pgn2fen

Extracts FEN of a specific move on a PGN game

Compile:

There's a Makefile just for that purpose, simply run:

make

Instalation:

Sorry, no install commands or scripts. Just have fun, if you like it, install it by hand :)

Running the program:

Running the program with no arguments, or with an invalid set of arguments will produce the following help:

Usage: ./pgn2fen input_game.pgn move [w/b] [output_position.fen]

input_game.pgn - A chess game in PGN format.

move - A move number.

w/b - OPTIONAL. Position reached after (w)hite or (b)lack move. Defaults to w.

output_position.fen - OPTIONAL. Output file. If not specified the output will be written to stdout.

For example, if game.png contains:

1. e4 c5 2. Nf3 d6

To print the position after white's second move:

./pgn2fen game.pgn 2

rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2

To print the position after black's second move:

./pgn2fen game.pgn 2 b

rnbqkbnr/pp2pppp/3p4/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R w KQkq - 0 3

Note: Since there's no way to get the initial position, i.e. before any player moves,

I'll provide it in case you need that:

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

About PGN

Portable Game Notation (PGN) is a plain text computer-processible format for recording chess games (both the moves and related data), supported by many chess programs.

PGN code begins with a set of "tag pairs" (a tag name and its value), followed by the "movetext" (chess moves with optional commentary). Moves are recorded using Standard Algebraic Notation.

About FEN

Forsyth–Edwards Notation (FEN) is a standard notation for describing a particular board position of a chess game. The purpose of FEN is to provide all the necessary information to restart a game from a particular position.

A FEN "record" defines a particular game position, all in one text line and using only the ASCII character set.

A FEN record contains six fields. The separator between fields is a space. The fields are:

1. Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending with rank 1; within each rank, the contents of each square are described from file "a" through file "h". Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken from the standard English names (pawn = "P", knight = "N", bishop = "B", rook = "R", queen = "Q" and king = "K"). White pieces are designated using upper-case letters ("PNBRQK") while black pieces use lowercase ("pnbrqk"). Empty squares are noted using digits 1 through 8 (the number of empty squares), and "/" separates ranks.

2. Active color. "w" means White moves next, "b" means Black.

3. Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle kingside), and/or "q" (Black can castle queenside).

4. En passant target square in algebraic notation. If there's no en passant target square, this is "-". If a pawn has just made a two-square move, this is the position "behind" the pawn. This is recorded regardless of whether there is a pawn in position to make an en passant capture.

5. Halfmove clock: This is the number of halfmoves since the last capture or pawn advance. This is used to determine if a draw can be claimed under the fifty-move rule.

6. Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.

Examples:

Here is the FEN for the starting position:

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

Here is the FEN after the move 1. e4:

rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1

And then after 1. ... c5:

rnbqkbnr/pp1ppppp/8/2p5/4P3/8/PPPP1PPP/RNBQKBNR w KQkq c6 0 2

And then after 2. Nf3:

rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2