Group files whose names have embedded version numbers and process all but the latest versions

Preface:

• This is a self-answered question, which is why there's no solution attempt in the question itself.

• The task description is a focused reformulation of this now-deleted question.

I have a large set of files whose names contain version numbers; e.g.:

FileBam-0.10.1.zip
FileBam-0.2.0.zip
FileBoozle-1.7.2.zip
FileBoozle-1.7.5.zip
FileBoozle-1.7.10.zip
FileWam-0.97.40.zip
OtherFile-5.5.zip

Using PowerShell, I'd like to:

• group the files by shared named prefix, e.g. FileBam
• weed out groups that have only 1 element
• in each remaining, 2+-element group, delete all files except the one with the most recent version.

Use the following:

Get-ChildItem -Filter *.zip | 
  Group-Object -Property { ($_.BaseName -split '-')[0] } |
  Where-Object Count -gt 1 |
  ForEach-Object {
    $_.Group | 
      Sort-Object -Descending -Property { [version] ($_.BaseName -split '-')[-1] } |
      Select-Object -Skip 1
  } |
  Remove-Item -WhatIf

^{Note: The -WhatIf common parameter in the command above previews the operation. Remove -WhatIf and re-execute once you're sure the operation will do what you want.}

• Get-ChildItem is used to retrieve the list of input files, targeting files with filename extension .zip in the current directory (use -LiteralPath to target a different directory):

  • Matching files are represented as ([System.IO.FileInfo] instances and are sent through the pipeline (|) one by one.

• Group-Object is used to group the input files by the first --separated token in their base name:

  • The script block ({ ... }) acts as the implied Expression entry of a calculated property and specifies the grouping criterion.

  • In it, the automatic $_ variable refers to the input file-info at hand.

  • The .BaseName property contains the base file name (the file name without the extension) and its value is split into an array of tokens by -, via the -split operator, followed by extraction of the 1st token ([0]).

• Where-Object is used to filter the groups by whether they contain more than 1 (2 or more) elements (files), by way of testing whether the Count property value of the [Microsoft.PowerShell.Commands.GroupInfo] instances output by Group-Object, using the -gt (greater-than) operator and simplified syntax.

• ForEach-Object is used to process each 2+-element group:

  • Again, the automatic $_ variable refers to the input object at hand, which is a [Microsoft.PowerShell.Commands.GroupInfo] in this case, whose .Group property contains the group's array of elements. Sending that array to the pipeline (|) auto-enumerates the elements, i.e. sends them one by one.

  • Similar to the Group-Object call above, a script block acting as a calculated property is used as the sort criterion passed to Sort-Object, along with requesting descending sort order (-Descending), i.e. from highest to lowest version:

    • This time, it is the last ([-1]) token that is split off from the file base name, i.e. the version number string.

    • Said string is cast to type [version] ([System.Version]), resulting in an object that properly performs component-by-component comparisons when being sorted.

    • Select-Object is then used to skip the 1st result object (-Skip 1), which is the file with the highest version number in the group.

• The remaining objects sent through the pipeline are therefore the files to delete, and their deletion is performed via Remove-Item

  • As noted, the -WhatIf common parameter in the command previews the operation, i.e. tells you which files would be deleted, giving you the option to double-check whether the logic works as intended. Removing -WhatIf will perform actual deletion.