Powershell - add variables inside a json string

Question

I have the following json code in my powershell script. I set the $variable to 1111111111

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

The output gives ....arn:aws:iam::$variable:role/xxxxxx..... instead of ....arn:aws:iam::1111111111:role/xxxxxx

The problem is that I must use the single quote for the json string otherwise I will get an error. If I use single quote I wont be able to put the variables inside the string. How do I workaround this problem?

Answer 1

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

• use a double-quoted 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:

PS> $variable='111'
PS> "{`"Version`": `"arn:aws:iam::${variable}:role/xxxxxx`"}}"
{"Version": "arn:aws:iam::111: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.

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DAXaholic's helpful answer shows an alternative based on PowerShell's binary -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.

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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