Some people like to differentiate "doesn't have a value yet"

my $x;
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from "has the value undef (or false)

my $x = undef;
my $x = 0;
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Perl, of course, doesn't case. It's stylistic semantics.

Now, if you do the following, it's a bit silly:

my $x = undef;
if (cond()) {
   $x = f();
} else {
   $x = g();
}
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