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System.IO.Path - ChangeExtension()

The method ChangeExtension() of the System.IO.Path class modifes a file name's extension.

The following PowerShell example useses ChangeExtension to rename all *.ps1 files in a directory to *.txt files:

foreach ($file in get-item *.ps1) {
   rename-item $file  ([System.IO.Path]::ChangeExtension($file, 'txt'))
}