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,
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}
                using -f operator inside the expression is a bit ambiguous, since you don't actually substitute any placeholders in the string. Why not just move $i++ outside the Rename-Item operation?
                    – Mathias R. Jessen
                Nov 16 '15 at 12:59
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
                I feel bad since I know it can be more verbose than this. So I will try to update it.
                    – Matt
                Nov 16 '15 at 13:17
        
Thanks for contributing an answer to Stack Overflow!
Please be sure to answer the question. Provide details and share your research!
But avoid …
Asking for help, clarification, or responding to other answers.
Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
                        
Related
                            
646How to run a PowerShell script
905How do you comment out code in PowerShell?
0Access a PowerShell Variable Immediately After Mutation
2Rename multiple files by adding an incrementing number prefix
2difficulty renaming batch of files with PowerShell without losing extension
2Batch copy and rename files with PowerShell
0Powershell- Rename. Insert Number in File name
2Rename-Item : add unique numeric sequence to prevent duplicate file names
0odd even file renaming powershell v.2
0Powershell Mass Rename files with a excel reference list
site design / logo © 2019 Stack Exchange Inc; user contributions licensed under cc by-sa 4.0
                            with attribution required.
                    rev 2019.10.7.35131