== An _awk_ idiom: getting fields backwards from the end of the line

It's easy in _awk_ to get fields counting from the start of a line;
the first field is _$1_, the second field is _$2_, and so on. But
periodically I'm not interested in fields at the start of the line, I'm
interested in a field at the *end* of the line; it's much easier to see
that it's the third-last field than to carefully count how many fields
it is from the start.

(And sometimes you have a variable number of fields in a line but you
know that what you want is always Nth field from the end, in which case
counting up from the front doesn't help at all. One common case is when
a logical field can sometimes have whitespace, so awk will turn it into
a variable number of fields.)

Fortunately _awk_ has a way out: '_$_' is actually an operator (a very
high precedence one), so it takes expressions as well as just numbers,
and the _NF_ variable is the number of fields in the current line.

Because I keep forgetting this: the last field in the line is '_$(NF)_',
and '_$(NF-1)_' is the *second last* field. (Because _awk_ counts fields
from 1 instead of from 0, unlike Python and Perl.)

(Okay, technically you can use the _$[_ magical variable to make Perl
1-based, or in fact arbitrarily based. Don't.)