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t6d
Asked: 2010-10-06 06:56:06 +0800 CST

How to extract hostname from $(who am i)

  • 772

I try to extract the hostname from the following string (created using who am i):

username pts/0        2010-10-05 17:30 (www.example.com)

I need a solution which also works if (www.example.com) is not present which is the case when I am logged in locally. Furthermore the solution also has to work on a Mac where who am i returns the following string:

username ttys006      Oct  5 16:47 (www.example.com)

The problem is that the mac puts spaces in the date which makes it hard to use cut. I think, there must be a solution using sed to extract the substring, but I have problems figuring out how to use sed appropriately.

Update: Mad's approach

This approach only works well if there are actually parentheses present. If not, the following happens:

$ who am i | cut -f2 -d '(' | tr -d ')'
username ttys006      Oct  5 16:47
linux bash sed strings

4 Answers

  1. Best Answer

    This is where awk is the best tool. awk -F"[()]" '{print $2}' should pull out what's in parenthesis. Prints nothing if it's not there. So...

    $ who am i | awk -F"[()]" '{print $2}'
    www.example.com


    --Christopher Karel

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  2. You can use who am i | grep -o -e "\((.*)\)" on both systems, and it simply returns an empty string if you're logged in locally.

    • 5

  3. If you like cut (and I'm not saying there aren't more elegant ways to do it, but you chose the tool, and I rather like cut, too), try

    who am i | cut -f2 -d\( | tr -d ')'

    You take the second field, using left-paren as the separator (whcih will include the closing paren, though not the opening one), and then use tr to delete the close-paren.

    I'm not sure about the case when the string isn't present, as all the times I try it on a locally logged-on machine I get something returned in the brackets. Could you give an example of what you get under those circumstances?

    • 2

  4. Here's a sed version which works with or without parentheses around the hostname or spaces in the date:

    who am i | sed 's/.* (\?\([^)]*\))\?$/\1/'
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