set a variable with a variable name

chebarbudo · #1 (**permalink**) 3 Weeks Ago

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

scottn · #2 (**permalink**) 3 Weeks Ago

Hi.

Using eval:

Code:

b=a
eval $b=1
echo $a
1

cfajohnson · #3 (**permalink**) 3 Weeks Ago

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"

chebarbudo · #4 (**permalink**) 3 Weeks Ago

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.

scottn · #5 (**permalink**) 3 Weeks Ago

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.

chebarbudo · #6 (**permalink**) 2 Weeks Ago

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.

scottn · #7 (**permalink**) 2 Weeks Ago

Code:

#!/bin/bash
while IFS="=" read lvalue rvalue; do
 eval $lvalue=$rvalue
done < conf
echo "-$A-$B-$C-"


-1-2-3-

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Bits Awarded / Charged to scottn for this Post
Date	User	Comment	Amount
3 Weeks Ago	chebarbudo	Thanks for your help	100

Bits Awarded / Charged to cfajohnson for this Post
Date	User	Comment	Amount
3 Weeks Ago	chebarbudo	A very complete answer, thanks for your time	150

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