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.)
awk has a way out: '
$' is actually an operator (a very
high precedence one), so it takes expressions as well as just numbers,
NF variable is the number of fields in the current line.
Because I keep forgetting this: the last field in the line is '
$(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.)