BackupAllSPSites

$backupLocation = "D:\SPBACKUP\SiteCols"
$logFile = join-path $backupLocation "log.txt"

cd $backupLocation

function Write-Log($message)
{
 $message
 $message = (get-date).ToString("yyyy/MM/dd HH:mm:ss") + " - " + $message
 $message >> $logFile
}

$source = @"
using System;

public class HistoryBackup
{
 public DateTime CreatedDate;
 public DayOfWeek WeekDay;
 public int DaysOld;
 public int WeeksOld;
 public string FullFileName;
 
 public HistoryBackup(string fileName)
 {
  FullFileName = fileName;
  int idx = System.Text.RegularExpressions.Regex.Match(fileName, @"_\d{12}\.").Index; //xxx_201107272300.bak 3 4, 12
  CreatedDate = DateTime.ParseExact(fileName.Substring(idx + 1, 8), "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);
  WeekDay = CreatedDate.DayOfWeek;
  DaysOld = (int) DateTime.Today.Subtract(CreatedDate).TotalDays;
  WeeksOld = GetWeekDiff(DateTime.Today, CreatedDate);
 }
 
 private int GetWeekDiff(DateTime today, DateTime adate)
 {
  int todayWeekNum = (int) today.DayOfWeek;
  DateTime firstDayofThisWeek = today.AddDays(todayWeekNum * -1);
  int x = (int) firstDayofThisWeek.Subtract(adate).TotalDays;
  if (x <= 0)
  {
   return 0;
  }
  if (x % 7 > 0)
  {  
   return (x / 7) + 1;
  }
  else
  {
   return x / 7;
  }
 }
 
 public bool Dispose()
 {
  if (WeeksOld == 1 && (WeekDay == DayOfWeek.Friday || WeekDay == DayOfWeek.Wednesday))
  {
   return false;
  }
  System.IO.File.Delete(FullFileName);
  return true;
 }
}
"@
    
Add-Type -TypeDefinition $source

function BackupSiteCollection($siteCol)
{
 $datePart = (get-date).tostring("yyyyMMddHHmm")
 $namePart = $siteCol.Url.ToLower().replace("https://", "").replace("http://", "").replace(":", "-").replace("/", "-").replace(".", "-")
 $fileName = $namePart + "_" + $datePart + ".bak"
 $fullName = join-path $backupLocation $fileName
 
 $url = $siteCol.Url
 
 Write-Log "Start to backup $url to $fullName"
 Backup-SPSite -identity $siteCol.Url -path $fullName -force
 Write-Log "Finish backup of $url"
 
 dir | ? { $_.Name -like "$namePart" + "_????????????.bak" -and $_.Name -ne $fileName} |
  % {
       $hisBackup = new-object HistoryBackup -ArgumentList $_.FullName
       $deleted = $hisBackup.Dispose()
       if ($deleted)
       {
        Write-Log "$_.Name is deleted."
       }
    }
}

$snapin = Get-PSSnapin | Where-Object {$_.Name -eq 'Microsoft.SharePoint.Powershell'}
if ($snapin -eq $null) {

    Write-Host "Loading SharePoint Powershell Snapin"
    Add-PSSnapin "Microsoft.SharePoint.Powershell"
}


get-spsite | % { BackupSiteCollection $_ }