Sorry, I don't trully understand the question.

But the asnwer is the same :) Use DB, build index on the files, content and use SQL:LIKE to extract.

HINT:
TABLE STRUCTURE:
ID(PRIMARY KEY,LONG)
FILE_NAME(TEXT)
STR_NUMBER(LONG) # - STRING NUMBER IN FILE
STR_DATA(TEXT) # - STRING ¹ STR_NUMBER FROM FILE_NAME

AND SQL: SELECT FILE_NAME, STR_NUMBER FROM TABLE WHERE (place UCASE here if DB casedependent)STR_DATA LIKE %REGEXP_HERE%