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Recipes

Recipes describe how to build stuff, both individual software packages, complete root file systems as well as associated utilities such as SDKs. This chapter gives a short introduction to the conventions used as well as a short example.

When starting a build (oe bake), OE-lite starts by parsing all recipe files in all registered layers, pruning recipes which are not compatible with the current target architecture.

Naming conventions

Recipe files end with the suffix .oe, and should reside in subdirectories of the recipes directory in one of the registered OE-lite layers.

The filename must follow the format <name>_<version>.oe, for example tcpdump_4.6.2.oe, where <name> is the name of the item described and <version> is the version of the software. The name part must not contain an underscore, since everything after the first underscore is taken to be the version. It is ok to omit the version part (including the underscore) when it doesn't apply (e.g. in the case of recipes describing an entire BSP root file system), in which case OE-lite will simply pretend it is version "0".

Inside the recipe, the <name> is available as the variable ${PN}, while the <version> is available as ${PV}.

Language

Recipes are written in a domain-specific language defined by OE-lite. This is not as scary as it sounds. Essentially, the job of a recipe is to set a bunch of variables. Each variable has a well-defined semantic meaning to OE-lite. There are hundreds of variables, but fortunately most retrieve their value more or less automatically, and there is a lot of infrastructure for helping with defining the rest.

A few examples of variables and their meaning:

SRC_URI
Where to fetch the sources for the software.
DEPENDS
Utilities and libraries necessary to build the recipe.
EXTRA_OECONF
When using one of the autotools classes <OE-lite class>, this variable is appended to the ./configure command line in the do_configure step.

include and require

How a piece of software gets built usually doesn't change that much from version to version, so it is quite common to put most of the logic in .inc files which then get included from the recipe files. A complete recipe file can be as small as:

The require directive instructs OE-lite to look for the given file (unzip.inc in the example above) and include it at that point. It is a fatal error if the file is not found. The include directive works similar to require, but if the file cannot be found parsing continues as if the include was not present.

Syntax

The syntax and semantics of defining and manipulating variables is similar to the one used in Makefiles. For example, the right-hand side of an ordinary assignment FOO = "BAR" is not expanded until FOO is expanded, whereas the := operator causes immediate expansion of the RHS. Also, the operator += appends the RHS value to the LHS variable, but also prepends a space if the variable was non-empty.

Note, however, that OE-lite does not have the concept of variable »flavors«, and that all right-hand sides should be properly quoted strings.

See the appendix chap_syntax for a semi-formal survey of the various allowed syntactic elements.