Duplicate content from one field to another

Problem

You want to change the field settings on a field so they are different for two separate templates which are currently using the same field. So you need to end up with two separate fields: eg. body1 and body2, each with different settings. The problem is that there is already a considerable amount of content populated into the field in both templates.

Solution

Use ProcessWire API to migrate the content so it exists in both fields, then you can remove one field from one template and the other field from the other template:

// this duplicates the content in fieldname1 into fieldname2 for all pages with
// the template called: templatename
$source = "fieldname1";
$destination = "fieldname2";
$template = "templatename";

foreach($pages->find("template=$template") as $p) {
    // set outputFormatting to 'false' so the plain value is copied
    $p->of(false);
    $p->$destination = $p->$source;
    $p->save($destination);
}

Resources