Several problems. First, <=> is a three-state operator. It has different return values for less than comparisons, greater than, and equal to. It's primarily used for numeric comparisons in sort routines. You should be using !=

The next problem is that you cannot chain 1||2||3||4||5 like that. That's like saying "If $expire is not equal to 1, or if two, or if three, or if four, etc." In other words, the comparison only binds to $expire != 1.

To write that correctly, the way you're trying to test, it would be:

if( $expire != 1 or $expire != 2 or $expire != 3...... )
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...and so on. But how about this instead?

if(    $expire != int $expire
    or $expire < 1
    or $expire > 14 
) {
    die "Don't tamper with me!\n";
}
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You could also do it like this, using a hash slice:

my %test;
@test{ 1 .. 14 } = ();
unless( exists $test{$expire} ) {
    die "Don't tamper with me!\n";
}
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In all my examples, I've assumed that you want to reject non-integers.