Renaming multiple files with different names - powershell

Question

I am a programmer by no means and am brand new to using powershell, but have been tasked with setting up some batch export processes for daily files we FTP. I need to come up with a script that will take changing file names and change them within the same directory to new names;
Example: files will come in as below (YYYYMMDD will be the changing variable)
YYYYMMDD_Share_Support.txt
YYYYMMDD_Person_Support.txt
We need them to be stripped from the above to:
Share.txt
Person.txt
so on and so forth.
I have found ways to make this work, but only on an as needed basis for one file at a time with specific names, not names that will change daily.
So far I am using:
Get-ChildItem -Filter *.txt
Dir | %{Rename-Item $_ -NewName ("NEWFILENAME.txt" -f $nr++)}

Answer 1

You could use the regex -replace operator inside a pipeline-bound scriptblock:
$files = Get-ChildItem -filter *.txt
$files |Rename-Item -NewName { $_.Name -replace '^\d{8}_(.*)_Support\.txt$', '$1.txt' }
As suggested by TheIncorrigible1, if you know the relative position of the word you need, you can also use -split:
$files |Rename-Item -NewName {'{0}.txt' -f ($_.Name -split '_')[-2]} # grab 2nd last word

Answer 2

How about:
dir *.txt |
rename-item -newname { $null,$base,$null = $_.basename -split '_'; "$base.txt" } -whatif

Answer 3

Probably a longer version of the answer. An alternative mentioned by #TheIncorrigible1
$logDir = "D:\Satish\TestFolders"
cd $logDir
$files = ls
foreach ($file in $files){
$fileSplit=($file.ToString()).split("_")
ren $file "$($fileSplit[1]).txt"
}
And for Share.txt to YYYYMMDD_Share_Support.txt
$logDir = "D:\Satish\TestFolders"
cd $logDir
$files = ls
$date = Get-Date -Format "yyyyMMdd"
foreach ($file in $files){
$fileSplit=($file.ToString()).split(".")
ren $file "$($date)_$($fileSplit[0])_Support.txt"
}