When I did the post on creating temporary files http://msmvps.com/blogs/richardsiddaway/archive/2009/11/05/creating-temporary-files.aspx I said I’d modify it so the file would be created with a given extension.

It just involves adding another parameter $ext with a default empty string value.  If we give an extension

New-TempFile -size 2kb -ext "txt" -path "c:\test\test2"

Then we test to see if it starts with a .   and remove it.  We then replace the extension of the randomly generated filename using a regular expression match on the extension [ the regex is translated as 3 characters following a .  The \ is an escape character so . is read literally rather than as a wildcard]

Everything else is the same.  One other thing I might do is change the way data is put into the files.  For larger files its slow so I might do something different there.  This is one of great features of working with PowerShell like this – I can get a working script quickly and then refine it over time as I get chance to think about it.  Because I can work interactively at the prompt I can quickly test ideas before changing the script.