QE Development
Yocto: How to assign variables with examples
- = A hard assignment. The variable is assigned as soon as the statement is evaluated. If the assignment contains a reference to another variable then that reference will be included in the assignment rather that the value of the reference.
- ?= Defines a variable only if it is undefined at the time of parsing.
- ??= Assignment does not occur until the end of the parsing process.
- := Immediate variable expansion
- += Appending with spaces.
- =+ Prepending with spaces.
- .= Appending without spaces.
- =. Prepending without spaces.
Assignment Using Overrides
Variables can be appended or prepended using the override style syntax. In the example below B becomes equal to “bval additional data” and C becomes equal to “additional data cval”. Note that no additional spaces are include over what is in the original variable definitions.
Removal of data can also be accomplished. In the following example FOO becomes equal to “ghi abcdef”. Note that surrounding spaces are also removed.
In the following example the value of A is set to “aval”. The value of B is set to “pre${A}post”. In other words the value of B becomes dependent on the value of A at the times it is referenced. If the value of A changes between references to B the value of B will be different at those times.
The following code includes some immediate variable assignment. The value of A becomes “test 123” as the values of A and B are unassigned at the time of As assignment.
The following code uses a soft assignment. A is only assigned if the value is currently unassigned. The code therefore results in A being given the value of “one”
The following code uses weak assignment. A is not assigned until the end of the parsing process and is therefore given a value of “two”
- Yocto cheat sheet
Yocto has a lot of variables. In the following post I’ll outline some of the variables that are commonly used in recipies.
However, one could also loopup variables in the yocto reference guide:
Variable Glossary
Variable Context
Trending Tags
Navigation Menu
Search code, repositories, users, issues, pull requests..., provide feedback.
We read every piece of feedback, and take your input very seriously.
Saved searches
Use saved searches to filter your results more quickly.
To see all available qualifiers, see our documentation .
- Notifications
One-Stop Repository for all that wish to skim through or deep-dive into Yocto Project
shantanoo-desai/yoctoproject-cheatsheet
Folders and files, repository files navigation, yocto project cheatsheet.
A summary of all things one might need to work with Yocto Project . One stop repository for Yocto since there are so many variables and CLIs to work with.
Contributing
Please feel free to add / adapt the list accordingly via PRs. As OE/Yocto Project still has a steep learning-curve, a better way would be to share resources with the community.
All hints for CLIs like bitbake , bitbake-layers , devtool etc. used within common Yocto Project development
Configuration
All variables that can be added to files like bblayers.conf or local.conf or other configuration files in Yocto.
All miscellaneous resources once can find for understanding the Yocto Project and working with it.
Documentation / Websites
- repo Command Reference
- OpenEmbedded Layers Index
- OpenEmbedded Errors Index
Repositories
- yocto-research by @davisRoman
- meta-diet layer, part of Blog by Johan Thelin (@e8johan)
- Yocto part I – baseline boot time
- Yocto part II – baseline image size
- Yocto part III – a custom meta layer
- Yocto part IV – going on a diet
- Bake 64-bit Raspberry Pi 3 images with Yocto, Openembedded
- Yocto Project YouTube Channel
- Live Coding with Yocto Project Playlist
- Paul Barker's YouTube Channel/ Rust with Yocto Project
- single 5.0.1
- Yocto Project Reference Manual »
- 13 Variable Context
- View page source
13 Variable Context
While you can use most variables in almost any context such as .conf , .bbclass , .inc , and .bb files, some variables are often associated with a particular locality or context. This chapter describes some common associations.
13.1 Configuration
The following subsections provide lists of variables whose context is configuration: distribution, machine, and local.
13.1.1 Distribution (Distro)
This section lists variables whose configuration context is the distribution, or distro.
DISTRO_NAME
DISTRO_VERSION
PACKAGE_CLASSES
13.1.2 Machine
This section lists variables whose configuration context is the machine.
TARGET_ARCH
SERIAL_CONSOLES
PACKAGE_EXTRA_ARCHS
IMAGE_FSTYPES
MACHINE_FEATURES
MACHINE_EXTRA_RDEPENDS
MACHINE_EXTRA_RRECOMMENDS
MACHINE_ESSENTIAL_EXTRA_RDEPENDS
MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS
13.1.3 Local
This section lists variables whose configuration context is the local configuration through the local.conf file.
EXTRA_IMAGE_FEATURES
BB_NUMBER_THREADS
BBINCLUDELOGS
ENABLE_BINARY_LOCALE_GENERATION
13.2 Recipes
The following subsections provide lists of variables whose context is recipes: required, dependencies, path, and extra build information.
