Question

I need to delete empty lines from a file (with spaces only – not null records).

The following command works only for null rows, but not in case of
spaces:

sed '/^$/d' filename

Can it be done using grep?

Answer 1

Use \s* for blank lines containing only whitespace:

sed '/^\s*$/d' file 

To save the changes back to the file use the -i option:

sed -i '/^\s*$/d' file 

Edit:

The regex ^\s*$ matches a line that only contains whitespace, grep -v print lines that don’t match a given pattern so the following will print all none black lines:

grep -v '^\s*$' file