Powershell - modify Date and Time of a file to reflect its filename

Question

I have had to recover a load of files from a memory card to my hdd. The names for the recovered files on my hdd are in the format "yyyymmdd_hhmmss.mp4", and do show the correct times & dates.

However, the date modified column for these recovered files shows quite a different date (in the format "dd/mm/yyyy hh:mm" (obviously the seconds show when viewing their properties) as I reside in the UK), and I would like these date modified stamps to reflect their filenames once again. I have started to write a PowerShell script to extract the date & time to variables, and this is what I've done so far:

foreach ($file in Get-ChildItem *.mp4)
{
    $yy = $file.Name.substring(0,4)
    $mm = $file.Name.substring(4,2)
    $dd = $file.Name.substring(6,2)
    $hh = $file.Name.substring(9,2)
    $min = $file.Name.substring(11,2)
    $ss = $file.Name.substring(13,2)
}

However, my experience with PS cannot write the date modified attribute to reflect the filename. Please could someone help me?

Kind regards,

Rob Hughes.

Answer 1

To set the "date modified" property, update the $file.LastWriteTime property. You can use [datetime]::ParseExact() to parse the date and time from the files name in a single operation.

foreach($file in Get-ChildItem -Filter *.mp4)
{
    $file.LastWriteTime = [datetime]::ParseExact($file.BaseName, 'yyyyMMdd_HHmmss', $null)
}

Answer 2

The value you want to change to update the 'Date Modified' field is called .LastWriteTime. Here's how you'd change that with your current code.

    foreach ($file in Get-ChildItem *.mp4)
    {
    $yy = $file.Name.substring(0,4)
    $mm = $file.Name.substring(4,2)
    $dd = $file.Name.substring(6,2)
    $hh = $file.Name.substring(9,2)
    $min = $file.Name.substring(11,2)
    $ss = $file.Name.substring(13,2)

   #Create a Date Time object based on the file name
   $date =  get-date -Year $YY -Month $MM -Day $DD -Hour $hh -Minute $min -Second $SS

   #Echo out to screen
   Write-Host "Setting $($file.BaseName) dateModified as $($Date.Date)"
   $file.LastWriteTime = $Date
    }

Making a DateTime object is by far the easiest way to do this. Big props to you OP for sussing out the good bits from the file name like that, well done.