Multiple files in get content and set content

Hi powershell,

Here is my sample script:
$s = Get-Content 'H:\aa.txt'
$s = $s -replace("\s+",",")
$s | Set-Content 'H:\aa.csv'

How to multiple files in get content and set content?
e.g
$s = Get-Content 'H:\aa.txt,H:\bb.txt'
$s = $s -replace("\s+",",")
$s | Set-Content 'H:\aa.csv,H:\bb.txt'

Any idea?

Thanks