gnuchess − Chess


gnuchess [ [[-|+]a] [-A aging-rate] [-b bookfile] [-B binbookfile] [-C cache-table-size] [-c] [[-|+]D ] [[-|+]E ] [[-|+]e ] [[-|+]F ] [-H hash-depth] [[-|+]h ] [-L language] [-l listfile] [[-|+]N] [[-|+]p ] [-P plys] [-r length] [-s savefile] [-S binbooksize] [-t] [-c hashfile-size] [-T transition-table-size] [[-|+]V] [-v] [-x] [-z search-fuzz] arg1 arg2 ]


Gnuchess plays a game of chess against the user or it plays against itself.

Gnuchess is an updated version of the GNU chess playing program. It has a simple alpha-numeric board display, an IBM PC compatible interface, or it can be compiled for use with the chesstool program on a SUN workstation or with the xboard program under X-windows. To invoke the program type:

- simple curses based version


- fancy version using curses and inverse video on UNIX, or IBM PC cursor controls and characters on MSDOS


- ASCII based version


- chesstool compatible version


- xboard compatible version


If one argument is given, it is the search time per move in [minutes:]seconds. So gnuchess 30 will generate one move every 30 seconds, while gnuchess 5:00 will generate one move every 5 minutes.

If two or more arguments are given, they will be used to set tournament time controls with the first argument of each pair being the number of moves and the second being the total clock time in minutes[:seconds]. Thus, entering gnuchess 60 5 will set the clocks for 5 minutes (300 seconds) for the first 60 moves, and gnuchess 30 3:30 will allow 3 minutes and 30 seconds for 30 moves.

gnuchess 30 5 1 :30 will allow 5 minutes for the first 30 moves and 30 seconds for each move after that. Up to 4 pairs of controls may be specified.

If no argument is given the program will prompt the user for level of play.

For use with chesstool or xboard, see the documentation on those programs.


At startup Gnuchess reads the binbook file if it is present. It then looks for a book file. If it is present it adds its contents to the binbook data. If the binbook file is writable a new combined binbook file is written.

The book consists of a sequence of openings. An opening begins with a line starting with a ! , the rest of the line is comments. Following this is a series of moves in algebraic notation alternating white and black separated by white space. A move may have a ? after it indicating this move should never be made in this position. Moves are stored as position:move so transpositions between openings can take place.


The hashfile if created should be on the order of 4 megabytes or gnuchess -c 22. This file contains positions and moves learned from previous games. If a hashfile is used the computer makes use of the experience it gained in past games. Tests run so far show that it plays no worse with the hashfile than without, but it is not clear yet whether it provides a real advantage.


Note: Piece letters and legal castling notation is determined by the language file. What is specified here is the default English.

Once gnuchess is invoked, the program will display the board and prompt the user for a move. To enter a move, use the notation e2e4 where the first letter-number pair indicates the origination square and the second letter-number pair indicates the destination square. An alternative is to use the notation nf3 where the first letter indicates the piece type (p,n,b,r,q,k). To castle, type the origin and destination squares of the king just as you would do for a regular move, or type o-o or 0-0 for kingside castling and o-o-o or 0-0-0 for queenside. To promote a pawn append the type of the new piece to the move, as in e7e8q or c7c8r.


-L lang

Use language lang from the file gnuchess.lang. If -L is not specified it defaults to the language used in the first line in the file. gnuchessr -L ger will use the german language.

-A aging-rate

Specify aging rate for hash table entries


Do [do not] search on opponents time.

-b bookfile

Use bookfile for opening book.

-B binbookfile

Use binbookfile for binary opening book.

-C cache-size

Specify evaluation cache table size (in entries).


Toggle DEEPNULL at runtime.


Toggle flag.threat.


Toggle flag.neweval to force evaluations instead of estimates


Toggle flag.noscore

-H hash-depth

pecify depth in plys for hashing.

-S size

Size of binbookfile for memory based and GDX books. For creating a binbookfile.

-P plylevels

Number of plys to include in the binbookfile. For generating a binbookfile.


Toggle flag.pvs

-c size

Create a new HASHFILE. File size is 2^size entries of approximately 65 bytes.


Do [do not] use hashfile.

-l pathname

Pathname of the loadfile use with the get or xget.

-r length

Rehash length times in searching entries for position in transposition table.

-s pathname

Pathname of the save file to use with the save command.


Show statistics for HASHFILE

-T size

Set the transposition table size to size entries. (minimum is MINTTABLE)


Show version and patchlevel.

-x value

Use value as the evaluation window xwndw.


