Modify YML files with PowerShell

In this short post, I’ll share a simple script to modify the YML files. You can also use the script in the CI/CD pipelines, an example for Azure DevOps is below.

To read the YML file we will use powershell-yaml module, which you can install and active like this:

Install-Module -Name powershell-yaml
Import-Module powershell-yaml

1 2	Install-Module -Name powershell-yaml Import-Module powershell-yaml

Here is our sample YML file that we will use in our little demo:

header: "This is header"
data:
   param1: "Awesome parameter"
   param2: "will be replaced"
footer:
   title: "Footer Title"
   body: "will be replaced"

header: "This is header"

data:

param1: "Awesome parameter"

param2: "will be replaced"

footer:

title: "Footer Title"

body: "will be replaced"

And here is a PowerShell script, that will modify the above YML file. It contains some comments, so you can read through.

# Arguments that get passed to the script when running it
param (
    [Parameter(Position=1)]
    $Param2,
    [Parameter(Position=2)]
    $FooterBody
)

# Install and import the `powershell-yaml` module
# Install module has a -Force -Verbose -Scope CurrentUser arguments which might be necessary in your CI/CD environment to install the module
Install-Module -Name powershell-yaml -Force -Verbose -Scope CurrentUser
Import-Module powershell-yaml

# LoadYml function that will read YML file and deserialize it
function LoadYml {
    param (
        $FileName
    )
	# Load file content to a string array containing all YML file lines
    [string[]]$fileContent = Get-Content $FileName
    $content = ''
    # Convert a string array to a string
    foreach ($line in $fileContent) { $content = $content + "`n" + $line }
    # Deserialize a string to the PowerShell object
    $yml = ConvertFrom-YAML $content
    # return the object
    Write-Output $yml
}

# WriteYml function that writes the YML content to a file
function WriteYml {
    param (
        $FileName,
        $Content
    )
	#Serialize a PowerShell object to string
    $result = ConvertTo-YAML $Content
    #write to a file
    Set-Content -Path $FileName -Value $result
}

# Loading yml, setting new values and writing it back to disk
$yml = LoadYml "sample.yml"
$yml.data.param2 = $Param2
$yml.footer.body = $FooterBody
WriteYml "sample.yml" $yml

# Arguments that get passed to the script when running it

param (

[Parameter(Position=1)]

$Param2,

[Parameter(Position=2)]

$FooterBody

)

# Install and import the `powershell-yaml` module

# Install module has a -Force -Verbose -Scope CurrentUser arguments which might be necessary in your CI/CD environment to install the module

Install-Module -Name powershell-yaml -Force -Verbose -Scope CurrentUser

Import-Module powershell-yaml

# LoadYml function that will read YML file and deserialize it

function LoadYml {

param (

$FileName

)

# Load file content to a string array containing all YML file lines

[string[]]$fileContent = Get-Content $FileName

$content = ''

# Convert a string array to a string

foreach ($line in $fileContent) { $content = $content + "`n" + $line }

# Deserialize a string to the PowerShell object

$yml = ConvertFrom-YAML $content

# return the object

Write-Output $yml

}

# WriteYml function that writes the YML content to a file

function WriteYml {

param (

$FileName,

$Content

)

#Serialize a PowerShell object to string

$result = ConvertTo-YAML $Content

#write to a file

Set-Content -Path $FileName -Value $result

}

# Loading yml, setting new values and writing it back to disk

$yml = LoadYml "sample.yml"

$yml.data.param2 = $Param2

$yml.footer.body = $FooterBody

WriteYml "sample.yml" $yml

Save both files to the same folder. Now when you run .\script.ps1 -Param2 "Param value" -FooterBody "Footer value" your sample YML file is modified:

data:
  param1: Awesome parameter
  param2: Param value
footer:
  body: Footer value
  title: Footer Title
header: This is header

data:

param1: Awesome parameter

param2: Param value

footer:

body: Footer value

title: Footer Title

header: This is header

Now let’s include the process above in the Azure DevOps pipeline. I want to set the Param2 and FooterBody as variables and then pass them to the script. I will not go into detail about how to set the whole pipeline, but I’ll show you the important bits. To continue, save the script above in the code repository so you will be able to reference it from PowerShell task.

Step 1: Set the pipeline variables

Figure 1: Set variables for a pipeline in Azure DevOps

Step 2: Add PowerShell task to the pipeline

Figure 2: Add PowerShell task to the pipeline in Azure DevOps

Step 3: Set PowerShell script task

Now click on the PowerShell task and set it up.

Set Type to File Path.
Set Script Path to the script in your code repository.
In the Arguments field type -Param2 $(Param2) -FooterBody $(FooterBody) which will inject the pipeline variables to the script.
Depending on where your YML files are in the code repository structure, you also need to specify the context or Working directory for the script.

And that’s it.

I know, I know, the script can be more general and dynamic. For example, we could specify a YML file full path as the argument for the script, but for the sake of this demonstration that is fine. Leave your comments down below :).

TA-DA!

About Miha

Leave a Reply Cancel Reply