If you have pro package of wp all import you may have come across the data export section. when you figure out the syntax for creating exports. it is very easy to configure.

For the basic fields you can just drag and drop the fields from right hand panel. I am creating a export for user data here. custom export fields can be used to combine and modify data.

This user data was imported from legacy system. I have imported the legacy system user id along with it. when exporting the data I wanted to export legacy id if there is one and if it’s a new user I wanted to prefix ‘w’ to the WordPress id.

Inside functions editor you can define the function to modify data and return them. once done you need to click on “save function” button and save the code.

Here I am selecting ‘custom export field’ option. inside squire brackets you can call the PHP function that returns the data for field. Note that function should be inside squire brackets and WordPress variables should be in curly braces.

[get_user_id({ID},{Old user ID})]

If you have got any issues on getting the export working, let me know in comments. cheers.