This PowerShell script deletes a specified Azure DevOps pipeline and its builds.

remove-pipeline-retention.ps1

param (
    [Parameter(Mandatory=$true)]
    [string]$PersonalToken,

    [Parameter(Mandatory=$true)]
    [string]$Organization,

    [Parameter(Mandatory=$true)]
    [string]$Project
)

function Invoke-AzureDevOpsAPI {
    param (
        [Parameter(Mandatory=$true)]
        [string]$Uri,

        [Parameter(Mandatory=$false)]
        [string]$Method = "Get",

        [Parameter(Mandatory=$false)]
        [string]$ContentType = "application/json",

        [Parameter(Mandatory=$false)]
        [string]$Body = $null
    )

    $token = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes(":$($PersonalToken)"))
    $header = @{authorization = "Basic $token"}

    Invoke-RestMethod -Uri $Uri -Method $Method -ContentType $ContentType -Headers $header -Body $Body
}

$pipelineName = Read-Host "Please enter the pipeline to delete"

# Get all build definitions
$url = "https://dev.azure.com/$Organization/$Project/_apis/build/definitions?api-version=6.0-preview.7"
$buildDefinitions = Invoke-AzureDevOpsAPI -Uri $url

$buildDefinitions.value | Sort-Object id | ForEach-Object {
    Write-Host $_.id $_.name $_.queueStatus

    if ($_.name -ne $pipelineName) {
        return
    }

    # Get all builds for a definition
    $url = "https://dev.azure.com/$Organization/$Project/_apis/build/builds?definitions=$($_.id)&api-version=6.0-preview.5"
    $builds = Invoke-AzureDevOpsAPI -Uri $url

    $builds.value | Where-Object { $_.retainedByRelease -eq "True" } | Sort-Object id | ForEach-Object {
        # Report on retain status
        Write-Host "BuildId:" $_.id "retainedByRelease:" $_.retainedByRelease

        # API call to update the build
        $url = "https://dev.azure.com/$Organization/$Project/_apis/build/builds/$($_.id)?api-version=6.0-preview.5"
        Invoke-AzureDevOpsAPI -Uri $url -Method Patch -Body (ConvertTo-Json @{"retainedByRelease"="false"}) -ContentType "application/json"
    }

    $url = "https://dev.azure.com/$Organization/$Project/_apis/build/definitions/$($_.id)?api-version=6.0-preview.1"
    Write-Host $url
    Invoke-AzureDevOpsAPI -Uri $url -Method Delete -ContentType "application/json"

    Write-Host "Pipeline: $pipelineName ($($_.id)) deleted"
}

Write-Host "Done"