FUNCTION extract_str, line, char1, char2
;
; extract sub-string of line that is between char1 and char2
;
   pos_char1 = strpos(line,char1)
   pos_char2 = strpos(line,char2)
   lenght_to_extract = pos_char2-pos_char1-1
   
   IF lenght_to_extract LE 0 THEN BEGIN
      print, 'No sub-string in', line, ' between in : ', char1, char2
      return,  -1
   ENDIF 

   return, STRMID(line, pos_char1+1, lenght_to_extract)
END