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.

Solution 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.

Solution 2

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

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

Solution 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/"

Solution 4

Is this what you are after?

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

Solution 5

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.

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Comments

[Chris Johnsen]

You will probably want to use read -r to avoid treating backslash characters as special.

[Evan]

The -e isn't necessary. piping whatever | sed G ought to do the trick.

[camh]

A slightly simpler sed substitution would be 's/$/\n/', although @Chris Johnsen's 'G' command is even simpler.

[Dean Hill]

Why cat and not cp?

[laurent]

sure cp would be easier and faster!... lol - I was reading the other answers dealing with grep and awk so I wrote it the cat way but I'm correcting that, thanks

[Chris Johnsen]

@frabjous: Right, might as well leave off the -e since there we only need a single command argument.

[Michael Finco]

Can I give you like, +2? Nails it!

[biolinh]

but, it is only show in stdout, but not save it