Reading output with lots of empty lines can be a waste of screen space. For instance, some System V versions of show all the blank lines between manual pages. To stop that, read your file or pipe it through cat -s. (Many versions of have a similar -s option.) The -s option replaces multiple blank lines with a single blank line. (If your cat doesn't have -s, see the sed alternative at the end.)
cat -s might not always seem to work. The problem is usually that the "empty" lines have SPACE, TAB, or CTRL-m characters on them. The fix is to let sed "erase" lines with those invisible characters on them:
| cat -s
Inand many , the CTRL-v character quotes the CTRL-m (RETURN) so that character doesn't end the current line.
If you don't have cat -s, then sed can do both jobs:
sed -e 's/^[[SPACE][TAB][CTRL-v][CTRL-m]]*$//' -e '/./,/^$/!d'