Some things that patches do:
- Add new features (items, monsters, traps, levels, artifacts) or change existing features.
- Add new playable roles, with their respective inventories, abilities, and quests. Examples: Convict, Pirate, Bard.
- Enhance the interface in some way, such as coloring elements of the text display to highlight certain items or alert you to low health or spell power.
- Biodiversity patch - adds new monsters (as well as features from some other patches)
- Convict patch - adds a new role, the Convict
- Grudge patch - causes certain classes of monsters (such as elves and orcs) to attack each other on sight
- Heck² patch - adds special predesigned rooms that can be generated in the maze levels of Gehennom
- Itlachiayaque - replaces the Orb of Detection with an artifact shield of reflection
- Lethe patch - adds a new branch, the Lethe Gorge, which appears before Gehennom
- Photography patch - adds photographs of monsters and dungeon features that are created whenever you apply an expensive camera
- Statuscolors - allows the user to configure the colors of the status line, to highlight ailments or indicate low health or power
- Underground rivers - occasionally generates rivers of water or lava across levels
Many Artifact YANIs have been made into patches.
Patch design is not only a popular activity for the NetHack community, but has also influenced the development of the game itself. The NetHack source includes some code that originated in patches for older versions. For example, many features of modern spellcasting first appeared in the Wizard Patch, which was written for NetHack 3.2.0 to 3.2.3 but proved so popular that it became a part of version 3.3.0.
Many variants of NetHack also use content from existing patches, in addition to creating new content. For example, SLASH'EM included Lethe water and torches, UnNetHack includes grudges and the Convict role, and Slash'EM Extended includes the Arch-lichen.
Adding patches to NetHack
If you want to know how to patch your NetHack sources, see the article on patching.
patch is also a program that can apply specially formed patch (also known as "diff" after the program that creates them) files. The usual invocation of patch is along the lines of
patch -p1 < patch_file
patch for the Windows platform may be downloaded from http://gnuwin32.sourceforge.net/ (though it seems to have problems under Vista and Win 7, fix: http://jameswynn.com/2010/03/gnu-patch-in-windows-7-or-vista/). After downloading, the patch.exe file needs to be placed in the system PATH, so that it can be found when it is invoked from the command line. One possible place would be in the same directory as the compiler used to compile NetHack (e.g. \mingw\bin) for the MinGW compiler).