Is there a standard command-line tool to do a hostname lookup?

Question

I am in the shell and I want to know the corresponding IP address(es) for a hostname.

I know I could get it through Perl, PHP, Python or a number of other scripting languages (probably even awk!), and this will be my workaround, but I am surprised that there seems to be no command-line tool to do this, no simple wrapper around getaddrinfo().

Am I wrong? Is there one? host, dig and getent do not count, I want something that uses the libc and acts according to /etc/nsswitch.conf, and something that is probably installed on any (linux) system by default.

Moved here from https://stackoverflow.com/questions/20211326/is-there-a-standard-command-line-tool-to-do-a-hostname-lookup

Answer: I was wrong, getent does not exclusively look in /etc/hosts, it actually does a proper lookup.

Answer 1

the traditional tool for doing host name lookups is nslookup from bind, but it is being replaced with dig. both tools are dns speciffic and don't use nsswitch. getent hosts uses nsswitch, but much less used.

Answer 2

getent is certainly the right tool for the job but it is unfortunately not available everywhere, one of the reason being it is not mandatory being undefined by POSIX.

On the other hand, while it isn't either specified by the standard, arp is very unlikely not to be available on any server that does name resolution. As arp follows nsswitch.conf settings, only uses libc, is available on any Linux/Unix system, and provides an output that seems to be consistent between implementations, parsing its output would do the job:

$ arp stackoverflow.com | sed -e 's/.*(//' -e 's/).*$//'
198.252.206.16

Here is a shell function that uses that method, avoiding an issue with Linux arp which switch to a different output format in some corner cases:

resolve()
{
  : ${1:?Usage: resolve name}
  (
    PATH=$PATH:/usr/sbin
    ao=$(arp $1)
    [ "$(echo "$ao"|grep HWaddress)" ] && ao=$(arp -a $1)
    echo "$ao" | sed -e 's/.*(//' -e 's/).*$//'
  )
}