Fetch ipaddress and hostname from host file.

Shell Programming and Scripting
1

hello guys,

I have a query ,I am looking for a unix command using awk and grep that help me fetching a particular ip address and hostname from the host file.........??????

2

Hello,

Could you please provide us the input and expected output please for same.

Thanks,
R. Singh

3

You can do it directly with
grep -i <ip address> /etc/hosts

Not sure why you need to use awk. Please provide more details if you have any specific requirement.

4

Not sure why you would need -i with an IP address, but you would need it for an alphabetic host name search.

Do you want to get them into variables?

If you are searching for a name, you will need to use the -E flag and give a variety of strings to match, such as:-

  • First on line (IP address); followed by a space
  • First on line (IP address); followed by a tab
  • Preceded by space; last on line
  • Preceded by tab; last on line
  • Preceded by space; followed by a space
  • Preceded by space; followed by a tab
  • Preceded by tab; followed by a space
  • Preceded by tab; followed by a tab

You also need to trim off any comments that might be picked up by mistake too. Consider searching for prod this /etc/hosts file:-

100.100.100.1        host1      prod          # This is real production
200.200.200.2        host2      pre-prod      # This is not live yet.
300.300.300.3        host3      ex-prd        # This was prod for a bit

Remember that one IP address can have multiple host names associated with it in /etc/hosts. Try:-

cut -f 1 -d "#" /etc/hosts |  grep -Ei \
"^search-string |^search-string<tab>| search-string$|<tab>search-string$| search-string | search-string<tab>|<tab>search-string |<tab>search-string<tab>" | \
  read my_ip my_host1 my_host2 my_host2 my_host3 my_other_hosts

use the tab character where it shows <tab> rather than use that as a literal string.

The ^ indicates start of line.
The $ indicates end of line.
The | is a logical or between each of the possible searches.

Even then, I might not have considered everything, but if you are looking for information on other servers, it's best to use a name and let the server figure it out through DNS in any case. If you need to talk to a particular application, get a CNAME set up in DNS and refer to that, so that if you move the application, you redirect the CNAME entry and your code need toy change.

I hope that this helps,
Robin
Liverpool/Blackburn
UK