Using Windows PowerShell to batch remove "[" character from filenames - powershell

Question

Trying to use PowerShell to remove an odd character, but it keeps breaking on [:
Filename is test [t].txt
Dir | Rename-Item -NewName { $_.Name -replace "[","_" }
Results in:
PS D:\test> Dir | Rename-Item -NewName { $_.Name -replace "[","_" }
Rename-Item : The input to the script block for parameter 'NewName' failed.
Invalid regular expression pattern: [.
At line:1 char:27
+ Dir | Rename-Item -NewName <<<< { $_.Name -replace "[","_" }
+ CategoryInfo : InvalidArgument: (test [t].txt:PSObject) [Rename-Item], ParameterBindingException
+ FullyQualifiedErrorId : ScriptBlockArgumentInvocationFailed,Microsoft.PowerShell.Commands.RenameItemCommand
I've tried a few common ways to escape the character \[, '[', ... and nada.
Thoughts and ideas?
PS: Trying the Replace() method with \[ escape:
PS D:\test> Dir | Rename-Item -NewName{ $_.Name.Replace("\[","_")}
Rename-Item : Cannot rename because item at 'Microsoft.PowerShell.Core\
FileSystem::D:\test\test [t].txt' does not exist.
At line:1 char:18
+ Dir | Rename-Item <<<< -NewName{ $_.Name.Replace("\[","_")}
+ CategoryInfo : InvalidOperation: (:) [Rename-Item], PSInvalidOperationException
+ FullyQualifiedErrorId : InvalidOperation,Microsoft.PowerShell.Commands.RenameItemCommand
PPS: The file DOES exist:
PS D:\test> dir
Directory: D:\test
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a--- 1/27/2018 4:08 PM 448 rb.bat
-a--- 1/27/2018 3:04 PM 4 test [t].txt
The appending of the PS header to the path by something inside PS when it sees a [ in the file name is the problem. If I replace the [ (bracket) with a ( (paren) everything works as expected.

Answer 1

The escape charachter is a backslash. So your regex pattern should look like this:
Get-ChildItem |
Rename-Item -NewName {$_.Name -replace '\[|\]','_'}
This will replace the opening square bracket and the closing square bracket.

Answer 2

Yes, I see that you resolved your situation with brute force. This code appears to produce the filename you desire.
PS C:\src\t\renfunc> Get-ChildItem
Directory: C:\src\t\renfunc
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a---- 2018-09-11 08:51 7 test [2].txt
PS C:\src\t\renfunc> Get-ChildItem | ForEach-Object { $_.Name -replace '\[|\]','_' }
test _2_.txt