--logfile

--logfile <file> routes the slicer's internal logging to a named file on disk. A file sink is added alongside any existing sinks rather than replacing them, so log messages continue to appear on the console (stderr) as well as in the file. There is no built-in option to suppress the console output; callers that need a clean machine-readable file must redirect stderr at the process level themselves.

The verbosity filter that determines which messages reach the file is the same global filter that --debug controls. The file sink inherits whatever verbosity level was already set when it is added. If --debug is omitted, the CLI defaults to level 2 (warning), and only warnings and above reach the file. To collect a useful trace for diagnosing a failed slice, pass --debug at level 4 (debug) or 5 (trace) alongside --logfile.

The flag passes the path string directly with no preprocessing: parent directories are not created, no extension is appended, and the file is opened as-is. If any component of the path is missing, the sink will fail to open and no file will be produced.