jq: Select range

Question

TL;DR: Given an input file with a series of keypairs, I want to select the 3rd-to-last and 4th-to-last pairs. I can get them individually, but I want to grab both at once if possible. Can this be done?

My input file is structured like this;

[
 {
  "foo": "bar",
  "foo2": "bar2"
 },
 {
  "foo3": "bar3",
  "foo4": "bar4"
 },
 {
  "foo5": "bar5",
  "foo6": "bar6"
 },
 {
  "foo7": "bar7",
  "foo8": "bar8"
 },
 {
  "foo9": "bar9",
  "foo10": "bar10"
 }
]

And my output should be

[ 
 {
  "foo3": "bar3",
  "foo4": "bar4"
 },
 {
  "foo5": "bar5",
  "foo6": "bar6"
 }
]

I know I can do jq -s '.[-3]' to get the 3rd-to-last (and swap with a 4 for the 4th-to-last) but that grabs them separately.

I thought from the documentation that jq -s '.[-3;-4]' would grab both but that throws an error.

I could grab them individually and work on each separately but that's sloppy code. Is there a cleaner way to grab both at once?

Answer 1

If you want to select ranges of values in an array, you could use the slice syntax:

<start-index>:<end-index>

Just remember that the ending index is exclusive (and not inclusive) and should be increasing order.

So to get the third/fourth from the end:

.[-4:-2]