Too many files to rename - powershell

Question

Renaming pdf-files with the command
get-childitem | % { rename-item $_ "2017-$_"}
renames correctly 33 files but applying the same command to more than 33 files produces filenames looking like 2017-2017-2017...-original.name.
How can I surmount that limitation for which I have not found any explication?

Answer 1

Since Rename-Item accepts piped input there is no need for a ForEach,
to exclude files beginning with 2017- :
Get-ChildItem *.pdf -exclude 2017-*.pdf |
Rename-Item -Newname { $_.Name -replace '^','2017-' } -whatif
to exclude any year/4digit-number prefix :
Get-ChildItem *.pdf |
Where-Object Name -notmatch '^\d{4}-' |
Rename-Item -Newname { $_.Name -replace '^','2017-' } -whatif
If the output looks OK, remove the -whatif

Answer 2

Looks like your code is chasing it's tail (i.e. it's renaming things that have already been renamed). Capture the list of files into a variable, then loop through that, renaming the captured list of files:
$filesToRename = Get-ChildItem -Filter '*.pdf'
$filesToRename | ForEach-Object {
Rename-Item -Path $_.FullName -NewName "2017-$($_.FullName)"
}
If you want to exclude already renamed files:
$prefix = '2017-'
$filesToRename = Get-ChildItem -Filter '*.pdf' | Where-Object { !$_.Name.StartsWith($prefix) }
$filesToRename | ForEach-Object {
Rename-Item -Path $_.FullName -NewName "$prefix$($_.FullName)"
}