Rename first 20 characters of every filename in a file - powershell

Question

I am trying to write a script in powershell to remove the first 20 characters of every MP3 filename in a folder, I have created a file 'test.ps' and inserted the powershell code below into it,
gci *.mp3 | rename-item -newname { [string]($_.name).substring(20) }
When I run this file in powershell.exe nothing happens,
Can anyone help? Thanks.

Answer 1

This may get you started. (There are probably much more concise ways, but this works and is readable when you need to maintain it later. :-) )
I created a folder C:\TempFiles, and created the following files in that folder:
TestFile1.txt
TestFile2.txt
TestFile3.txt
TestFile4.txt
(I created them the old-fashioned way, I'm afraid. <g>. I used
for /l %i in (1,1,4) do echo "Testing" > TestFile%i.txt
from an actual command prompt.)
I then opened PowerShell ISE from the start menu, and ran this script. It creates an array ($files), containing only the names of the files, and processes each of them:
cd \TempFiles
$files = gci -name *.txt
foreach ($file in $files) {
$thename = $file.substring(4);
rename-item -path c:\TempFiles\$file -newname $thename
}
This left the folder containing:
File1.Txt
File2.Txt
File3.Txt
File4.Txt
File5.Txt
In order to run a script from the command line, you need to change some default Windows security settings. You can find out about them by using PowerShell ISE's help file (from the menu) and searching for about_scripts or by executing help about_scripts from the ISE prompt. See the sub-section How To Run A Script in the help file (it's much easier to read).

Answer 2

Your code actually works. Two things...
Rename the file to test.ps1.
Run it in the folder you have your MP3 files in. Since you didn't provided a path to Get-ChildItem it will run in the current directory.
I tested your line by making a bunch of mp3 files like this -
1..30 | % { new-item -itemtype file -Name (
$_.ToString().PadLeft(30, 'A') + ".mp3" )}

Answer 3

I would use a more "safer" way (you'll get an error if the file name is shorter than the length in question, you are also targeting the file extension as a part of the total characters). Check if the base name of each file is greater than 21 characters (if you remove the first 20 it can be still have a name with one character long). It can fail if the directory contains a file with same name after you removed the first 20, you can develop it further on your own):
gci *.mp3 | foreach{
if($_.BaseName.Length -ge 21)
{
$ext = $_.Extension
$BaseName = $_.BaseName.Substring(20)
Rename-Item $_ -NewName "$BaseName$ext"
}
}

Answer 4

// delete (replace with empty char) first 20 charters in all filename witch is started with "dbo."
// powershell
Get-ChildItem C:\my_dir\dbo -Recurse -Force -Filter dbo.* | Where-Object {!$_.PSIsContainer} | Rename-Item -NewName { ($_.name).Substring(20) }