How to properly store the output of host command in bash

Question

I'm trying to store ip addresses given by host, but host actually gives a string saying host-name has address ip-address as many times as many addresses it finds. So my question is can I somehow access the addresses only, without splitting strings and looking for ip addresses? What I've tried so far looks like this

ip=$(host "$candidate")

IFS="s " read -ra ADDR <<< "$ip"
for i in "${ADDR[@]}"; do
    echo "$i"
done

where $candidate holds the host name, but I couldn't really put it to work. Any ideas?

if you have ssh access keys set from source/target candidate server for password less access, you can do: ip=$(ssh user@$candidate "hostname -i") — AKS
– AKS, Commented Sep 16, 2014 at 22:18

jordanm · Accepted Answer · 2014-09-16 22:35:42Z

2

You can use a different DNS lookup tool, such as dig:

$ foo=($(dig google.com +short))
$ printf '%s\n' "${foo[@]}"
74.125.228.196
74.125.228.206
74.125.228.200
74.125.228.198
74.125.228.193
74.125.228.192
74.125.228.199
74.125.228.197
74.125.228.201
74.125.228.195
74.125.228.194

If you must use host, then you will have to do string splitting:

foo=()
while read -r _ _ _ addr; do
    foo+=("$addr")
done < <(host -t A google.com)
printf '%s\n' "${foo[@]}"

answered Sep 16, 2014 at 22:35

jordanm

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1 Comment

Charles Duffy Over a year ago

With bash 4 or newer, readarray is available: readarray -t foo < <(dig google.com +short); this skips some bugs your first answer has around glob expansion and odd IFS values. That said, +1 for suggesting dig +short.

David C. Rankin · Accepted Answer · 2014-09-16 22:58:48Z

1

You can isolate the IP address using parameter expansion/substring extraction as follows:

#!/bin/bash

while read -r line; do 
    array+=( ${line##* } )      # substring extraction for IP only
done < <(host -t A google.com)

for i in ${array[@]}; do
    echo "$i"
done

Output:

$ bash getip.sh
173.194.115.36
173.194.115.35
173.194.115.40
173.194.115.37
173.194.115.34
173.194.115.39
173.194.115.41
173.194.115.46
173.194.115.33
173.194.115.38
173.194.115.32

You can accomplish the same thing with string substitution:

    array+=( ${line//*\ /} )      # string substitution for IP only

answered Sep 16, 2014 at 22:58

David C. Rankin

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4 Comments

Charles Duffy Over a year ago

Quote your expansions -- for i in "${array[@]}", or else you've written an equivalent to for i in ${array[*]}.

Charles Duffy Over a year ago

similarly: array+=( "${line##* }" ), if you want one array entry per line.

Charles Duffy Over a year ago

Alternately: while IFS=' ' read -r ip _; do array+=( "$ip" ); done strips off everything after the first ` ` implicitly, without the PE needed, by putting that content into _.

David C. Rankin Over a year ago

Yes, agree, but the output from hosts is of the form google.com has address 173.194.115.41 which would lead to a read -r _ _ _ IP as indicated in the other answer.

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