Re: Breaking a table of record rows into an array

On 2024-03-13, Ed Morton <mortonspam@gmail.com> wrote:

On 3/13/2024 4:49 PM, Kaz Kylheku wrote:

On 2024-03-13, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:

Kaz Kylheku <433-929-6894@kylheku.com> writes:

On 2024-03-13, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:

arnold@freefriends.org (Aharon Robbins) writes:

In article <usqkgn$he7u$2@dont-email.me>,
Ed Morton  <mortonspam@gmail.com> wrote:

the effect of setting `NF` is
undefined behavior per POSIX and so will do different things in
different awk variants and even in 1 awk variant can behave differently
depending on whether you're setting it to a higher or lower than
original value

>
This is not true. The effect of setting NF was well defined
by the original awk book and also in POSIX.
>
Decreasing NF throws away fields. Increasing NF adds the
intervening fields with the null string as their values
and rebuilds the record.

>
I don't see that in the POSIX specification.

>
The key is this:
>
   References to nonexistent fields (that is, fields after $NF), shall
   evaluate to the uninitialized value.
>
NF is assignable, and fields after $NF do not exist. Thus if we
have four fields and set NF = 3, then $4 doesn't exist.

>
That's a bit like the argument from an old episode of the comedy TV show
"Yes, Prime Minister"

But that show is the reference model for how ISO and IEEE standarization
works.

in the UK where his aide says (paraphrased) "Some
country has done X, we must go something. War is something, therefore we
must go to war".
>
Being able to set NF to 3 does not mean you must delete $4.

The passage says that fields do not exist beyond $NF. So if NF
is 3, $4 doesn't exist.

Why not
delete $1 or $2 instead?
You'd still end up with 3 fields to satisfy the
value of NF.

Because those are less than 3, the value in NF. Those exist.
$2 and $3 exist while NF is originally 4; and continue to
exist if it is decremented to 3. Why would $2 be victimized,
when at no point had NF been less than 2?

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