Renaming script in PowerShell

There are a few things I would change in your code. For one thing, you call dir (Get-ChildItem) for every change of the file names when you could do that in one call.

Also, it lacks any form of checking to see if what the user has entered can actually be done for each file the Get-ChildItem returns.

The Get-ChildItem without a path specified will search items in the current location. If that is not what you want, maybe it is safer to set the path like in the code below.

$folder = '<ENTER THE PATH TO THE FOLDER WHERE THE FILES TO RENAME ARE HERE>'

# Prompt User how many characters in the front they want removed --> number
[int]$FrontRemove = Read-Host 'Enter how many characters you want removed from the front'

# Prompt user how many characters in the back they want removed --> number
[int]$BackRemove = Read-Host 'Enter how many characters you want removed from the back'

# Prompt user for string to be removed --> string
[string]$MiddleRemove = Read-Host 'Enter a string you want removed from the file name'

# Since we are using the -replace function, which is using Regular Expression replacement,
# we need to make sure all 'special' characters in the string are escaped.
if (![string]::IsNullOrEmpty($MiddleRemove)) {
    $MiddleRemove = [Regex]::Escape($MiddleRemove)
}

Get-ChildItem -Path $folder -File | Where-Object {$_.Name -notlike '*.ps1'} |
    ForEach-Object {
        $directory = $_.DirectoryName     # or [System.IO.Path]::GetDirectoryName($_.FullName)  or use Split-Path $_.FullName -Parent
        $filename  = $_.BaseName          # or [System.IO.Path]::GetFileNameWithoutExtension($_.Name)
        $extension = $_.Extension         # or [System.IO.Path]::GetExtension($_.Name)

        # test user input and remove/replace only if possible
        if ($FrontRemove -gt 0 -and $FrontRemove -lt $filename.Length) {
            $filename = $filename.Substring($FrontRemove)
        }
        if ($BackRemove -gt 0 -and $BackRemove -lt $filename.Length) {
            $filename = $filename.Substring(0, $filename.Length - $BackRemove)
        }
        if (![string]::IsNullOrEmpty($MiddleRemove)) {
            $filename = $filename -replace $MiddleRemove, ''
        }

        # now see if we still have a name left and if indeed the filename has changed
        if (![string]::IsNullOrEmpty($filename) -and $filename -ne $_.BaseName) {
            # re-append the extension of the file
            if (![string]::IsNullOrEmpty($extension)) { $filename += $extension }
            # join it with the directory to become a complete path and filename
            $newname = Join-Path -Path $directory -ChildPath $filename
            Rename-Item -LiteralPath $_.FullName -NewName $newname -Force
        }
        else {
            Write-Warning "The options you entered would remove the entire filename. Action skipped on '$($_.FullName)'"
        }
    }