As Atari911 said, you can use watch along with cat to do this. Use

watch cat <filename>

this will output the contents of the file given by filename every 2 seconds to standard output. To change the interval for updating the output to something like 1 second(you can't reduce beyond 0.1), you can use

watch -n 1 cat <filename>

I am using cat to output the complete file, you could tail but that would only give you the last n lines of the file, where n is 10 by default.

Refer to the manual page of watch for more info.