Find and Replace Nested JSON Values with Powershell - json

Question

I have an appsettings.json file that I would like to transform with a PowerShell script in a VSTS release pipeline PowerShell task. (BTW I'm deploying a netstandard 2 Api to IIS). The JSON is structured like the following:
{
"Foo": {
"BaseUrl": "http://foo.url.com",
"UrlKey": "12345"
},
"Bar": {
"BaseUrl": "http://bar.url.com"
},
"Blee": {
"BaseUrl": "http://blee.url.com"
}
}
I want to replace BaseUrl and, if it exists, the UrlKey values in each section which are Foo, Bar and Blee. (Foo:BaseUrl, Foo:UrlKey, Bar:BaseUrl, etc.)
I'm using the following JSON structure to hold the new values:
{
"##{FooUrl}":"$(FooUrl)",
"##{FooUrlKey}":"$(FooUrlKey)",
"##{BarUrl}":"$(BarUrl)",
"##{BleeUrl}":"$(BleeUrl)"
}
So far I have the following script:
# Get file path
$filePath = "C:\mywebsite\appsettings.json"
# Parse JSON object from string
$jsonString = "$(MyReplacementVariablesJson)"
$jsonObject = ConvertFrom-Json $jsonString
# Convert JSON replacement variables object to HashTable
$hashTable = #{}
foreach ($property in $jsonObject.PSObject.Properties) {
$hashTable[$property.Name] = $property.Value
}
# Here's where I need some help
# Perform variable replacements
foreach ($key in $hashTable.Keys) {
$sourceFile = Get-Content $filePath
$sourceFile -replace $key, $hashTable[$key] | Set-Content $filePath
Write-Host 'Replaced key' $key 'with value' $hashTable[$key] 'in' $filePath
}

Answer 1

Why are you defining your replacement values as a JSON string? That's just going to make your life more miserable. If you're defining the values in your script anyway just define them as hashtables right away:
$newUrls = #{
'Foo' = 'http://newfoo.example.com'
'Bar' = 'http://newbaz.example.com'
'Blee' = 'http://newblee.example.com'
}
$newKeys = #{
'Foo' = '67890'
}
Even if you wanted to read them from a file you could make that file a PowerShell script containing those hashtables and dot-source it. Or at least define the values as lists of key=value lines in text files, which can easily be turned into hashtables:
$newUrls = Get-Content 'new_urls.txt' | Out-String | ConvertFrom-StringData
$newKeys = Get-Content 'new_keys.txt' | Out-String | ConvertFrom-StringData
Then iterate over the top-level properties of your input JSON data and replace the nested properties with the new values:
$json = Get-Content $filePath | Out-String | ConvertFrom-Json
foreach ($name in $json.PSObject.Properties) {
$json.$name.BaseUrl = $newUrls[$name]
if ($newKeys.ContainsKey($name)) {
$json.$name.UrlKey = $newKeys[$name]
}
}
$json | ConvertTo-Json | Set-Content $filePath
Note that if your actual JSON data has more than 2 levels of hierarchy you'll need to tell ConvertTo-Json via the parameter -Depth how many levels it's supposed to convert.
Side note: piping the Get-Content output through Out-String is required because ConvertFrom-Json expects JSON input as a single string, and using Out-String makes the code work with all PowerShell versions. If you have PowerShell v3 or newer you can simplify the code a little by replacing Get-Content | Out-String with Get-Content -Raw.

Answer 2

Thank you, Ansgar for your detailed answer, which helped me a great deal. Ultimately, after having no luck iterating over the top-level properties of my input JSON data, I settled on the following code:
$json = (Get-Content -Path $filePath) | ConvertFrom-Json
$json.Foo.BaseUrl = $newUrls["Foo"]
$json.Bar.BaseUrl = $newUrls["Bar"]
$json.Blee.BaseUrl = $newUrls["Blee"]
$json.Foo.Key = $newKeys["Foo"]
$json | ConvertTo-Json | Set-Content $filePath
I hope this can help someone else.

Answer 3

To update values of keys at varying depth in the json/config file, you can pass in the key name using "." between the levels, e.g. AppSettings.Setting.Third to represent:
{
AppSettings = {
Setting = {
Third = "value I want to update"
}
}
}
To set the value for multiple settings, you can do something like this:
$file = "c:\temp\appSettings.json"
# define keys and values in hash table
$settings = #{
"AppSettings.SettingOne" = "1st value"
"AppSettings.SettingTwo" = "2nd value"
"AppSettings.SettingThree" = "3rd value"
"AppSettings.SettingThree.A" = "A under 3rd"
"AppSettings.SettingThree.B" = "B under 3rd"
"AppSettings.SettingThree.B.X" = "Z under B under 3rd"
"AppSettings.SettingThree.B.Y" = "Y under B under 3rd"
}
# read config file
$data = Get-Content $file -Raw | ConvertFrom-Json
# loop through settings
$settings.GetEnumerator() | ForEach-Object {
$key = $_.Key
$value = $_.Value
$command = "`$data.$key = $value"
Write-Verbose $command
# update value of object property
Invoke-Expression -Command $command
}
$data | ConvertTo-Json -Depth 10 | Out-File $file -Encoding "UTF8"