How do I add newlines between lines printed on the command line?

Question

Mail logs are incredibly difficult to read. How could I output a blank line between each line printed on the command line? For example, say I'm grep-ing the log. That way, multiple wrapped lines aren't being confused.

Answer 1

sed G 
# option: g G    Copy/append hold space to pattern space.

G is not often used, but is nice for this purpose. sed maintains two buffer spaces: the “pattern space” and the “hold space”. The lines processed by sed usually flow through the pattern space as various commands operate on its contents (s///, p, etc.); the hold space starts out empty and is only used by some commands.

The G command appends a newline and the contents of the hold space to the pattern space. The above sed program never puts anything in the hold space, so G effectively appends just a newline to every line that is processed.

Answer 2

Use awk to add an extra newline. This also lets you filter out things you don't want.

awk '{print $0,"\n"}' | less

Answer 3

Use sed and replace the whole line by itself plus one extra newline character:

grep foo /var/log/maillog | sed -e "s/^.*$/&1\n/"

Answer 4

Pipe | any output to:

sed G

Example:

ls | sed G

If you man sed you will see

G Append's a newline character followed by the contents of the hold space to the pattern space.

Answer 5

Is this what you are after?

grep SPAM mail.log | while read -r line; do echo; echo $line; done

Answer 6

If it's for more than just have look, I prefer to send them to a text file and open with a text editor so you can set the lines to wrap or not and do searches easily... and delete the unwanted lines and so on without having to type a lot of commands.

cat file.log > log.txt and gedit log.txt or a terminal editor like nano

Edit: or cp file.log log.txt wich is of course easier and faster... thanks to KeithB comment