"(" char doesn't work in PowerShell - powershell

Question

I can't get this to work. It doesn't like the "(" char;
how do I fix it?
Dir | Rename-Item -NewName { $_.name -replace "(","" }
How do I handle this type of special character in PowerShell?

Answer 1

You've got a great explanation of the exact cause of your problem from #vonPryze, but there's a much simpler solution. The -replace operator uses regular expressions which need escaping, but the .Replace() string method just uses strings. So if you don't need a regex, just use the method and there's no need to escape anything:
dir | rename-item -NewName { $_.name.Replace("(","") }

Answer 2

Let's try analyzing the problem a bit. First off, create some dummy files that contain a parenthesis like so,
for($i=0;$i -le 4; ++$i) { set-content -path $("file($i).txt" -f $i) -value $i }
Output:
gci
Directory: C:\temp\foo
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a--- 17.2.2014 10:34 3 file(0).txt
-a--- 17.2.2014 10:34 3 file(1).txt
-a--- 17.2.2014 10:34 3 file(2).txt
-a--- 17.2.2014 10:34 3 file(3).txt
-a--- 17.2.2014 10:34 3 file(4).txt
Now that we have some test data, let's try to run the command that provied an error message like so,
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: (file(0).txt:PSObject) [Rename-Item], ParameterBind ingException
+ FullyQualifiedErrorId : ScriptBlockArgumentInvocationFailed,Microsoft.PowerShell.Commands.Re nameItemCommand
Oops! The error message says that an invalid regular expression was used. That means -replace is not going to just replace strings but it supports regular expressions too!
In order to get -replace to treat the input as literal text instead of a regex, the input needs to be escaped. The simple way is to insert backslashes \, but this gets soon tedious. There luckily is an easier way, as .Net Regex class has a built-in escape method [Regex]::Excape(). Like so,
Dir | Rename-Item -NewName { $_.name -replace [regex]::escape("("),"" }
Output:
ls
Directory: C:\temp\foo
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a--- 17.2.2014 10:34 3 file0).txt
-a--- 17.2.2014 10:34 3 file1).txt
-a--- 17.2.2014 10:34 3 file2).txt
-a--- 17.2.2014 10:34 3 file3).txt
-a--- 17.2.2014 10:34 3 file4).txt

Answer 3

Dir | Rename-Item -NewName { $_.name -replace "\(","" } # This works