How to use variables in a range from 1 to 200 in loop on bash

Question

I have script for getting some records:

#!/bin/bash 

host_start=test
domain=test.com

for host in "${host_start}"{1..200}."$domain";
do
    address=`dig +short $host`
    echo "$address = $host"
done

In this case, everything is OK. I have:

192.168.1.1 = test1.test.com
192.168.1.2 = test2.test.com
192.168.1.3 = test3.test.com
...
...
...
etc ...

But instead of the literal {1..200}, I want to use variables in the start of my script. I did this:

t1=1
t2=200
for host in "${host_start}"{$t1..$t2}."$domain";
do 
...

In this case, I get an error:

dig: 'test{1..200}.test.com' is not a legal name (empty label)

Where is my error? How do I fix it?

@chepner I marked the one your dupe as a dupe of my dupe, if you want to hammer that one too. — Mad Physicist, May 16 '17 at 13:36

score 3 · Accepted Answer · answered May 16 '17 at 13:24

3

Brace expansion happens before variable expansion, so you can't use it with variables. Use a loop or the seq command.

for ((i=t1; i<=t2; i++)) ; do
    host=$host_start$i.$domain

or

for i in $( seq $t1 $t2 ) ; do
    host=$host_start$i.$domain

answered May 16 '17 at 13:24

choroba

231,213
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@MadPhysicist: `seq` is a nonstandard utility, so if strict POSIX compliance is a must, it should be avoided; it is, however, both widely available, widely used, and continues to provide useful functionality. – mklement0 May 16 '17 at 13:34
Fair enough. Comment rescinded. – Mad Physicist May 16 '17 at 13:36

score 2 · Answer 2 · answered May 16 '17 at 13:25

2

You should probably do:

for ((i=t1; i <= t2; i++)); do 
   host="${host_start}"$i."$domain"
   ...
done

answered May 16 '17 at 13:25

William Pursell

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How to use variables in a range from 1 to 200 in loop on bash

2 Answers2