What is Ruler?
Ruler is a command-line build tool like Make or Ninja. It uses config files with the extension .rules A .rules file describes:
- The dependence relationship between files
- For each target file, a command to update
When invoked like this:
ruler build
… Ruler computes which files need to update (and in what order), and runs the commands for those files only.
Software developers use tools like this to manage complex C/C++ projects. Ruler can help manage any project with a dependence graph of files. Example:
Anatomy of a .rules file
A .rules file contains newline-separated blocks called rules. Each rule consists of three sections: targets, sources and command. Targets and sources are newline-separated lists of file paths. Command is a command-line invocation meant to update the targets using sources as input. Each section is terminated by a single “:” alone on a line. For example, a rule might look like this:
hello.exe
:
hello.cpp
:
c++
--std=c++17
hello.cpp
-o hello.exe
:
With the rule above, if hello.cpp is out of date, hello.exe rebuilds by this command:
c++ --std=c++17 hello.cpp -o hello.exe
A .rules file might consist of several rules, thereby encoding the whole dependence graph. A more in-depth discussion of the rules file syntax can be found here: