nsr - name service resolver

nsr is a stupendously simple commandline name service resolver that feels/behaves sufficiently close to host(1).

Contrary to host(1) however, it does not bring its own resolver path and instead uses the libc resolver. This means it uses nsswitch.conf(5) and hosts(5) the same way as tools such as ping(8) or ping6(8) - if your system is configured that way.

It is also easier to type than getent hosts foobar, but you had a shell alias for that anyway...

All in all, you never want to be confronted with a setup where you need nsr, but if you do it eases the pain.

Example

• A typical nsswitch.conf will prefer /etc/hosts over results from DNS:

~% grep ^hosts /etc/nsswitch.conf
hosts: files dns

• Entries in your /etc/hosts might look like this:

~% grep foobar$ /etc/hosts
203.0.113.254       foobar.localdomain.example  foobar
2001:db8:0:1::254   foobar.localdomain.example  foobar

• host(1) goes directly to DNS, bypassing the system's resolver:

~% host foobar
Host foobar not found: 3(NXDOMAIN)
Exit 1

• since nsr uses the system resolver, the output is like this:

~% nsr foobar
foobar is an alias for foobar.localdomain.example
foobar.localdomain.example has IPv6 address 2001:db8:0:1::254
foobar.localdomain.example has IPv4 address 203.0.113.254

• reverse lookup looks like this:

~% nsr 203.0.113.254
254.113.0.203.in-addr.arpa domain name pointer foobar.localdomain.example

~% nsr 2001:db8:0:1::254
4.5.2.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa \
domain name pointer foobar.localdomain.example

Installation

Just copy it somewhere in your $PATH. $HOME/bin might work for you. Also remember +x etc.

Dependencies

nsr is written in Perl and requires version 5.14.0, in which getaddrinfo() and getnameinfo() were added to Core. If you have an older version of Perl, get Socket::GetAddrInfo from CPAN and adapt the code.

Known Features

• nsr does not detect if you replace a series of IPv6 zero blocks with :: that is not the longest series. It will instead give you funny results
• nsr does not support all valid IPv6 address notations known to man