eval not working in shellscript - shell

Question

I am trying to get the value of a variable to be selected by name at runtime, using eval, but I don't get its value if - (hyphen) is in the name.
ENV=dev
REGION=us-east-1
DBUSERNAME=DB_USER_${ENV}_$REGION
DBPASSWORD=DB_PASS_${ENV}_$REGION
eval "USERNAME=\${${DBUSERNAME}}"
eval "PASSWORD=\${${DBPASSWORD}}"
echo USERNAME=$USERNAME
echo PASSWORD=$PASSWORD
RESULT
echo USERNAME=east-1
echo PASSWORD=east-1
EXPECTED RESULT
echo USERNAME=DB_USER_dev_us-east-1
echo PASSWORD=DB_USER_dev_us-east-1
It's working fine if there is no hyphen present in the name.

Answer 1

Investigation
We can see what's happening by running this in shell with -x option to trace execution:
$ sh -x ./36332134.sh
+ ENV=dev
+ REGION=us-east-1
+ DBUSERNAME=DB_USER_dev_us-east-1
+ DBPASSWORD=DB_PASS_dev_us-east-1
+ eval USERNAME=${DB_USER_dev_us-east-1}
+ USERNAME=east-1
+ eval PASSWORD=${DB_PASS_dev_us-east-1}
+ PASSWORD=east-1
+ echo USERNAME=east-1
USERNAME=east-1
+ echo PASSWORD=east-1
PASSWORD=east-1
Notice that eval USERNAME=${DB_USER_dev_us-east-1} gives us USERNAME=east-1. That's parameter expansion in effect, as described in the Bash manual:
When not performing substring expansion, using the forms documented below (e.g., :-), bash tests for a parameter that is unset
or null. Omitting the colon results in a test only for a parameter
that is unset.
${parameter:-word}
Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter
is substituted.
Since $DB_USER_dev_us is unset, then the expansion of ${DB_USER_dev_us-east-1} is east-1.
Workarounds
Shell doesn't allow - in variable names (including environment variables). I guess DB_USER_dev_us-east-1 was set by some non-shell program? In which case, you'll need a similar non-shell program to retrieve it, I think. I tested quoting the -, but to no avail.
If you can use Bash as your shell, you might want to use an associative array instead of composing variable names.
If you are able to change the environment variables, you might consider changing the - to (say) _, then using (Bash) ${REGION//-/_} or (otherwise) tr to transform the name:
REGION="${REGION//-/_}" # Bash
REGION="$(echo "$REGION"|tr - _)" # POSIX

Answer 2

You are evaluating/expanding a few too many times.
Toby's answer is exactly correct (and shows the proper debugging technique for this sort of issue) but the solution to the problem is to unwrap one level of expansion.
You wrote
eval "USERNAME=\${${DBUSERNAME}}"
which becomes
eval "USERNAME=\${DB_USER_dev_us-east-1}"
which then gets run through eval as
USERNAME=${DB_USER_dev_us-east-1}
which becomes
USERNAME=east-1
but you wanted to stop after the first expansion. That is
eval "USERNAME=\${DB_USER_dev_us-east-1}"
has already performed the expansion you wanted and gotten you the result you needed. So you don't want the \${...} bit or eval. Just
USERNAME=DB_USER_dev_us-east-1
which you get from
USERNAME=${DBUSERNAME}
Unless I've missed something or your example isn't accurate.

Answer 3

As they have explained the problem, here is what you can do
$> more a.sh
ENV=dev
REGION=us-east-1
DBUSERNAME=DB_USER_${ENV}_$REGION
DBPASSWORD=DB_PASS_${ENV}_$REGION
eval "USERNAME=${DBUSERNAME}"
eval "PASSWORD=${DBPASSWORD}"
echo USERNAME=$USERNAME
echo PASSWORD=$PASSWORD
Results
$> ./a.sh
USERNAME=DB_USER_dev_us-east-1
PASSWORD=DB_PASS_dev_us-east-1