Rename a list of files - powershell

Question

I need to rename all files below pwd named all_v4_0.csv to all_v4_1.csv.
So far, I have worked my way to this piece of PowerShell:
$oldfiles = dir -recurse | ?{$_.Name -eq "all_v4_0.csv"}
foreach ($o in $oldfiles) {
$o.CopyTo Join-Path $o.Directory.ToString() "all_v4_1.csv"
}
But the foreach loop fails with the message that
At line:2 char:15
+ $o.CopyTo Join-Path $o.Directory.ToString() "all_v4_1.csv"
+ ~~~~~~~~~
Unexpected token 'Join-Path' in expression or statement.
+ CategoryInfo : ParserError: (:) [], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : UnexpectedToken
What am I doing wrong here?
Update, 20150604
As commented below by Manuel Batsching, the original version can be fixed by adding two layers of parentheses: one to indicate function argument, and one to force evaluation order:
$oldfiles = dir -recurse | ?{$_.Name -eq "all_v4_0.csv"}
foreach ($o in $oldfiles) {
$o.CopyTo((Join-Path $o.Directory.ToString() "all_v4_1.csv"))
}
For the problem at hand, one of the solutions with .FullName.Replace would probably be easier.

Answer 1

PSH's parser is not reading the Join-Path and its arguments as an expression to evaluate and pass result to outer expression. So parentheses to force evaluation order.
But additionally CopyTo is a .NET member, rather than a PSH cmdlet, so it needs to have parentheses around its argument (and no space).
Thus:
$o.CopyTo((Join-Path $o.Directory.ToString() "all_v4_1.csv"))
(Possibly using PSH's Copy-Item cmdlet would be a cleaner option.)

Answer 2

Set the target name separately before doing the copy. The below should work:
$oldfiles = dir -recurse | ?{$_.Name -eq "all_v4_0.csv"}
foreach ($o in $oldfiles) {
$newName = $o.FullName.replace("all_v4_0.csv","all_v4_1.csv")
Copy-Item $o.FullName $newName
}

Answer 3

If you want to keep things simple you can also use string concatenation to create the target path.
Get-ChildItem -Recurse -Include 'all_v4_0.csv' |
ForEach { $_.MoveTo($_.Directory.FullName + '\all_v4_1.csv') }

Answer 4

Simply replace the substring in the new name of the files:
Get-ChildItem -Recurse -Include 'all_v4_0.csv' |
Rename-Item -NewName { $_.Name.Replace('4_0', '4_1') }