When we just want to replace a specific file from the filesystem, we can use the recipetool command-line utility to automatically create the bbappend file for us. For this to work, the package needs to have been previously built and included on a target image. The syntax to use is:

$ recipetool appendfile </path/to/layer> </path/to/file/in/target> <new-file> 

A typical file to replace is the /etc/network/interfaces file that contains the network settings. We can add an append file to meta-custom to replace it with a new version with:

$ recipetool appendfile /opt/yocto/fsl-community-bsp/sources/meta-custom/ /etc/network/interfaces interfaces-new