PowerShell Backslash Bug Let Seven Rogue Processes Survive a Launch Cleanup

During a software launch on a Windows machine, a pre-launch cleanup script designed to stop stray project processes silently failed to terminate seven of them. The fault traced to a PowerShell wildcard pattern using double backslashes — a habit carried over from other languages — which never matched any real process command lines that use single backslashes. Because the pipeline produced no output whether it found zero matches or a genuinely clean system, the failure was indistinguishable from success. The issue was only caught at a final launch gate when a direct check of the process table revealed seven survivors, one already occupying a required port. The fix replaced the faulty wildcard pattern with a simple .NET string Contains() call, and the broader lesson adopted was that any filter which cannot fail loudly must be verified with a planted known-positive before its results can be trusted.