This will replace invalid characters in filename with a placeholder string. This will help to generate unique filenames.

Replace-InvalidFileNameChars.ps1

# based on https://stackoverflow.com/a/15121461
Function Replace-InvalidFileNameChars {
  param(
    [Parameter(Mandatory=$true,
      Position=0,
      ValueFromPipeline=$true,
      ValueFromPipelineByPropertyName=$true)]
    [String]$Name
  )

  $r = @{
    '"' = "-dq-";
    '<' = "-gt-";
    '>' = "-st-";
    '|' = "-pi-";
    '*' = "-as-";
    '\' = "-bs-";
    '/' = "-fs-";
    '?' = "-qm-";
    '.' = "-dt-";
    ' ' = "-sp-";
}

    $regexes = $r.keys | foreach {[System.Text.RegularExpressions.Regex]::Escape($_)}
    $regex = [regex]($regexes -join '|')

    $callback = { $r[$args[0].Value] }

    return $regex.Replace($Name, $callback)

}

Replace-InvalidFileNameChars "feature/abcdef"
Replace-InvalidFileNameChars "feature/abc|def"