Re: [bug-gawk] Postdecrementing $NF

[Manuel Collado]

El 08/09/2013 19:30, Andrew J. Schorr escribió:
> On Sun, Sep 08, 2013 at 02:56:52AM +0200, Adam Zieliński wrote:
> > $NF-- (or even $(NF--) ) - doesn't seem to work as intended.
>
> The '$' has higher priority then '--', so I believe $NF-- is equivalent to
> ($NF)--, which is effectively equivalent to $NF.
>
> > Instead of giving me a field value and decrementing FN after that,
> > it converts field value to number and then decrements it.
> >
> > Doing the same via variable set to NF works perfectly.
>
> However, there does appear to be a problem with $(NF--).  Using current
> git sources:
>
>     bash-4.1$ echo 1 2 3 4 | gawk '{x = $(NF--); print x; print NF}'
>
>     3

Possible explanation: (NF--) returns the "original NF" *after* decrementing 
NF. So the last field is effectively hidden when $(original NF) is evaluated.

> Compare to:
>
>     bash-4.1$ echo 1 2 3 4 | gawk '{x = $NF; NF--; print x; print NF}'
>     4
>     3
>
> and
>
>     bash-4.1$ echo 1 2 3 4 | gawk '{i = NF; x = $(i--); print x; print i}'
>     4
>     3
>
> I don't see any errors from valgrind.  I haven't looked further for the
> cause of this bug...
>
> Regards,
> Andy

Regards,

--
Manuel Collado - http://lml.ls.fi.upm.es/~mcollado