Also keep in mind that you may not need to initialize them at all - perl can usually figure out what you want to do. For example

my $var1;
$var1++;
print "Var1 is now $var1\n";

my $var2;
$var2 = "Foobar";
print "Var2 is now $var2\n";
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Both of the above will work fine. The values start out undefined, and in most cases (but not all) they do not need an explicit initialization.