Use of variable name in shell script

Question

First of all I'm sorry for a probable bad title, but I don't even know what to call this.

I'm trying the following:

#!/bin/sh
VAR1="28-00000202070c"
VAR2="28-0000018776d3"
VAR3="28-0000033a6174"

for sensor in VAR1 VAR2 VAR3
do
 echo "$sensor:  $$sensor"
done

The expected output would be:

VAR1: 28-00000202070c

VAR2: 28-0000018776d3

VAR3: 28-0000033a6174

The real output is:

VAR1: 24038sensor

VAR2: 24038sensor

VAR3: 24038sensor

and the strange prefix number keeps growing...

VAR1: 24039sensor

VAR2: 24039sensor

VAR3: 24039sensor

...

I'd like to ask:

1) What are the correct terms/keywords that describe what I'm trying to do here

2) How to get to the expected output

Thanks, Joaoabs

fedorqui · Accepted Answer · 2013-12-23 11:20:51Z

3

This is something that sh does not support, while bash does.

The correct syntax you should use is:

echo "$sensor ${!sensor}"

Test

$ cat a
#!/bin/bash                 <----- note I changed /bin/sh to /bin/bash

VAR1="28-00000202070c"
VAR2="28-0000018776d3"
VAR3="28-0000033a6174"

for sensor in VAR1 VAR2 VAR3
do
 echo "$sensor ${!sensor}"
done

$ ./a
VAR1 28-00000202070c
VAR2 28-0000018776d3
VAR3 28-0000033a6174

answered Dec 23, 2013 at 11:20

fedorqui

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