You made two errors. You'd immediately see that if you tried to print the contents of $v.

• You forgot the '$' in front of the variable's name
• You need to separate the $prereq from the two colons, or Perl will treat them as the name of the variable $VERSION from the package "prereq".

This fixes it:

    my $v = "\$$prereq\::VERSION";  # LINE 115
[download]

At least, now I see the printed result:

  Found DBI version 1.15

without any warning. (I don't have the other module.)