Powershell - add variables inside a json string

There are various ways to solve your problem, but perhaps the easiest approach is to use PowerShell's string interpolation:

• use a double-quoted (expandable) string overall to enable interpolation of embedded variable references and subexpressions ($(...)).

• escape embedded " chars. as `" (using backticks)

• disambiguate variable references by enclosing the variable name in {...}.

Simplified example:

$variable='111'
# -> verbatim:  {"Version": "arn:aws:iam::111:role/xxxxxx"}
"{`"Version`": `"arn:aws:iam::${variable}:role/xxxxxx`"}"

Note that enclosing variable names in {...} in interpolated strings is only necessary if the following char. could be misinterpreted as part of the variable name.
A : following the variable name - as is the case here - is such a case, because PS variables can have a scope specifier preceding the variable name that is separated from the variable name with :, such as in $env:USERNAME.

DAXaholic's helpful answer shows an alternative based on PowerShell's -f operator, which is essentially the same as the .NET framework's String.Format method; as such:

• it introduces additional complexity, such as needing to know what its escaping rules are ({ chars. must be escape as {{, and how to format its arguments specified on the RHS of -r ({0} refers to the 1st RHS argument, ...)

• on the flip side, -f offers many sophisticated formatting options.

Also, consider use of the Convert*-Json cmdlets his answer demonstrates: even though they're less performant, they ultimately make manipulation of JSON much easier and more robust.

Alternatives in the realm of native PowerShell code:

• String concatenation with the binary + operator:

'{"Version": "arn:aws:iam::' + $variable + ':role/xxxxxx"}}'

• String templating with $ExecutionContext.InvokeCommand.ExpandString():

$variable='111'    
$tmpl = '{"Version": "arn:aws:iam::${variable}:role/xxxxxx"}}' # string template *literal*
$ExecutionContext.InvokeCommand.ExpandString($tmpl) # performs on-demand interpolation

Another solution would be

$jsonfile = '{{"Version": "2012-10-17","Statement": {{"Effect": "Allow","Action": "sts:AssumeRole","Resource": "arn:aws:iam::{0}:role/xxxxxx"}}}}' -f $variable  

So you have to escape the braces with another brace but in your case you have fewer braces than quotes so it is "less obfuscation" :)

In your case, maybe the simplest solution is just concatenating the strings together instead of using string formatting / interpolation.

In addition you could also go the way with the JSON cmdlets:

$jsonfile | 
    ConvertFrom-Json | 
    % { $_.Statement.Resource = "arn:aws:iam::${variable}:role/xxxxxx"; $_ } | 
    ConvertTo-Json

You can use a 'Here-string'. It is declared just like a regular string except it has an @ on each end. For example:

$jsonfile = @"
  {
    "Version": "2012-10-17",
    "Statement": {
      "Effect": "Allow", 
      "Action": "sts:AssumeRole",
      "Resource": "arn:aws:iam::$variable:role/xxxxxx"}
  }
"@

However, in this particular example, the :role part confuses Powershell a bit. So you need to escape the colon like $variable`:role or wrap the variable like $($variable):role or ${variable}:role.