Simple stupid function to do python-style dict string replacement.

gistfile1.txt

-- function for doing dictionary-style replacement of varaibles
-- in a SQL string.  variables are marked in the text with ${var}
-- and replaced using a json dictionary

create or replace function replace_vars ( somestring text,
    vars JSON )
returns text
language plpgsql
immutable 
as
$f$
DECLARE newstring TEXT;
    varname TEXT;
    varval TEXT;
BEGIN
newstring := somestring;
FOR varname, varval IN 
    SELECT key, value FROM json_each_text(vars)
    ORDER BY length(key) DESC, key
    LOOP

    newstring := replace(newstring, format('${%s}',varname), varval);

END LOOP;
RETURN newstring;
END;
$f$;