Further reduced, I don't know.

But I find using explicit min and max adds more clarity, and newer Perls allow ternary° expressions "chained comparisons" a < x < b :

C:\tmp\e>perl
use List::Util qw( min max );
($a,$b) = (3,7);
print "$_ is inside: ", min($a,$b) <= $_ <= max($a,$b),"\n"  for 2..8
__END__
2 is inside:
3 is inside: 1
4 is inside: 1
5 is inside: 1
6 is inside: 1
7 is inside: 1
8 is inside:
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Using the spaceship that way is too clever for me.

°) not sure if that's the right term

update: corrected. see perlop#precedence for more.