Save file in PowerShell script access denied - powershell

Question

I have a PowerShell script that is intended to modify a web config transform as a pre-build event in a build definition. I've gotten it working for the most part, however when it goes to save the updated file I am getting access denied.
Is there a way to give the right access, without opening a window as this is done via the TFS build agent?
Here is the script:
param(
[string]$buildTarget="Dev",
[string]$projectName="SalesTools"
)
$VerbosePreference = "continue"
Write-Verbose "Params: buildTarget = '$($buildTarget)', projectName = '$($projectName)'"
# Make sure path to source code directory is available
if (-not $Env:TF_BUILD_SOURCESDIRECTORY)
{
Write-Error ("TF_BUILD_SOURCESDIRECTORY environment variable is missing.")
exit 1
}
elseif (-not (Test-Path $Env:TF_BUILD_SOURCESDIRECTORY))
{
Write-Error "TF_BUILD_SOURCESDIRECTORY does not exist: $Env:TF_BUILD_SOURCESDIRECTORY"
exit 1
}
Write-Verbose "TF_BUILD_SOURCESDIRECTORY: $Env:TF_BUILD_SOURCESDIRECTORY"
$webConfig = "$($Env:TF_BUILD_SOURCESDIRECTORY)\$($buildTarget)\SalesTools.Web\$($projectName)\web.$($buildTarget).config"
#$webConfig = "$($Env:TF_BUILD_SOURCESDIRECTORY)\$($buildTarget)\SalesTools.Web\ARCTools\web.$($buildTarget).config"
Write-Verbose "File Path: $($webConfig)"
$doc = (gc $webConfig) -as [xml]
$versionNumber = $doc.SelectSingleNode('//appSettings/add[#key="versionNumber"]/#value').'#text'
Write-Verbose "Current Version Number: $($versionNumber)"
if (($versionNumber))
{
$versionInfo = $versionNumber.Split(".")
$versionIteration = $versionInfo[1]
$minorVersion = $versionInfo[2] -as [int]
$minorVersion = $minorVersion + 1
$currentIteration = Get-Iteration
$newVersionInfo = ("v: 1.$($currentIteration).$($minorVersion)")
}
else
{
Write-Error "Could not get version info from config."
exit 1
}
$doc.SelectSingleNode('//appSettings/add[#key="versionNumber"]/#value').'#text' = $newVersionInfo
$doc.Save($webConfig)

Answer 1

Before you read & update the web.config, try to change the "Read-Only" attribute of web.config file. Because by default, all the source files are "Read-Only".
Add this line before "$doc = ....":
attrib -R $webConfig /S