Ykhjuy

I have to use environment vars in my bash shell and:

• 
  echo $ENV resolves to DEV, STAGE or PRD depending upon the stack.


• 
  echo $DEV_ACCOUNT resolves to a number e.g. echo $DEV_ACCOUNT gives 12345678
  

I need to use echo $ENV_ACCOUNT in a command which should resolve to 12345678 but it is resolving to DEV_ACCOUNT instead of 12345678.

The command I am using:

aws events put-targets --rule {{ stack_name | lower }}-hello-world 

    --targets "Id"="1","Arn"="arn:aws:lambda:us-west-2:$ENV_ACCOUNT:function:hello-world"

The $ENV_ACCOUNT is resolving to DEV_ACCOUNT instead of 12345678.
The expected output is:

aws events put-targets --rule {{ stack_name | lower }}-hello-world 

    --targets "Id"="1","Arn"="arn:aws:lambda:us-west-2:12345678:function:hello-world"

What am I doing wrong?

Note that uppercase variable names are not generally safe to use. $ENV, for example, is special in many shells. In these shells, its value should be the pathname of a file that will be sourced before starting certain types of shells. The bash shell uses $ENV in POSIX mode.

So, in bash:

declare -A account

account["develop"]=12345678

account["staging"]=9128312

account["production"]=123123



mode=$run_mode



aws events put-targets 

    --rule {{ stack_name | lower }}-hello-world 

    --targets "Id"="1","Arn"="arn:aws:lambda:us-west-2:${account[$mode]}:function:hello-wolrd"

This sets up an associative array, account, that holds the data for development, staging and production modes. It then defines the mode that we're using and executes the command with the correct data from the account array. The run_mode variable is assumed to be an environment variable containing one of the strings develop, staging or production.

Associative arrays were introduced in bash 4.0.

I have used your aws command as you wrote it (except for adding newlines and my account variable), even though the {{ stack_name | lower }}-hello-world probably does not de what you'd expect it to (it would try to execute lower as a command). Since I don't know aws, I don't know what it should look like, but it should probably be quoted.

I will repeat what Kusalananda said about not using ALLCAPS for variable names in shell scripts. That is generally a bad idea and can cause issues when your variable names collide with default environment variables. And I also agree that the best way to do this is to use an associative array as he describes in his answer.

That said, the specific problem you are facing is because $ENV_ACCOUNT is being read as $ENV and the string _ACCOUNT. So $ENV is being expanded to DEV and $ENV_ACCOUNT becomes DEV_ACCOUNT. If you insist on doing it this (wrong) way instead of using an array, you will need to do something like this:

varname="$env"_account

aws events put-targets --rule {{ stack_name | lower }}-hello-world 

    --targets "Id"="1","Arn"="arn:aws:lambda:us-west-2:${!varname}:function:hello-world"

The ${!var} syntax will expand to the value of a variable named var. For example:

$ foo="foovar"

$ bar=foo

$ echo ${!bar}

foovar

Seriously though, just don't do this. It is complicated, cumbersome, hard to read, harder to maintain and an associative array will just solve all of these issues for you.