mjhjmtu

With host from the dnsutils package:

$ host unix.stackexchange.com
unix.stackexchange.com has address 64.34.119.12

(Corrected package name according to the comments. As a note other distributions have host is different packages: Ubuntu bind9-host, openSUSE bind-utils, Frugalware bind.)

I have a tool on my machine that seems to do the job. The man page shows it seems to come with mysql... Here is how you could use it:

resolveip -s unix.stackexchange.com
64.34.119.12

The return value of this tool is different from 0 if the hostname cannot be resolved :

resolveip -s unix.stackexchange.coma
resolveip: Unable to find hostid for 'unix.stackexchange.coma': host not found
exit 2

UPDATE
On fedora, it comes with mysql-server :

yum provides "*/resolveip"
mysql-server-5.5.10-2.fc15.x86_64 : The MySQL server and related files
Dépôt  : fedora
Correspondance depuis :
Nom de fichier  : /usr/bin/resolveip

I guess it would create a strange dependency for your script...

The following command using dig allows you to read the result directly without any sed/awk/etc. magic:

$ dig +short unix.stackexchange.com
64.34.119.12

dig is also included in the dnsutils package.

Note: dig has a return value of 0, even if the name could not be resolved. Thus, you'd need to check if the output is empty instead of checking the return value:

hostname=unix.stackexchange.com

ip=`dig +short $hostname`

if [ -n "$ip" ]; then
 echo IP: $ip
else
 echo Could not resolve hostname.
fi

Note 2: If a hostname has multiple IP addresses (try debian.org, for example), all of them will be returned. This "problem" affects all of the tools mentioned in this question so far:

getent hosts unix.stackexchange.com | cut -d' ' -f1

The solutions given so far mostly work in the simpler case: the hostname directly resolves to a single IPv4 address. This might be the only case where you need to resolve hostnames, but if not, below is a discussion on some cases that you might need to handle.

Chris Down and Heinzi briefly discussed the case where the hostname resolves to more than one IP addresses. In this case (and others below), basic scripting under the assumption that a hostname directly resolves to a single IP address may break. Below, an example with a hostname resolving to more than a single IP address:

$ host www.l.google.com
www.l.google.com has address 209.85.148.147
www.l.google.com has address 209.85.148.103
www.l.google.com has address 209.85.148.99
www.l.google.com has address 209.85.148.106
www.l.google.com has address 209.85.148.105
www.l.google.com has address 209.85.148.104

But what is www.l.google.com? This is where the alias case needs to be introduced. Let's check the example below:

$ host www.google.com
www.google.com is an alias for www.l.google.com.
www.l.google.com has address 74.125.39.103
www.l.google.com has address 74.125.39.147
www.l.google.com has address 74.125.39.105
www.l.google.com has address 74.125.39.99
www.l.google.com has address 74.125.39.106
www.l.google.com has address 74.125.39.104

So www.google.com does not directly resolve to IP addresses, but to an alias that itself resolves to multiple IP addresses. For more information on aliases, check here. Of course, the case where an alias has a single IP address is possible, as shown below:

$ host g.www.ms.akadns.net
g.www.ms.akadns.net is an alias for lb1.www.ms.akadns.net.
lb1.www.ms.akadns.net has address 207.46.19.190

But can aliases be chained? The answer is yes:

$ host www.microsoft.com
www.microsoft.com is an alias for toggle.www.ms.akadns.net.
toggle.www.ms.akadns.net is an alias for g.www.ms.akadns.net.
g.www.ms.akadns.net is an alias for lb1.www.ms.akadns.net.
lb1.www.ms.akadns.net has address 207.46.19.254

$ host www.google.fr
www.google.fr is an alias for www.google.com.
www.google.com is an alias for www.l.google.com.
www.l.google.com has address 74.125.39.147
www.l.google.com has address 74.125.39.103
www.l.google.com has address 74.125.39.99
www.l.google.com has address 74.125.39.106
www.l.google.com has address 74.125.39.104
www.l.google.com has address 74.125.39.105

I did not find any example where a hostname resolves to an alias that does not resolve to an IP address, but I think the case might occur.

More than multiple IP addresses and aliases, is there some other special cases... what about IPv6? You could try:

$ host ipv6.google.com
ipv6.google.com is an alias for ipv6.l.google.com.
ipv6.l.google.com has IPv6 address 2a00:1450:8007::68

Where the hostname ipv6.google.com is an IPv6-only hostname. What about dual-stack hostnames:

$ host www.facebook.com
www.facebook.com has address 66.220.153.15
www.facebook.com has IPv6 address 2620:0:1c08:4000:face:b00c::

Again about IPv6, if your host is IPv4 only, you can still resolve IPv6 addresses (tested on a IPv4 only WinXP and with ipv6.google.com, you could try it on Linux). In this case, the resolution succeeds, but a ping fails with an unknown host error message. This might be a case where your scripting fails.

I hope those remarks were useful.

