-``-c`` or ``--command=COMMANDS`` evaluate the specified commands instead of reading from the commandline, passing any additional positional arguments via ``$argv``.
Note that, unlike other shells, the first argument is *not* the name of the program ``$0``, but simply the first normal argument.
-``-C`` or ``--init-command=COMMANDS`` evaluate the specified commands after reading the configuration, before running the command specified by ``-c`` or reading interactive input.
-``-d`` or ``--debug=DEBUG_CATEGORIES`` enable debug output and specify a pattern for matching debug categories. See :ref:`Debugging <debugging-fish>` below for details.
-``-o`` or ``--debug-output=DEBUG_FILE`` specify a file path to receive the debug output, including categories and :envvar:`fish_trace`. The default is stderr.
-``-p`` or ``--profile=PROFILE_FILE`` when :command:`fish` exits, output timing information on all executed commands to the specified file. This excludes time spent starting up and reading the configuration.
-``--profile-startup=PROFILE_FILE`` will write timing information for fish's startup to the specified file. This is useful to profile your configuration.
While fish provides extensive support for :ref:`debugging fish scripts <debugging>`, it is also possible to debug and instrument its internals.
Debugging can be enabled by passing the ``--debug`` option.
For example, the following command turns on debugging for background IO thread events, in addition to the default categories, i.e. *debug*, *error*, *warning*, and *warning-path*:
Available categories are listed by ``fish --print-debug-categories``. The ``--debug`` option accepts a comma-separated list of categories, and supports glob syntax.
The following command turns on debugging for *complete*, *history*, *history-file*, and *profile-history*, as well as the default categories:
Debug messages output to stderr by default. Note that if ``fish_trace`` is set, execution tracing also outputs to stderr by default. You can output to a file using the ``--debug-output`` option:
The categories enabled via ``--debug`` are *added* to the ones enabled by $FISH_DEBUG, so they can be disabled by prefixing them with ``-`` (``reader-*,-ast*`` enables reader debugging and disables ast debugging).