Display specific word in file. To be used as varible, grep for email in log

Question

I'm looking to display just the email address in the /var/log/secure file. The email goes into a variable, so just grepping for lines won't work.

I know how to string together sed commands, but is there a cleaner way?

I could even scrap the idea altogether, if there is a cleaner way to get ssh key comment emails. I'm looking to find out which email comment, on the clients ssh key, was used to login. So far I have been using something like this..

 ssh root@localhost  "sleep 1 ; tail -1 /var/log/secure | ..."

I hope there is a better way, or at least a clean way to display just the email.

Answer 1

Why doesn't grep work out for you? It has the -o parameter to get only the match. So something like grep -o " .+@.+ " /var/log/secure should work. Only work out the expression to just match the email address.

Answer 2

As @Matteo mentioned, I've never seen the public key informations in /var/log/secure but if you want to display only email address from a text file, you can use egrep (for extended regex) with -o option, something like this:

$ egrep -o '[^ ]+@[^ ]+' input

or you must escape the plus if you use grep:

$ grep -o '[^ ]\+@[^ ]\+' input

You can also do it with sed:

$ sed -nr 's/.* ([^ ]+@[^ ]+).*$/\1/p' input