I want to unset a list of bash variables that have their variable strings stored in an array

Question

I'm working through creating a Dockerfile that calls on a script named start.sh I want to take the environment variables that are passed from the user either by means of docker-compose.yml or docker run -e now what I've wanted to do is something where I have a list of these variables defined dynamically in an array.

## Environment Variables
## Missing Vars off the hop SLACK_HOOK_URL
CONFIG_SETTINGS=(
  AWS_ID
  AWS_SECRET
  BUCKET_REGION
  BUCKET_NAME
  DB_USER
  DB_PASSWORD
  DB_HOSTIP
  DB_PORT
  DB_NAME
)

I only have to unset a subset of the above variables defined in this array.

CONFIG_SECRETS=(
  AWS_ID
  AWS_ID_STR
  AWS_SECRET
  AWS_SECRET_STR
  BUCKET_NAME
  BUCKET_NAME_STR
  DB_USER
  DB_USER_STR
  DB_PASSWORD
  DB_PASSWORD_STR
  DB_HOSTIP
  DB_HOSTIP_STR
  DB_PORT
  DB_PORT_STR
  DB_NAME
  DB_NAME_STR
)

My problem is the following for loop.

## Sanitization section
for i in "${!CONFIG_SECRETS[@]}"; do
  ## Nullify environment variables that contain secrets before launching.
  # echo ${CONFIG_SECRETS[$i]}
  eval $"${CONFIG_SECRETS[$i]}"=$""
  unset $"${CONFIG_SECRETS[$i]}"
  echo \$${CONFIG_SECRETS[$i]} is now to: $"${CONFIG_SECRETS[$i]}"
done

For example, the below is a for loop I created to iterate through these variables and set them.

for i in "${!CONFIG_SETTINGS[@]}"; do
  echo ${CONFIG_SETTINGS[$i]}"_KEY"
  ## Indirect references http://tldp.org/LDP/abs/html/ivr.html
  eval FROM_STRING=\$"${CONFIG_SETTINGS[$i]}_STR"
  eval VALUE_STRING=\$${CONFIG_SETTINGS[$i]}
  eval KEY_STRING=\$"${CONFIG_SETTINGS[$i]}_KEY"
  TO_STRING="$KEY_STRING$VALUE_STRING"
  sed -i '' "s/$FROM_STRING/$TO_STRING/g" ./config.tmpl
done

This modifies the following configuration file.

{
  "aws_id": "YOUR-AWS-ID",
  "aws_secret": "YOUR-AWS-SECRET",
  "bucket_region": "YOUR-BUCKET-REGION",
  "bucket_name": "YOUR-BUCKET-NAME",
  "db_conn": "USER:PASSWORD@tcp(localhost:3306)/DBNAME",
  "slack_hook_url": ""
}

The full context script minus things that are outside of the scope of this question.

#!/bin/bash

## Launch service will tell prism-bin what mode to run in.
LAUNCHMODE="${MODE:-$1}"

## This variable will be what can override default launch args.  I may modify this as I learn more about prism-bin
LAUNCHARGS="${CUSTOM_ARGS:-$2}"

## This is setup this way to handle any situations that might arise from the
## config being JSON and bash not being any good at JSON.
# ## Strings to replace.
AWS_ID_STR="YOUR-AWS-ID"
AWS_SECRET_STR="YOUR-AWS-SECRET"
BUCKET_REGION_STR="YOUR-BUCKET-REGION"
BUCKET_NAME_STR="YOUR-BUCKET-NAME"
DB_USER_STR="USER"
DB_PASSWORD_STR="PASSWORD"
DB_HOSTIP_STR="localhost"
DB_PORT_STR="3306"
DB_NAME_STR="DBNAME"

# Environment Variables/Defaults
## Json sucks in BASH/Shell so you need to add trailing commas intermittently.
## Just pay attention to this.  Also at some point I'll need to make a fringe
## case for handling key/values that aren't included in the default config.
AWS_ID="${AWS_ID:-potato}"
AWS_SECRET="${AWS_SECRET:-potato}"
BUCKET_REGION="${BUCKET_REGION:-potato}"
BUCKET_NAME="${BUCKET_NAME:-potato}"
DB_USER="${DB_USER:-potato}"
DB_PASSWORD="${DB_PASSWORD:-potato}"
DB_HOSTIP="${DB_HOSTIP:-potato}"
DB_PORT="${DB_PORT:-potato}"
DB_NAME="${DB_NAME:-potato}"

## Environment Variables in Array
CONFIG_SETTINGS=(
  AWS_ID
  AWS_SECRET
  BUCKET_REGION
  BUCKET_NAME
  DB_USER
  DB_PASSWORD
  DB_HOSTIP
  DB_PORT
  DB_NAME
)
CONFIG_SECRETS=(
  AWS_ID
  AWS_ID_STR
  AWS_SECRET
  AWS_SECRET_STR
  BUCKET_NAME
  BUCKET_NAME_STR
  DB_USER
  DB_USER_STR
  DB_PASSWORD
  DB_PASSWORD_STR
  DB_HOSTIP
  DB_HOSTIP_STR
  DB_PORT
  DB_PORT_STR
  DB_NAME
  DB_NAME_STR
)

## Sanitization section
# Awaiting someone smarter than me to suggest a method for this.
# https://unix.stackexchange.com/questions/474097/i-want-to-unset-a-list-of-bash-variables-that-have-their-variable-strings-stored
for i in "${CONFIG_SECRETS[@]}"; do
  unset $i
  eval echo \$"${CONFIG_SECRETS[$i]}"=\$${CONFIG_SETTINGS[$i]}
done

Answer 1

This should be a simple loop

#!/bin/bash

UNSET=(a b c)

a=10 b=20 c=30 d=40 e=50

echo Before a=$a b=$b c=$c d=$d e=$e

for i in ${UNSET[@]}
do
  unset $i
done

echo After a=$a b=$b c=$c d=$d e=$e

This results in

Before a=10 b=20 c=30 d=40 e=50
After a= b= c= d=40 e=50

Answer 2

You can dereference variables with !:

$ foo=bar
$ bar=1
$ echo ${!foo}
1

You can't use a variable inside an expansion like that though, so you will probably have to do something really ugly with eval.

Answer 3

I think you've worked yourself into a circle; simply loop over the array and unset the parameter referred to by the loop:

AWS_SECRET='secret_here'
echo Before:
declare -p AWS_SECRET
set|grep AWS_SECRET

for secret in "${CONFIG_SECRETS[@]}"
do
  unset $secret
done

echo After:
declare -p AWS_SECRET
set|grep AWS_SECRET