Use seek to go to the place where you want, then print the data you want (which doesn't have to be line-formatted).

To read a record, again use seek then read it with read.

To find out where you are in a file, use tell.

If you want to avoid stdio's buffering, use sysopen, syswrite, sysseek, and sysread.

All of these functions are outlined in the perlfunc manpage, or by running perldoc -f funcname.