Use of !!

[arnold]

Hi.

<pjfarley3@earthlink.net> wrote:

> Thanks for the enlightenment Arnold.
>
> So if I understand your explanation correctly,  the phrase -!!-""
> translates to this sequence of operations:
>
> 1.    -""     Minus the empty string, becomes -0 which is still just zero
> 2.    !0      Not 0 becomes 1
> 3.    !1      Not 1 becomes zero
> 4.    -0      Minus 0 which is still just 0
>
> So if I am understanding correctly, the phrase -!!-"" is just a convoluted
> way to say "zero"?

Exactly: 

        $ for i in nawk mawk mksawk "busybox awk" gawk
        > do echo === $i
        > $i 'BEGIN { printf("%d\n", (-!!-"")) }'
        > done
        === nawk
        0
        === mawk
        0
        === mksawk
        0
        === busybox awk
        0
        === gawk
        0

Arnold