[SOLVED] How to evaluate the value of a variable ?

915086731 · 08-11-2011, 01:43 AM

How to evaluate the value of a variable ?
For example:

a=var
$a=value !!!error happens!!!

I want to evaluate var=value, how to realize it?
Thanks!

16pide · 08-11-2011, 03:15 AM

what language or script language???

in bash script language, you can try something like this:

Code:

#!/bin/bash
a=12
if [[ "$a" -eq 12 ]]
then
  echo "is equal"
else
  echo "is not equal"
fi

915086731 · 08-11-2011, 03:29 AM

Thanks , maybe you don't understand me.
I am using linux bash.

Code:

a=var
$a=value !!!error happens!!!

I want the following result:

Code:

$echo $a
var
$echo $var
value

So I want the value of $a to be a variable, and it can be valued.

eSelix · 08-11-2011, 04:35 AM

There is no such construct in bash as I known, you may use "eval" to achieve this behavior:

Code:

a=var
eval $a=value

David the H. · 08-11-2011, 05:03 AM

I'd like to know what your real purpose is, because this has all the hallmarks of an XyProblem.

You want to evaluate a variable, so that you can use the value as the name of another variable. This can't generally be done directly. It can be done with eval, as above, but the use of eval is risky, not recommended, and probably not necessary.

Chances are that what you want to do can better be done with an array, or an indirect reference, or something similar, but we'd need to hear the details first.

At the very least, the above example can be done reasonably more safely using declare instead of eval.

Code:

a=var
declare $a=value