Using variables as part of variable name in unix [duplicate]

Question

I want to name variable as a_${v}.

for example : v can be 2013 2014

I am now declaring a variable to a_${v}

a_${v}=hI # a_2013 should be Hi

v=2014

so a_${v}=Hello # a_2014 should be Hello

I tried using eval command though it is not throwing error while assigning a value but I am not able to extract the value of variable name

$ v=2013

$ eval a_${v}=Hi


$ v=2014

$ eval a_${v}=Hello

echo ${a_${v}}

is not working.. :(

I am using bash and I don't want to change the variable name i.e dn't want to assign the value to another value

Answer 1

In bash you can do the below (note the exclamation mark syntax in the last line):

#!/bin/bash

a_2014='hello 2014'
year=2014
varname=a_${year}
echo ${!varname}

Answer 2

Parameter expansion is not recursive, therefore the text ${a_${v}} is really The contents of the variable whose name is 'a_${v}', and the shell complains that this variable name is not valid.

You can achieve recursive expansion with the eval command, as in

eval printf '%s\n' "\${a_${v}}"

To increase the readability and maintainability of your shell scripts, you should limit the use of such constructs and wrap them in appropriate structures. See rc.subr provided on FreeBSD systems for an example.