Powershell: How do I shift a date (format: yyyymmdd) from any position in the file name to end of the file name?

Question

Currently im using

dir | Rename-Item -NewName {$_.name -replace "",""}

to rename files in a directory. The file names vary and need to be unified.

Examples for file names:

1. 20211112_CLAM_30001_Important information on xyz_DK
2. CLAM_DK_20201002_30001_Protocol for PA01 - email
3. DK_30001_Update on customer increase_signed_20220102

Unified format:

CLAM_30001_Arbitrary text_yyyymmdd

There is a date as an 8 digit no. at an arbitrary position in the file name. The date needs to be the very end of the file name. How can I move it to the end? (Perhaps REGEX?)

Answer 1

Try the following:

gci | Where { $_.Name -Match '\d{8}'} | ForEach {
        if ($_.Name -Match '^(\d{8})_(.+)$') { 
            Rename-Item $_ ( $_.Name -Replace  '^(\d{8})_(.+)$','$2_$1' ) }
        elseif ($_.Name -Match '^(.+_)(\d{8})_(.+)$') { 
            Rename-Item $_ ( $_.Name -Replace '^(.+_)(\d{8})_(.+)$', '$1$3_$2' ) }
    }

The code checks where the 8 digits are found in the filename (beginning or other) and rename the files accordingly. No need to check if the 8 digits are at the end.

Answer 2

You can do this without ForEach-Object using a scriptblock for parameter -NewName in which you simply move the captured 8 digits result from the Where-Object clause towards the end of the file's BaseName.
Then trim off any leading or trailing underscores and make sure there will be no doubled-up underscores in the new name. Finally append the file's extension (if any).

If a file already had the desired name format, it will not be renamed (a no-op)

Get-ChildItem -Path 'X:\ThePath' -File | Where-Object { $_.BaseName -match '(\d{8})' } | 
Rename-Item -NewName { (('{0}_{1}' -f ($_.BaseName -replace $matches[1] ), $matches[1]).Trim("_") -replace '_+', '_') + $_.Extension }