How to delete files on the directory via MS SQL Server

declare @typeFile int = 0; -- for backup files or 1 for report files.
declare @folderPath varchar(max) = N'C:\temp'; --The folder to delete files.
declare @fileExtension varchar(100) = N'bak'; --File extension.
declare @cutOffDate datetime = DATEADD(hour , -12, getdate()); --The cut off date for what files need to be deleted.
declare @subFolder int = 0; --0 to ignore subFolders, 1 to delete files in subFolders.


EXECUTE master.dbo.xp_delete_file @typeFile, @folderPath, @fileExtension, @cutOffDate, @subFolder;

Credits: https://www.patrickkeisler.com/2012/11/how-to-use-xpdeletefile-to-purge-old.html

xp_cmdshell requires that a literal string be passed as parameter. You cannot construct a value on the fly.

Try this:

DECLARE @cmd NVARCHAR(MAX) = 
'xp_cmdshell ''del "C:\root\sfd_devtracker\' + @deletefile + '"''';
EXEC (@cmd)

Consider that xp_cmdshell must be enabled, for instance in this way.