Backup-File.ps1

<#
.Synopsis
   Create backup of file
.DESCRIPTION
   Create backup of a file
.EXAMPLE
   Backup-File.ps1 file.to.backup.txt
.EXAMPLE
   Backup-File.ps1 -File file.to.backup.txt
#>
[CmdletBinding()]
[Alias()]
Param
(
    # File to backup
    [Parameter(Mandatory=$true,
                ValueFromPipelineByPropertyName=$false,
                Position=0)]
    $File
)

Process
{
    $filename = $File
    $dateStr=Get-Date -format yyMMdd

    if(Test-Path -Path $filename){
        if(Test-Path -Path "$($filename).$($dateStr).bak"){
            Move-Item "$($filename).$($dateStr).bak" "$($filename).prev_$($dateStr).bak"
        }
        Copy-Item $filename "$($filename).$($dateStr).bak"
    }
}