30 chars:

    sub hexout4  {
        "@{[unpack('H*',pop)=~/../g]}"
    }
[download]

On a related note does anyone know why the sprintf format "%#x" behaves differently for 0 than for other numbers.

    printf "%#x\n", 0;
    printf "%#x\n", 1;

    __END__
    Prints:
    0
    0x1
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I guess that the behaviour comes from the C compiler that builds perl because the following gives the same results (at least where I could test it):

    int main () {

        printf("%#x\n", 0);
        printf("%#x\n", 1);

        return 0;
    }
[download]

So why is 0 treated differently?

--
John.