Try this FET* script:
---------------
<<forEachTiddler
script 'function extract(str, RE) {
var r = [];
str.replace(/@{2}(.+?)@{2}/g, function(a, b) { r.push(b); });
return r;
}'
write 'extract(tiddler.text).join("\n");'
>>
---------------
Keep in mind that with a large TiddlyWiki, this might take a while to
process. (Though that processing will only occur when this macro - that
is, the respective tiddler - is rendered.)
HTH.
-- F.
Minor correction:
---------------
<<forEachTiddler
script 'function extract(str, RE) {
var r = [];
str.replace(RE, function(a, b) { r.push(b); });
return r;
}'
write 'extract(tiddler.text, /@{2}(.+?)@{2}/g).join("\n");'
>>
---------------
-- F.