How to reorder date format in filename - date

Question

I've been looking all over stackoverflow and other forums online for any help with PowerShell variables and the rename function. I've had no luck.
The filename convention I use is: CompanyName 12.31.15 FS
(The "FS" describes the content of the file, in this case financial statements). Single digit months are preceded by 3 spaces so that the "FS" always ends up in the same column visually in windows explorer.)
The date format is m.dd.yy though I would like to change it to yy.mm.dd. The problem is I have over 30 folders with myriad of files in them- Some don't follow this file naming convention but if they use the m.dd.yy format, then the filename certainly does follow the convention.
So here's what I'm looking for:
A way to switch around only the date part of the file name from m.dd.yy to yy.mm.dd
In so doing, to also remove 2 of the leading spaces (where there are currently 3) and only have one space between CompanyName, date, and content.
The files must be changed in several directories within the "companies" folder
Examples:
Currently:
CocaCola 12.31.15 FS
CocaCola 6.30.15 FS
I want:
CocaCola 15.12.31 FS
CocaCola 15.06.31 FS

Answer 1

Retrieve the files using the Get-ChildItem cmdlet. Rename it using Rename-Item.
To switch the date you could parse it and format it to your desired output. However you could also do everything using a regex:
$yourCompanyPath = 'C:\tmp'
$callback = {
param($match)
'{0} {1}.{2:D2}.{3} {4}' -f $match.Groups["CompanyName"].Value,
$match.Groups["Year"].Value,
[int]$match.Groups["Month"].Value,
$match.Groups["Day"].Value,
$match.Groups["FS"].Value
}
$rex = [regex]'(?<CompanyName>\S+)\s+(?<Month>\d+)\.(?<Day>\d+)\.(?<Year>\d+)\s+(?<FS>FS)'
Get-ChildItem $yourCompanyPath | Foreach {
$_ | Rename-Item -NewName ('{0}{1}' -f $rex.Replace($_.BaseName, $callback), $_.Extension)
}
Source example:
CocaCola 6.30.15 FS.csv
CocaCola 12.31.15 FS.csv
Output:
CocaCola 15.06.30 FS.csv
CocaCola 15.12.31 FS.csv