From version 2.3 and up, a console has been included to make some things easier. 
Here is a list of currently added commands.


-disableconsole
   Disables the console for those who are unhappy with this feature. Add +enableconsole 1 to your command line to enable it again.

-flashfix
   Tells the game to use a different technique to flash the screen when taking damage. 
   You should only use this if the native flash does not work.

-forcepure
   This lets the server know you want to use strict crc checking. This setting is ignored by unsupported servers.
   Only use this setting if you know what you're doing. Disable it if you get disconnected for missing resources.

-framelimit <limit>
   Sets the framerate limit.

-fullscreenrender
   Tells the game to keep the renderer active when minimized in full screen mode. Prevents a crash with dgVoodoo and when loading a new map. 

-invertbypass
   Toggles whether the inverted vision should be used for Aliens and Predators. Added as a
   workaround for the black screen bug on some systems.

-legacymouse
   Toggles between the new (fixed) and old mouse input methods if you feel that the new method isn't for you.

-netstat
   Shows some network statistics including number of packets and data sent, bandwidth usage and dropped packets.

-setoutput  <parameters>
   Select which information should be outputted to the console.  Valid parameters:
   +: include - Includes to the output.
   -: exclude - Excludes from output.
   a: all - Includes all except for logging which must be separately enabled.
   c: console - Includes console messages.
   e: error - Includes errors.
   g: general - Includes general (yellow) messages.
   k: kill - Includes kills.
   m: message - Includes chat messages.
   o: origin - Includes the origin of console entries.
   p: player - Includes player joins/leaves.
   s: system - Includes system messages.
   l: log - Enables the logging to console.txt.

   The string must be a continuous string of the parameters above, without any other characters or spaces. Example:
   +lkm sets the output to log, kill, message.
   +a-gkmp sets the output to console, error, origin, player, system.
   +a -ps throws an error.

   Output defaults to console, error.

-showfps
   Toggles framerate display.

-splashbypass
   This setting disables the title screen since it's no longer needed in 2016.