Using Powershells Trimstart to remove array of characters from filename - powershell

Question

I'm trying to do a simple bulk file rename to remove non-standard characters (e.g. " 0123456789-_.") from the start of a filename and just add a string to the filename.
e.g. '12 -_myfilename.doc' would become '012345 - myfilename.doc'
...where 012345 is my study number. I've tried using the script below but keep on getting the following error when stepping through the script executing the trimstart line...
"'Name' is a ReadOnly" property"
I guess that this is not a trimstart problem but the way in which I'm attempting to gather the result from it.
Any help appreciated.
The relevant part of the code looks like...
$MyFileObject=0
if ($MyRecursiveFlag) {
Get-ChildItem $MyStudyPath -recurse | where {$_.extension -in ".xls",”.xlsx”,".xslt",".pdf",".doc",".docx",".xlsm",".xml",".htm",".ppt"}|
ForEach-Object{
#Check if start of the file is compliant
$mymatch = [Regex]::Match($_, '\d{5}\s-\s')
if ($mymatch.Success){
#Already renamed correctly so nothing else to do
Write-Host "Okay - no changes $($_.Name)" -ForegroundColor Green
} else {
#No, it's not compliant so let's remove any preceding numbers, spaces and dashes etc
$MyFileObject = $_
$MyFileObject.Name = $MyFileObject.Name.trimstart(" 0123456789-_.")
#...and rename the file
Rename-Item -LiteralPath $MyFileObject.FullName -NewName "$($MyStudyNumber + ' - ' + $MyFileObject.Name)"
Write-Host "Renamed to $($MyFileObject.Name)" -ForegroundColor Yellow
}
}
}
I'm have the same problem when using Windows 7 PowerShell v3 and 5.1

Answer 1

You cannot change the Name of the current Get-ChildItem object (in your case $MyFileObject).
This should work (part of your script):
$MyFileObject = $_
$FileName = $MyFileObject.Name.trimstart(" 0123456789-_.")
#...and rename the file
Rename-Item -LiteralPath $MyFileObject.FullName -NewName "$($MyStudyNumber + ' - ' + $FileName)"
Write-Host "Renamed to $FileName" -ForegroundColor Yellow