= Notes about the redo-c implementation of redo

* Without arguments, `redo` behaves like `redo all`.

* `.do` files always are executed in their directory, arguments are
  relative paths.

* Standard output of `.do` files is only captured as build product if
  `redo -s` is used, or the environment variable `REDO_STDOUT` is set to 1.
  Else, standard output is simply displayed.

* Non-executable `.do` files are run with `/bin/sh -e`.
  `redo -x` can be utilized to use `/bin/sh -e -x` instead, for
  debugging `.do` files or verbose builds.

* Executable `.do` files are simply executed, and should have a shebang line.

* When a target makes no output, no target file is created.  The target
  is considered always out of date.

* `default.do` files are checked in all parent directories up to `/`.

* Parallel builds can be started with `redo -j N`, this uses a job
  broker similar to but not compatible with GNU make.

* To detect whether a file has changed, we first compare `ctime` and
  in case it differs, a SHA2 hash of the contents.

* Dependencies are tracked in `.dep.BASENAME` files all over the tree.
  This is an implementation detail.

* Builds can be started from every directory and should yield same results.