You are creating two types of variables:

my $var = 10; # This is a lexical variable.
$van = 5;     # This is a package global.
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If you were dealing only with lexicals, you could do this:

{
  my $var = 10;
  my $van = 5;
  print "\$var = $var; \$van = $van\n";
}
# Here, $var and $van don't exist.
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But you're talking about resetting just those variables that start with 'v'. Don't think that way. Think in terms of using a hash:

use strict;
use warnings;

my %hash;
$hash{var} = 10;
$hash{van} = 5;
print "var = $hash{var}; van = $hash{van}\n"; 
delete hash{$_} for grep { /^v/ } keys %hash;

print "var = $hash{var}; van = $hash{van}\n";
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If you don't want to delete the keys, you could also just do this:

$hash{$_} = undef for grep { /^v/ } keys %hash;
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