Bash for loops and hostnames and how to generate them

Question

Why doesn't this work?

NODE_ROOT=node0
INFRA_DOMAIN=example.com
for host in $NODE_ROOT{1..3}.$INFRA_DOMAIN; do echo $host; done

I'm expecting:

node01.example.com
node02.example.com
node03.example.com

However, I get:

.example.com
.example.com
.example.com

How do I do this properly?

score 3 · Accepted Answer · answered Feb 28 '16 at 13:22

3

Replace

$NODE_ROOT{1..3}.$INFRA_DOMAIN

by

${NODE_ROOT}{1..3}.$INFRA_DOMAIN

answered Feb 28 '16 at 13:22

Cyrus

927
1
7
15

score 3 · Answer 2 · edited May 23 '17 at 12:41

The issue with your script is that Bash is not able to interpret $NODE_ROOT{1..3} correctly. To help, you need to enclose the variable in quotes, ", which is generally accepted as 'good practice' in any case. You can also use the "${VARIABLE}"-type syntax to help Bash out too.

For example,

NODE_ROOT=node0
INFRA_DOMAIN=example.com
for host in "$NODE_ROOT"{1..3}."$INFRA_DOMAIN"; do echo $host; done

or

for host in "${NODE_ROOT}"{1..3}."$INFRA_DOMAIN"; do echo $host; done

Further reading:

Stack Overflow question When do we need curly braces in variables using Bash?

score 0 · Answer 3 · answered Feb 28 '16 at 08:35

0

You can simply modify your script to read:

NODE_ROOT=node0
INFRA_DOMAIN=example.com
for n in {1..3}; do echo ${NODE_ROOT}${n}.${INFRA_DOMAIN}; done

answered Feb 28 '16 at 08:35

Khaled

36,533
8
72
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Bash for loops and hostnames and how to generate them

3 Answers3