Lua function to replace metatags in a string?

Question

(Maybe this is a recipe request for the new cookbook site.)
I'd like a function that, given a string and a LrPhoto, will search and replace tags in the string with metadata from the photo. So, given a string 'The title of this photo is {{title}}', it would return a string where {{title}} has been replaced with the LrPhoto.getRawMetadata('title') (or maybe getFormattedMetadata). I'm sure it's been written more than once. Is there one out there to be shared before I write my own?
db

Answer 1

I spent the time on this myself and don't know why I bothered asking, it was so simple. Here's what I did. First, a general-purpose function to replace any token in a string with values from a table:
-- replace any string of characters in a string that are surrounded by curly
-- braces (e.g. {foo}) with the value in the table corresponding to 'foo'.
-- will replace all tokens in braces if there are more than one
function DFB.replaceTokens( tokenTable, str )
    return str:gsub( '{(.-)}', function( token ) return tokenTable[token] end )
end
Then, if you want to do this with a photo's metadata, just pass the table that's returned from getRaw/FormattedMetadata:
line = DFB.replaceTokens(  photo:getFormattedMetadata( nil ) , line )
So if line starts out with "my caption is {caption}" and the photo's caption is 'My Photo Caption', the result is "my caption is My Photo Caption".
I use this in a simple templating system that reads an HTML template from a file and does this for each line as it reads/writes it. Works well.