How to rename files with sequential even and odd numbers in PowerShell? - powershell

Question

I would like to know how I can rename the files from a specific folder with a sequence of only even and odds numbers in PowerShell. E.g. Folder1: pag_001.jpg, pag_003.jpg, pag_005.jpg.... pag_201.jpg , Folder2: pag_002.jpg, pag_004.jpg, pag_006.jpg.... pag_200.jpg. It is because I have a document that was scanned first the odds pages and secondly the even pages, therefore their file names are in a consecutive sequence from 1 to 201. Then I separated one half of the files which are the odds pages in a new place: Folder1, and the second half,the even pages in the Folder2. That is why I would like change the names first and the join again together with their new names.
I have tried this based in a similar post:
At the moment I could generate even number sequences like that:
ForEach ($number in 1..100 ) { $number * 2}
and odd numbers like that:
ForEach ($number in 0..100 ) { $number *2+1}
and wanted apply the sequences generated before to rename my files like that:
cd C:\test\Folder1
$i = $number * 2
Get-ChildItem *.jpg | %{Rename-Item $_ -NewName ('pag_{0:D3}.jpg' -f $i++)}
but it doesn't works! Any suggestions are welcome
Regards,

Answer 1

Your $i++ adds 1 each time, this is why it also add even numbers,
You can create array of Odd Numbers then use the $i++ to step one item in the array, like this:
$path = "C:\test\Folder1"
$oddNumbersArray = 0..100 | % {$_ *2 +1}
$i = 0
Get-ChildItem $path -Filter *.jpg | % {Rename-Item $_ -NewName ("pag_$($oddNumbersArray[$i]).jpg") ;$i++}
For Even Numbers change the $oddNumbersArray line to {$_ *2}

Answer 2

Bunch of ways to do this. For mine we add each index as a member so that it is more easily accessible in the rename item script block.
$index = 0
Get-ChildItem $path -Filter "*.jpg" | ForEach-Object{
$index = $index +2
$_ | Add-Member -Name "Index" -MemberType NoteProperty -Value $index -PassThru
} | Rename-Item -NewName {'pag_{0:D3}.jpg' -f $_.Index} -WhatIf
Using Add-Member in a ForEach-Object we update the value of index and then add it as a property of the same name. Then in your rename-item scriptblock we can call that property. Remove the -WhatIf after you verified the new names are what you wanted. Switch $index between 0 and -1 for even and odd respectively.
Another method using a global index variable and mitigating the pipeline by using calculated properties to create the pipeline variables that Rename-Item uses.
$path = "C:\Temp\csv"
$global:index = 0 # Use -1 for odd
Get-ChildItem $path -Filter "*.csv" |
Select-Object #{Name="Path";Expression={$_.FullName}},
#{Name="NewName";Expression={$global:index = $global:index + 2; 'pag_{0:D3}.jpg' -f $global:index}} |
Rename-Item -WhatIf