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Bitbqke syntax has similarities to several other languages but also has some unique features. This section describes the used syntax and operators as well as provides examples. This assignment occurs immediately as the statement is parsed. It is a “hard” assignment. Doing so allows you to use values that contain the double quote character: They do not suppress variable expansions.

The following assignments result in A containing “aval” and B evaluating to “preavalpost”. Instead, expansion is deferred until the variable assigned to is actually used. The result depends on the current values of the referenced variables. The following example should clarify this behavior: This type of assignment allows you to define a variable if it is suer when the statement is parsed, but to leave the value alone if the variable has a value.

Here is bitbakke example: Consequently, if multiple “? This assignment behaves identical to “? Consequently, when multiple “?? These operators insert manuaal space between the current value and prepended or appended value. Here are some examples: When you use this syntax, no spaces are inserted. Specifying a value for removal causes all occurrences of that value to be removed from the variable. Surrounding spaces and spacing are preserved.

It is a way of tagging extra information onto a variable. All the standard syntax operations previously mentioned work for variable flags except for override style syntax i.

The flags are immediately set to “abc” and “”, respectively.

You can simply start using them. One extremely common application is to attach some brief documentation to a BitBake variable as follows: The following lines select the values of a package name and its version number, respectively: Doing so manua cause BitBake to not recognize the path since BitBake does not expand this character in the same way a shell would.

Additionally, underscores are not permitted in override names as they are used to separate overrides from each other and from the variable name.

To better understand this, consider the following example: This section presents some common scenarios along with explanations for variable interactions that typically confuse users.

Consider the following example: Manua that spaces maual not appended. For example, suppose you have a piece of common functionality such as a task definition that you want to share between more than one recipe. BitBake only supports this directive when used within recipe and class files i.

For example, you can easily abstract out the tasks involved in building a package that uses Autoconf and Automake and put those bitbakf into a class file bitbale then have your recipe inherit that class file.


The class file would contain common functionality for using Autotools that could be shared across recipes: One way to achieve a conditional inherit in this case is to use overrides: This directive uer BitBake to parse whatever file you specify, and to insert that file at that location. Doing so makes sure that an error is produced if the file cannot be found. Thus, any file you require is inserted into the file that is being parsed at the location of the directive.

BitBake only supports this bitbame when used within a configuration file. Use spaces to separate the classes. BitBake supports these types of functions: They can also be called by other shell functions.

Here is an example shell function definition: You should not use Bash-specific script bashisms. It can also be used to modify functions inherited from classes.

Bitbake Cheat Sheet

Also in these types of functions, the datastore “d” is a global variable and is always automatically available. This behavior is intentional in order to allow you to freely set variable values to expandable expressions without having them expanded prematurely.

Examples of Python functions are utility functions that you intend to call from in-line Python or from within other Python functions. Consequently, you must pass it in as a parameter to the function.

You do not need to import them. To do this, you jser define special Python functions, called anonymous Python functions, that run at the end of parsing.

For example, the following conditionally sets a variable based on the value of another variable: If a recipe contains many anonymous functions, they run in the same order as they are defined within the recipe. As an example, consider the following snippet: Just as in the second snippet, the values set for the variables within the anonymous functions become available to tasks, which always run after parsing.

In this basic scenario, your recipe inherits the task function as defined in the class. However, if it redefines the function, there is no means for it to call the class version of the function. If you do not set up these conditions, you are limited to using one function or the other.

Tasks are only supported in recipes and classes i.

BitBake User Manual

Here is an example that shows how to define a task and declare some dependencies: This is because BitBake considers the task “up-to-date” after that initial run.

For example, to delete the example task used in the previous sections, you would use: Loading something from the bitbke into the datastore previous step only makes it available in the datastore. If doing so results in unnecessary rebuilds of tasks, you can whitelist the variable so that the setscene code ignores the dependency when it creates checksums. BitBake reads and writes varflags to the datastore using the following command forms: In other words, you can set, append, and prepend varflags just like variables.


Tasks support a number of these flags which control various functionality of ueer task: Directories that already exist are removed and recreated to empty them. Directories that already exist are left as is.

The last directory listed is used as the current working directory for the task.

Only one task may hold a lockfile, and any task that attempts to lock an already locked file will block until the lock is released. You can use this variable flag to accomplish mutual exclusion.

This can cause unnecessary rebuilding if you are not careful. This varflag is useful when your build host has a large number of cores but certain tasks need to be rate-limited due to various kinds of resource constraints e.

As an example, OpenEmbedded uses this flag to allow machine-specific tasks. Adding variables to this list is useful, for example, when a function refers to a variable in a manner that does not allow BitBake to automatically determine that the variable is referred to. Events are triggered at certain points during operation, such as the beginning of operation against a given recipe i. The intent is to make it easy to do things like email notification on build failures.

This event handler gets called every time an event matching the eventmask is triggered. A global variable “e” is defined, which represents the current event. The global datastore is available as “d”. In legacy code, you might see “e.

However, realize that “e. For example, “BuildStarted” and “BuildCompleted” events run before any tasks are executed so would be in the global configuration datastore namespace. No recipe-specific metadata exists in that namespace. Task events run in the actual tasks in question consequently have recipe-specific and task-specific contents.

These events run in the worker context and are discarded at the end of task execution. The following events are the most common kinds of events that most metadata might have an interest in viewing: You can see multiple such events when each of the workers parse the base configuration or if the server changes configuration and reparses. Any given datastore only has one such event executed against it, however.

Fires at regular time intervals of one second. This event is useful for activities such as system state monitoring. Fired when BitBake is about to start parsing recipes. This event’s “total” attribute represents the number of recipes BitBake plans to parse. Fired as parsing progresses.

This event’s “current” attribute is the number of recipes parsed as well as the “total” attribute. Fired when parsing is complete.