In addition to legal moves, the following commands are available as responses. Note: command names are determined by the language file and may vary with the implementation. This is default English.

alg -- allow algebraic input (not implemented)

Awindow -- change Alpha window (default score + 90)

Bwindow -- change Beta window (default score - 90)

beep -- causes the program to beep after each move.

bd -- updates the current board position on the display.

bk -- Print out all moves for this position from the book as: move response value

book -- turns off use of the opening library.

both -- causes the computer to play both sides of a chess game.

black -- causes the computer to take the black pieces. If the computer is to move first the go command must be given.

eco -- Print out opening information for this game - lists ECO # and variations

coords -- show coordinates on the display (visual only)

contempt -- allows the value of contempt to be modified.

debug -- asks for a piece as color piece, as wb or bn, and shows its calculated value on each square.

debuglevel -- sets level of debugging output if compiled with debug options.

depth -- allows the user to change the search depth of the program. The maximum depth is 29 ply. Normally the depth is set to 29 and the computer terminates its search based on elapsed time rather than depth. If depth is set to (say) 4 ply, the program will search until all moves have been examined to a depth of 4 ply (with extensions up to 11 additional ply for sequences of checks and captures). If you set a maximum time per move and also use the depth command, the search will stop at the specified time or the specified depth, whichever comes first.

easy -- toggles easy mode (thinking on opponents time) on and off. The default is easy mode ON. If easy mode is disabled, the keyboard is polled for input every so often and when input is seen the search is terminated. It may also be terminated with a sigint.

edit -- allows the user to set up a board position.

# - command will clear the board.

c - toggle piece color.

. - command will exit setup mode.

pb3 - place a pawn on b3

Pieces are entered by typing a letter (p,n,b,r,q,k) for the piece followed by the coordinate.

The usual warning about the language file applies.

exit -- exits gnuchess.

first -- tells the computer to move first. Computer begins searching for a move. (same as "go").

force -- allows the user to enter moves for both sides. To get the program to play after a sequence of moves has been entered use the ’white’ or ’black’ command followed by ’go’.

gamein -- toggles game mode time control. Assumes the time specified for time control is the time for a complete game. Input with the level command should be the game time and the expected number of moves in a game.

get -- retrieves a game from disk. The program will prompt the user for a file name.

go -- tells the computer to move first. Computer begins searching for a move. (same as "first").

hash -- use/don’t use hashfile.

hard -- think on opponents time

hashdepth -- allows the user to change the minimum depth for using the hashfile and the number of moves from the begining of the game to use it.

help -- displays a short description of the commands and the current status of options.

hint -- causes the program to supply the user with its predicted move.

level -- allows the user to set time controls such as 60 moves in 5 minutes etc. In tournament mode, the program will vary the time it takes for each move depending on the situation. If easy mode is disabled (using the ’easy’ command), the program will often respond with its move immediately, saving time on its clock for use later on.

list -- writes the game moves and some statistics on search depth, nodes, and time to the file ’chess.lst’.

material -- toggle material flag - draws on no pawns and both sides < rook

Mwpawn, Mbpawn, Mwknight, Mbknight, Mwbishop, Mbbishop -- print out static position evaluation table

new -- starts a new game.

p -- evaluates the board and shows the point score for each piece. The total score for a position is the sum of these individual piece scores.

post -- causes the program to display the principle variation and the score during the search. A score of 100 is equivalent to a 1 pawn advantage for the computer.

unpost -- turn off the post display.

quit -- exits the game.

random -- causes the program to randomize its move selection slightly.

rcptr -- set recapture mode.

remove -- backout the last level for both sides. Equal to 2 undo’s.

reverse -- causes the board display to be reversed. That is, the white pieces will now appear at the top of the board.

rv -- reverse board display.

setup -- Compatibility with Unix chess and the nchesstool. Set up a board position. Eight lines of eight characters are used to setup the board. a8-h8 is the first line. Black pieces are represented by uppercase characters.

stars -- (gnuchessn only) add stars (*) to black pieces.

save -- saves a game to disk. The program will prompt the user for a file name.

switch -- causes the program to switch places with the opponent and begin searching.

test -- performs some speed tests for MoveList and CaptureList generation, and ScorePosition position scoring for the current board.

time otim -- time set computers time remaining, intended for synchronizing clocks among multiple players. -- otim set opponents time remaining, intended for synchronizing clocks among multiple players.

undo -- undoes the last move whether it was the computer’s or the human’s. You may also type "remove". This is equivalent to two "undo’s" (e.g. retract one move for each side).

white -- causes the computer to take the white pieces. If the computer is to move first the go command must be given.

xget -- read an xboard position file.

xwndw -- change X window. The window around alpha/beta used to determine whether the position should be scored or just estimated.





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