Powershell variable expansion in single quoted string

Question

I need to build a JSON variable that contains another JSON formatted content which should be formatted as a string. I'm putting the inner JSON into single quote so it wont get parsed along with the outer JSON. The inner JSON contains a variable that should be extended. Unfortunately, the single quotes prevent this.
Example:

$link = "http://www.google.de"
$event = @{
   var1 = "sys"
   var2 = "yadda"
   inner_json = '"System": {"link":"$link"}}'
}
$json = $event | ConvertTo-Json

The variable $inner_json must be embedded as a string. Is there any way to enforce the expansion of $link within the single quotes? Any other idea how to solve this problem? Any help is apprectiated.
edit: I would be expecting the inner_json like this:

{"var1":"sys", "var2":"yadda", "inner_json": "{\"System\": {\"link\":\"google.de\"}}"}

Can you post the json you're expecting from your example $event | ConvertTo-Json? You can possibly solve this by using nested hashtables, but seeing your desired json would make sure... — mclayton
– mclayton, Commented Jan 20, 2020 at 8:36
I would be expecting: {"var1":"sys", "var2":"yadda", "inner_json": "{\"System\": {\"link\":\"google.de\"}}"} — Royce
– Royce, Commented Jan 20, 2020 at 10:43

iRon · Accepted Answer · 2020-01-20 11:53:44Z

5

If you prepare the object (using a HashTable or PSCustomObject), variables (starting with a $, including $var1, $inner_json) will be automatically expanded anyway.
I think you want to do this:

$link = "http://www.google.de"
$event = @{
    var1 = 'sys'
    var2 = 'yadda'
    inner_json = @{
        System = @{
            link = $link
        }
    }
}
$event | ConvertTo-Json

{
  "inner_json": {
    "System": {
      "link": "http://www.google.de"
    }
  },
  "var2": "yadda",
  "var1": "sys"
}

Based on the added expectation:
_{*Note:

Double quotes are automatically escaped with a backslash (\) in json.

To escape a double quote in PowerShell, use the backtick: (`)}

$link = "http://www.google.de"
$event = @{
    var1 = 'sys'
    var2 = 'yadda'
    inner_json = "{`"System`": {`"link`":`"$Link`"}}"
}
$event | ConvertTo-Json

{
  "inner_json": "{\"System\": {\"link\":\"http://www.google.de\"}}",
  "var2": "yadda",
  "var1": "sys"
}

But it is better to stay away from fabricating a Json string (including the inner Json string) and also create the inner Json from an object and literally embed that string into the outer Json:

$link = "http://www.google.de"
$event = @{
    var1 = 'sys'
    var2 = 'yadda'
    inner_json = @{System = @{link = $Link}} | ConvertTo-Json -Compress
}
$event | ConvertTo-Json

{
  "inner_json": "{\"System\":{\"link\":\"http://www.google.de\"}}",
  "var2": "yadda",
  "var1": "sys"
}

edited Jan 20, 2020 at 11:53

answered Jan 20, 2020 at 9:57

iRon

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3 Comments

Royce Over a year ago

Makes sense, but the inner json would be parsed. see my comment above how the outer json should look like

mclayton Over a year ago

note that if order of properties is important you can create an OrderedDictionary instead of a hashtable with $event = [ordered] @{ ... }

Royce Over a year ago

Thanks a lot! the convertto-json on the inner_json did the trick!

mklement0 · Accepted Answer · 2020-01-20 14:35:21Z

1

iRon's helpful answer contains the best solution for your use case.

To answer your question as suggested by its title, which is really a different use case:

You can use $ExecutionContext.InvokeCommand.ExpandString() to interpret verbatim strings as expandable ones on demand:

# A variable to reference in the template string below.
$link = 'http://example.org'

# A verbatim string that is to be interpreted as an expandable one later, on demand:
$template = '"System": {"link":"$link"}}'

# Expand the template, using the current values of the variables referenced:
$ExecutionContext.InvokeCommand.ExpandString($template)

The above yields a string with the following verbatim content; note how the value of $link was expanded:

"System": {"link":"http://example.org"}}

answered Jan 20, 2020 at 14:35

mklement0

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1 Comment

Royce Over a year ago

This is a more generic usecase and also works as a solution for my issue. Thanks!

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