I have this command:

ptr=`host $hostname`

Which results in this:

test.tester.test has address

This Works!

What I want now is to extract only the IP address (, pass it to the variable $myptr and run the following command:

if $myptr | sed -n '/\(\(1\?[0-9][0-9]\?\|2[0-4][0-9]\|25[0-5]\)\.\)\{3\}\(1\?[0-9][0-9]\?\|2[0-4][0-9]\|25[0-5]\)/p' ; then
   host $myptr
   echo "No PTR Record found"

But it does not work. Please help?


You don't need any extravagant text processing on the output of host, you can just use dig +short to get only the IP address (and do the required reverse lookup on the IP).

dig +short "$hostname"


ip="$(dig +short "$hostname")"
host "$ip"

Or directly:

host "$(dig +short "$hostname")"
  • Legend, Thank you... Chasing my own tail there... – user2720970 Sep 20 '16 at 5:58

To extract ip you can awk it for example:

ptr=`host $hostname | awk '/has address/ {print $NF}'`
  • /has address/ mach only line that has this string as host can return much more for you. Try google for example.
  • print $NF - NF is awk's variable returning number of fields, so $NF points to last field.

Then you could use grep and check it's return code (sed will return 0 regardles if it will find your regexp or not. So doing something like this would work:

echo $ptr | egrep "your pattern"
if [ $? -eq 0 ]; then
    echo "This Works"

But you could simply check if $ptr contains an output. If host command won't find anything $ptr will be empty, so:

if [ -n $ptr ]; then
    echo "Works"
    echo "Not found :("

Take a look at man test:

          the length of STRING is nonzero
          the length of STRING is zero

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