Reversing a file name based on delimiter then truncating part - powershell

Question

I need to rename many hundreds of files to follow a new naming convention, but I'm having awful trouble. This really needs to be scripted in powershell or VBS so we can automate the task in a regular basis.
Original File Name
Monday,England.txt
New File Name
EnglanMo
Convention Rules:
The file name is reversed around the delimiter (,) to England,Monday and then truncated to 6/2 char
Englan,Mo
The Delimiter is then removed
englanmo.txt
Say we had Wednesday,Spain.txt spain being 5 char, this is not subject to any reduction
SpainWe.txt
All the txt files can be accessed in one directory, or from a CSV, whatever is easiest.

Answer 1

Without having the exact details of your file paths, where it'll run, etc. you'll have to adapt this to point at the appropriate path(s).
$s= "Monday,England.txt";
#$s = "Wednesday,Spain.txt";
$nameparts = $s.split(".")[0].split(",");
if ($nameparts[1].length -gt 6) {
$newname = $nameparts[1].substring(0,6);
} else {
$newname = $nameparts[1];
}
if ($nameparts[0].length -gt 2) {
$newname += $nameparts[0].substring(0,2);
} else {
$newname += $nameparts[0];
}
$newname = $newname.toLower() + "."+ $s.split(".")[1];
$newname;
get-item $s |rename-item -NewName $newname;
I'm certain this isn't the most efficient/elegant way to do this, but it works with both of your test cases.

Answer 2

Use Get-ChildItem to grab the files, then on files that match your criteria, use regular expressions to capture the first two characters of the day of the week and the first six characters of the location, then use those captures to create a new filename. This is my best guess. Use -WhatIf on the Move-Item cmdlet until you get the regular expression and the destination path correct.
Get-ChildItem C:\Path\To\Files *.txt |
Where-Object { $_.BaseName -matches '^([^,]{2})[^,]*,(.{1,6})' } |
Move-Item -WhatIf -Destination {
$newFileName = '{0}{1}.txt' -f $matches[1],$matches[2]
Join-Path C:\Path\To\Files $newFileName.ToLower()
}

Answer 3

I think you should be able to achieve this by splitting the string into arrays in powershell and then recording the array to get your reverse.
For example:
$fileNameExtension = "Monday,England.txt";
$fileName = $fileNameExtension.split("."); // gets you an array [Monday,England][txt]
$fileparts = $fileName.split(","); // gets you an array [Monday][England]
//Create the new substring parts, notice you can now pull items from the array in any order you need,
//You will need to check the length before using substringing
$part1 = $fileparts[1].substring(0,5);
$part2 = $fileparts[0].substring(0,2);
//Now construct the new file name by rebuilding the string
$newfileName = $part1 + $part2 + “.” + $fileName[1];