Sorry, I only have counters with GPIB interface, 5335A and 5370B. The data output formats, always ending with <cr> <lf>, is described in their manuals.
If you have a 34401A DMM, it has a TALK ONLY mode over its RS232 mode also (set address 31), intended for printer dump, but this can also be sent to a PC with serial interface and PROCOMM -alike monitor program. And the 34401A also measures frequency. That would be the same thing as with the 53131/132 universal counters, which also had an RS232. Modern counters probably lack that old serial interface, as they have USB instead.
Again, there is no real standard for the output string.
Frank
PS: maybe the screen dump from TALK ONLY over GPIB is what you are looking for.