13.2.1 Required
This section lists variables that are required for recipes.
LIC_FILES_CHKSUM
SRC_URI — used in recipes that fetch local or remote files.
13.2.2 Dependencies
This section lists variables that define recipe dependencies.
RRECOMMENDS
13.2.3 Paths
This section lists variables that define recipe paths.
13.2.4 Extra Build Information
This section lists variables that define extra build information for recipes.
DEFAULT_PREFERENCE
EXTRA_OECMAKE
EXTRA_OECONF
EXTRA_OEMAKE
PACKAGECONFIG_CONFARGS
IMAGES
VIDEO
COMMENTS
If you want to append or prepend values without an inserted space, use the ".=" and "=." operators. These operators take immediate effect during parsing. Here are some examples: B = "bval" B .= "additionaldata" C = "cval" C =. "test". The variable B contains "bvaladditionaldata" and C contains "testcval".
ALLOW_EMPTY . Specifies whether to produce an output package even if it is empty. By default, BitBake does not produce empty packages. This default behavior can cause issues when there is an RDEPENDS or some other hard runtime requirement on the existence of the package. Like all package-controlling variables, you must always use them in conjunction with a package name override, as in:
In this Yocto tutorial video, we will explore the "+=" and "=+" assignment operators, which are used for appending and prepending values to variables in Yoct...
In this video, we will cover how to use these operators by demonstrating examples in which we append, prepend, or remove strings from a variable. First, we w...
In this tutorial, we'll be discussing the Yocto Project's append and prepend operators, which are used for modifying variables in a recipe. These operators a...
Saved searches Use saved searches to filter your results more quickly
B = "pre${A}post". The following code includes some immediate variable assignment. The value of A becomes "test 123" as the values of A and B are unassigned at the time of As assignment. T = "123". A := "${B} ${A} test ${T}" The following code uses a soft assignment. A is only assigned if the value is currently unassigned.
3.4.1 Variable Formatting Variable assignment should a space around each side of the operator, e.g. FOO = "bar", not FOO="bar". ... Keep in mind that every patch submitted upstream reduces the maintainance burden in OpenEmbedded and Yocto Project in the long run, so this patch status should only be used in exceptional cases if there are genuine ...
1. The suffix underscore '_' followed by a string means that the variable, PREFERRED_PROVIDER_virtual/kernel in this case is "overridden". bitbake will use this assignment when the OVERRIDES variable contains that particular string, such as "imx6ul". Many times, if not all, the SoC architecture is set in the MACHINEOVERRIDES variable in the ...
In this video, we will learn about the different types of variable assignments in Yocto.Variables are an important concept in Yocto and are used to define va...
Yocto cheat sheet. lukas on Feb 1, 2022. Feb 3, 2022 1 min. Yocto has a lot of variables. In the following post I'll outline some of the variables that are commonly used in recipies. However, one could also loopup variables in the yocto reference guide:
One stop repository for Yocto since there are so many variables and CLIs to work with. Contributing. Please feel free to add / adapt the list accordingly via PRs. As OE/Yocto Project still has a steep learning-curve, a better way would be to share resources with the community.
In this Yocto tutorial video, we will explore two of the most commonly used assignment operators - "=" and ":=". These operators are used to assign values to...
When inheriting the systemd class, this variable specifies the systemd service name for a package. When you specify this file in your recipe, use a package name override to indicate the package to which the value applies. Here is an example from the connman recipe: SYSTEMD_SERVICE_${PN} = "connman.service".
Tour Start here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site
13 Variable Context . While you can use most variables in almost any context such as .conf, .bbclass, .inc, and .bb files, some variables are often associated with a particular locality or context. This chapter describes some common associations. 13.1 Configuration . The following subsections provide lists of variables whose context is configuration: distribution, machine, and local.
In this video we are going to learn about the ?= and ??= Variable Assignment Operators. This video explains the detail concept of setting default values in Y...
7. Reading a book on Yocto. Got to the following page, which says: BitBake provides a very easy-to-use way to write conditional metadata. It is done by a mechanism called overrides. The OVERRIDES variable contains values separated by colons (:), and each value is an item we want to satisfy conditions. So, if we have a variable that is ...
Josef looks at variables in recipes and the various forms of operations and assignments that can be used on them. Includes some notes on bbappends and bbclas...
I don't know yocto, but can tell you about the 'lifecycle': Your statement defines the environment variable ABC to the current process and, since the environment is inherited to child processes, it is also available in the direct and indirect child processes of your process. There is one gotcha: A process is allowed decide to explicitly pass a modified or even empty environment to its child ...