kubectl: kubectl diff doesn’t handle quoted options in KUBECTL_EXTERNAL_DIFF correctly

What happened?

I tried to make a diff ignoring lines matching a regex which includes special characters and thus has to be quoted:

KUBECTL_EXTERNAL_DIFF="diff -I\"^  generation: [0-9]\+$\"" kubectl diff -f filename.yaml

The matching line was not ignored in the output.

To get to the bottom of this I tried it with KUBECTL_EXTERNAL_DIFF="diff -Igeneration" and the matching change was successfully ignored, however when I added quotes like "diff -I\"generation\"" or 'diff -I"generation"' it failed to ignore the line.

What did you expect to happen?

kubectl diff handles the quoting correctly so that these are equivalent:

KUBECTL_EXTERNAL_DIFF="diff -Igeneration"
KUBECTL_EXTERNAL_DIFF="diff -I\"generation\""
KUBECTL_EXTERNAL_DIFF='diff -I"generation"'

It thus allows for special characters in the KUBECTL_EXTERNAL_DIFF command options.

How can we reproduce it (as minimally and precisely as possible)?

Try ignoring a change in the diff by using a quoted string inside KUBECTL_EXTERNAL_DIFF.

Anything else we need to know?

No response

Kubernetes version

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"23", GitVersion:"v1.23.3", GitCommit:"816c97ab8cff8a1c72eccca1026f7820e93e0d25", GitTreeState:"archive", BuildDate:"2022-01-27T18:26:18Z", GoVersion:"go1.17.6", Compiler:"gc", Platform:"linux/amd64"}

Cloud provider

OS version

$ cat /etc/os-release
NAME="Arch Linux"
PRETTY_NAME="Arch Linux"
ID=arch
BUILD_ID=rolling
ANSI_COLOR="38;2;23;147;209"
HOME_URL="https://archlinux.org/"
DOCUMENTATION_URL="https://wiki.archlinux.org/"
SUPPORT_URL="https://bbs.archlinux.org/"
BUG_REPORT_URL="https://bugs.archlinux.org/"
LOGO=archlinux-logo
$ uname -a
Linux hostname 5.16.8-arch1-1 kubernetes/kubernetes#1 SMP PREEMPT Tue, 08 Feb 2022 21:21:08 +0000 x86_64 GNU/Linux

Install tools

No response

Container runtime (CRI) and and version (if applicable)

No response

Related plugins (CNI, CSI, …) and versions (if applicable)

No response