how about in Perl 6 being able to use require or a variant of use to be able to specify which of two versions of a given module you have to use in the script.

This already exists in Perl 5.

perldoc -f use

=item use Module VERSION LIST

If the VERSION argument is present between Module and LIST, then the
C<use> will call the VERSION method in class Module with the given
version as an argument.  The default VERSION method, inherited from
the Universal class, croaks if the given version is larger than the
value of the variable C<$Module::VERSION>.  (Note that there is not
a comma after VERSION!)
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Tony

The VERSION argument does not specify which version of a module to use, from multiple installed versions. Rather, as this snippet of documentation states: after the module has been loaded (which will be the first occurence of the module in @INC, regardless of VERSION), Perl will die if $Module::VERSION is less than the VERSION argument.

This is just like putting require 5.005; in your Perl script. It won't change which perl executable is used to run your script; it will simply die if the executable used isn't a recent enough version.

No, that checks whether you got as new of a version as you requested. It does not let you pick between multiple versions that are installed.

        - tye (but my friends call me "Tye")