Embedded Linux Development using Yocto Projects - Second Edition

Defining executable metadata

Metadata recipes (.bb) and class files (.bbclass) can use Shell Script code as follows:

do_mytask () {    echo "Hello, world!"}

This is essentially identical to setting a variable, except that this variable happens to be an executable shell code. It is important to be careful when writing shell script code as we should not use shell-specific code such as bash or zsh. When in doubt, a good way to test if our code is safe is to use the dash shell to test it.

Another way to inject code is by using Python code, as shown:

python do_printdate () {    import time    print time.strftime('%Y%m%d', time.gmtime())}

This is similar to the previous code but flags it as Python so that BitBake knows it is Python code and runs it accordingly. ...