PowerShell Substring “索引超出字符串长度”

Question

I have a List of Filenames which I have to split in a certain way. The easiest way I know is to use Substring on them.

The Filenames are formatted like; VLAN_[Random Name]_[Random Number].ini

So my guess was to use Substring to get the Filename from the 5th to the 4th last Postion

$FileList = Get-ChildItem -Path $FileDir | Where-Object -Property name -like "VLAN_*"

ForEach($File in $FileList){
    [String]$SheetName = $File.Name # Name Formatted like: VLAN_[Random Name]_[Random Number].ini
    $SheetName = $SheetName.Substring(5,$Sheetname.Length-4)
    Write-Host $File.Name
    Write-Host $SheetName
    Read-Host
}

When I tried with this it gave me back an "Index is not in String length" Error, but when I used a 4 or less as a Starting point for my Substring it worked. Does it have something to do with the "_" symbol? Also, when I start from 0 the last 4 chars get deleted like they should, but if the starting point isn't 0 it never deletes the last 4 chars.

Heres the Output I get with both Substring methods:

# Substring(5,$Sheetname.Length-4)

"Index is not in String length" Error

VLAN_BMA_201.ini
VLAN_BMA_201.ini

"Index is not in String length" Error

VLAN_CCTV_120.ini
VLAN_CCTV_120.ini

# Substring(4,$Sheetname.Length-4)

VLAN_BMA_201.ini
_BMA_201.ini

VLAN_CCTV_120.ini
_CCTV_120.ini

Answer 1

If your file names always have the same structure with the underlines in it you can make this task a lot easier with the split method like this:

ForEach($File in $FileList){
    ($File.BaseName -split '_' )[1..2] -join '_'
}

Answer 2

The second parameter in Substring() is the length of the substring, so when you say that is <LengthOfString>-4 and you are starting the substring at position 5, you will always be going beyond the length of the string. You need to add the first 5 characters you are skipping to what you subtract to the length of the substring. So try $SheetName = $SheetName.Substring(5,$Sheetname.Length-9) instead and you should get what you want.

Alternatively, use a simple regular expression:

if ($SheetName -match 'VLAN_(?<stuffIcareAbout>.+)\.ini')
{
    $SheetName = $Matches.stuffICareAbout
}