How to escape poison character in this mixed cmd / powershell code?

Question

I asked for a first explanation "here" and "here" but going to try a more complex situation I was unable (after two hours of trying) to understand how to solve. I read how the regular expression works but nothing, I went into the ball.

The modified code is this:

(Fsutil Dirty Query %SystemDrive%>Nul)||(powershell.exe -c "[Environment]::CommandLine; Start -Verb RunAs cmd /k, ("^""%~f0"^"" -replace '[;,()= &^]', '^$&')" & echo exit)

and the folder with the poison characters is this:

C:\Users\fposc\Desktop\Pie & tea % @ ' $^

I have tried to escape the ^ in the regular expression with \^ but don't work. I have escaped also ( and ) with $ and $. But nothing work:

(Fsutil Dirty Query %SystemDrive%>Nul)||(powershell.exe -c "[Environment]::CommandLine; Start -Verb RunAs cmd /c, ("^""%~f0"^"" -replace '[;,\(\)= &\^]', '^$&')" & exit)

I added the round brackets because I wanted to put all possible characters to make the code as generic as possible.

I don't know if I was right to open another question. Maybe I should change the original question? Since other combinations are possible and not having understood the mechanism I could open many other similar questions. What do you advise me to do?

My recommendation is to dispense with cmd.exe and just write the entire script in PowerShell. (IMO things will be more consistent, easier to understand, and less frustrating.) — Bill_Stewart, Oct 07 '21 at 20:20
Asuming that your match is a group, and not a literal string, there are several reserved characters which should be escaped. I'd have to assume similarly with your replace string too. This seems to me to be clearly a case that you have not researched the `-replace` operator or RegEx. In my opinion you should do that and make a resonable attempt at both ensuring that your replace command is correct, before attempting to correctly escape it. — Compo, Oct 07 '21 at 20:51

mklement0 · Accepted Answer · 2021-10-07T22:05:58.650

The problem is the presence of $ in your folder name, which causes the PowerShell command to interpret it as the start of a variable reference.

The workaround is to use an aux. environment variable to store the batch file's full path and let PowerShell perform its escaping based on this variable's value:

:: Unless already elevated, re-invoke this batch file with elevation,
:: via PowerShell.
set "__THISFILE=%~f0"
Fsutil Dirty Query %SystemDrive% >Nul || (powershell.exe -c "Start-Process -Verb RunAs cmd /k, ($env:__THISFILE -replace '[ &%%^]', '^$&')" & exit)

I have updated the answer to your original question to incorporate this approach, which now shows a - hopefully - robust approach to on-demand re-invocation of a batch file with elevation, including support for arguments.

How to escape poison character in this mixed cmd / powershell code?

1 Answers1