, run:
sed '/^[[:space:]]*$/d' input.file
sed -i '/^[[:space:]]*$/d' input.file
sed -r '/^\s*$/d' input.file > output.file
sed -i '/^[[:space:]]*$/d' /tmp/data.txt
Verify with the help of cat command:
cat output.file
cat /tmp/data.txt

Deleting a line that matches a pattern

You can also match a word or a pattern to delete. For example
$ cat data.txt
Output:

This is a test
Linux rulez
Windows sucks
Redhat is good server disro

To delete all lines that contain a ‘Windows’ word, enter:
$ sed '/Windows/d' /tmp/data.txt > /tmp/output.data.txt
GNU Sed support -i option to edit files in place:
$ sed -i '/Windows/d' /tmp/data.txt

A note about awk

The awk command offers a much simpler solution as compared to sed command. In this example, remove all empty lines using awk:
awk 'NF' my_input > my_output
cat my_output

Conclusion

In short, use any one of the following sed syntax to remove all empty lines from a text file under Linux, macOS, *BSD and Unix-like systems:
sed '/^[[:space:]]*$/d' input > output
sed '/^\s*$/d' in > out
sed '/^$/d' input > output
sed -n '/^\s*$/!p' in.txt > out.txt
See more sed examples from our page:

• Delete text or paragraph between two sections using sed
• GNU sed man page here

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