Note: this relies on undocumented behavior. The behavior it depends on may be changed without warning. 
sub foo {
    my $x if 0;
    print "X is ", $x++, $/;
}

foo() for 3 .. 5;
----
X is 0
X is 1
X is 2

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My wife's blog

In reply to Re: Making a variable in a sub retain its value between calls by dragonchild
in thread Making a variable in a sub retain its value between calls by crashtest

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