According to the standards, you can't with test... and [ ... ],
but in [[ ... ]], < and > are string comparison operators. The -lt and -gt operators perform numeric comparisons in all three forms of these testing methods.

In bash, the < and > are string comparisons in test ... and [ ... ]. In ksh, the < and > will be treated as redirection operators, not string comparisons. I.e., in ksh:

Code:

if [ 100 > 200 ]
then echo gt
else echo not gt
fi

will print gt because 100 is not an empty string and will create a file named 200 because > is a redirection operator. But in bash, this same code will print not gt and will not create a file. Both of these behaviors conform to the standards because the standards don't specify any meaning for < and > in these two cases.

=================
I take part of this back. Despite what the bash man page says, at least on Mac OS X, bash and ksh both treat < and > as redirection operators in test and [.