Export variable as contents of another variable

jnojr · 05-08-2012, 08:49 AM

I'm sure this is ridiculously easy, but my brain is seizing on it

If we have:

A=1
B=2
C=3

X=`some command that will return A, B, or C`

How do I get a variable that will look at $X, see A B or C, and return the value of $A, $B, or $C?

jnojr · 05-08-2012, 08:51 AM

N/M

eval newvar=\$$X

grail · 05-08-2012, 10:15 AM

Please do not use eval if you can help it (search the net for many reasons why not):

Code:

A=1

X=A

echo ${!X}

David the H. · 05-08-2012, 02:48 PM

Indirect variable reference is so awkward and untransparent. You're also limited to only using strings that match proper variable syntax; only letters, digits, and the underscore are allowed, and it can't begin with a digit.

Assuming bash or another shell that supports them, an associative array would be better. Then you can use any arbitrary string:

Code:

#!/bin/bash

declare -A array

array=( [A]=1 [B]=2 [C]=3 )


for x in A B C ; do

	echo "The value for entry $x is: ${array[$x]}"

done

How can I use variable variables (indirect variables, pointers, references) or associative arrays?
http://mywiki.wooledge.org/BashFAQ/006

BTW, environment variables are generally all upper-case. So while not critical, it's good practice to keep your own user variables in lower-case or mixed-case, to help differentiate them.