How to check if the file contains only numeric values

Shell Programming and Scripting
1

How to check if the file contains only numeric values.

I don't want to read entire file it eats lot of cpu

Or any way which consumes less memory n cpu..

Please suggest

-S

2 
grep -cv '[0-9]' file
3

Are there more than one value per line? Integers only? Plus/minus? Octal? Hex?