A brief overview of a CQL file

A CQL file consists of the word cql, followed by a parentheses enclosed list of arguments, followed by filters.

For example, here is a CQL file to find games where Black has at least two rooks and is stalemated

      cql (input heijden.pgn)
       btm
       stalemate
       r>= 2

CQL first reads the input file from the input parameter. Then CQL reads each game in the file heijden.pgn. Next, CQL plays through each position in each game. Each time CQL reads a position, CQL checks whether each of the so-called filters is true of that position.

In this case there are three filters: btm, stalemate, and r>= 2. btm will be true if the position is black to move; stalemate will be true if the position is stalemate; r>= 2 is true if there are at least two black rooks in the position.

If all these filters are true for a position, then CQL outputs the game (with some comments) to the output file.

Basic syntax

A CQL file is mostly a sequence of filters separated by whitespace and punctuation.

moving on

See CQL file: structure and operation for more detail.