To avoid the problem with aliases and always get a single IP address ready for use:

python -c 'import socket; print socket.gethostbyname("www.example.com")'

ping -q -c 1 -t 1 your_host_here | grep PING | sed -e "s/).*//" | sed -e "s/.*(//"

works without dependencies on other systems (and for hosts specified in /etc/hosts)

Simple but usefull:

1. getent ahostsv4 www.google.de | grep STREAM | head -n 1 | cut -d ' ' -f 1


2. getent ahostsv6 www.google.de | grep STREAM | head -n 1 | cut -d ' ' -f 1


3. getent hosts google.de | head -n 1 | cut -d ' ' -f 1

All commands will resolve an IP address if host still exist. If host points to CNAME it will also get the IP in that case.

The first command returns the resolved IPv4 address

The second command returns the resolved IPv6 address

The third command will return the owners preferred address what may IPv4 or IPv6 address.

Here is a slight variation of the ping approach that takes "unknown host" into account (by piping through stderr) and uses tr to avoid the use of sed regexps:

ping -c1 -t1 -W0 www.example.com 2>&1 | tr -d '():' | awk '/^PING/print $3'

In case it's important to capture the exit value, then the following will work (although less elegant):

ping -c1 -t1 -W0 www.example.com &>/dev/null && ping -c1 -t1 -W0 www.example.com 2>&1 | tr -d '():' | awk '/^PING/print $3'

You could use host:

hostname=example.org

# strips the IP
IP=$( host $hostname | sed -e "s/.* //" )

# checks for errors
if [ $? -ne 0 ] ; then
 echo "Error: cannot resolve $hostname" 1>&2
 exit 1;
fi

To complete Chris Down's answer, and address jfgagne comments about (possibly chained) aliases, here is a solution that :

• takes into account multiple IPs


• takes into account one or more aliases (CNAME)


• does not query /etc/hosts file (in my case I didn't want it); to query it, dbernt's python solution is perfect)


• 
  

  does not use awk/sed

  
  
  

  dig +short www.alias.com | grep -v ".$" | head -n 1
  

  
  

Always returns the first IP address, or empty tring if not resolved. with version of dig :

 $ dig -v
 DiG 9.8.1-P1

 php -r "echo gethostbyname('unix.stackexchange.com');"

nmap -sP 192.168.178.0/24|grep YOUR_HOSTNAME|sed -n 's/.*[(]([0-9.]*)[)].*/1/p'

was the solution I found without DNS server

I would have liked to add this as a comment to Andrew McGregor Re: ping. However it wouldn't let me, so I need to add this as another answer. (If somebody can move it into a comment, feel free to.)

This is another variant, only using ping and grep:

ping -q -c1 -t1 your_host_here | grep -Eo "([0-9]+.?)4"

grep -E for extended regular expression and
grep -o to return only the matching part.
the regexp itself looks for one or multiple digits ([0-9]+) and optionally a dot (.?) four times (4)

here's a Bash recipe I cooked up using other folk's answers — first tries /etc/hosts, then falls back to nslookup:

resolveip() awk 'print $1' )
 if [ -z "$ip" ] 
 then
 ip=$( dig +short "$host" )
 if [ -z "$ip" ]
 then
 echo "unable to resolve '$host'" >&2 
 return 1
 else
 echo "$ip"
 return 0
 fi
 else
 echo "$ip"
 return 0
 fi
 fi

Maybe not the most concise, but it seems to be robust and efficient:

# $(get_host_dns_short "google.com")
#
# Outputs the IPv4 IP Address of a hostname, resolved by DNS. Returns 0 if DNS
# responded successfully; 1 otherwise. Will mask error output.
function get_host_dns_short()
 return 1

This will output a single IPv4 IP, as well as return 1 in the event of failure, while masking stderr output.

You can use it like this:

GOOGLE_IP="$(get_host_dns_short "google.com")"
if [[ $? -eq 0 ]]; then
 echo "Google's IP is $GOOGLE_IP."
else
 echo "Failed to resolve Google's IP."
fi

Google's IP is 216.58.192.46.

If you want an IPv6 address instead, just replace -4 with -6.

dig +noall +answer +nocomments example.com | awk 'printf "%-36st%sn", $1, $5 '

1 line resolve a list of hostname

for LINE in `cat ~/Desktop/mylist`; do a=$(nslookup $LINE | awk '/^Address: / print $1 '); echo $a >> ~/Desktop/ip; done

I am doing this all the time on my Mac which does not have getent. ping seems like a hack. I would like to take /etc/hosts into account as well.

So, I wrote a stupid wrapper for dns.lookup for you who have Node.js installed to provide a CLI:

$ npm install -g lookup-hostname
$ lookup google.com
62.243.192.89

dig is too slow, nslookup is much faster

nslookup google.com | grep -Po 'Address:s*[0-9.]+' | tail -1 | sed -e 's/Address:s*//g'

I don't know the easiest way for a bash-script but if you want to resolve a hostname and see if the host is up, use ping!

ping -a hostname -c 1

Will ping the host one time and resolve the hostname to IP-address.

$ ping -a www.google.com -c 1
PING www.google.com (216.58.211.132) 56(84) bytes of data.
64 bytes from arn09s10-in-f4.1e100.net (216.58.211.132): icmp_seq=1 ttl=54 time=1.51 ms

host -t a cisco.com

this command will show ip address ( will reslove domain to IP )