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set a variable with a variable name

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# 1  
Old 11-01-2009
Question set a variable with a variable name
Hi there,

I can display a variable with a variable name:
Code:
localhost:~# a=1
localhost:~# b=a
localhost:~# echo $b
a
localhost:~# echo ${!b}
1

But how can I set a variable with a variable name?
In the following example, I want to set a = 1:
Code:
localhost:~# b=a
localhost:~# $b=1
-bash: a=1: command not found

Can anyone help me?
Thanks in advance
Santiago
# 2  
Old 11-01-2009
Hi.

Using eval:

Code:
b=a
eval $b=1
echo $a
1

# 3  
Old 11-01-2009
Quote:
Originally Posted by chebarbudo
Hi there,

I can display a variable with a variable name:
Code:
localhost:~# a=1
localhost:~# b=a
localhost:~# echo $b
a
localhost:~# echo ${!b}
1


Note that that is not portable; it is specific to bash.

The portable syntax is:

Code:
eval "echo \${$b}"

Quote:
But how can I set a variable with a variable name?
In the following example, I want to set a = 1:
Code:
localhost:~# b=a
localhost:~# $b=1
-bash: a=1: command not found

Code:
eval "$b=1"

# 4  
Old 11-02-2009
Thanks very much scottn and cfajohnson, it all works.

By the way, I just heard about the usage of bits as rewards for people who help others on the forum. It looks like I already earned some. It's a bit embarassing to ask but what is a reasonable number of bits to reward someone for helping me on that subject?
Thanks for helping me being a better programmer and a more civilized forum user.
# 5  
Old 11-02-2009
You seemed civilised to me anyway ;-)

I try to give bits on how useful I find the answer is to me (even though I didn't ask the question).

Save your bits for a rainy day.
Last edited by Scott; 11-02-2009 at 11:45 AM..
# 6  
Old 11-03-2009
Hey masters,
What's wrong with my syntax?
Code:
r29829:~# cat conf
A=1
B=2
C=3
r29829:~# cat testconf.sh
#!/bin/bash
cat conf | while IFS="=" read lvalue rvalue; do
        eval $lvalue=$rvalue
done
echo "-$A-$B-$C-"
r29829:~# ./testconf.sh
----

I was expecting the following output:
Code:
r29829:~# ./testconf.sh
-1-2-3-

Did I do something wrong?
Thanks for your help.
# 7  
Old 11-03-2009
Code:
#!/bin/bash
while IFS="=" read lvalue rvalue; do
 eval $lvalue=$rvalue
done < conf
echo "-$A-$B-$C-"


-1-2-3-

Last edited by Scott; 11-03-2009 at 06:56 PM..
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