Rules Files

Dependencies are encoded in a .rules file. A .rules file contains newline-separated blocks called rules. Each rule has three sections: targets, sources and command. Targets and sources are newline-separated lists of file paths. Command is a command-line invocation that presumably takes the sources as input and updates the targets. Each section ends with : alone on a line. For example, a .rules might contain this single rule:

build/game
:
src/game.h
src/game.cpp
:
c++
src/game.cpp
--std=c++17
-o build/game
:

That rule declares that the executable build/game depends on two source files src/game.h and src/game.cpp and builds by this line:

c++ src/game.cpp --std=c++17 -o build/game

Ruler uses unconventional syntax for the command. One invocation can span multiple lines without backslashes. To get a multi-line invocation, separate by ; alone on a line.

By using ruler’s build subcommand with the option --rules you can specify a path to a rules file like so:

ruler build --rules=game.rules

With no rules file specified, ruler will look in the current working directory for build.rules

Ruler build with the .rules file above will check whether game is up to do date. If it is not up to date, ruler looks for a way to recover it from a cache. If there is no way to recover the file from a cache, it runs the command.