From 6b670253c05fadfee50fefa4e352106a62f5fe7c Mon Sep 17 00:00:00 2001
From: Daniel Langbein <daniel@systemli.org>
Date: Fri, 15 Sep 2023 10:42:28 +0200
Subject: [PATCH] update README

---
 README.md | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/README.md b/README.md
index 8f829eb..02c0cfc 100644
--- a/README.md
+++ b/README.md
@@ -43,6 +43,8 @@ To apply the updates, continue with "Build and switch".
 sudo nixos-rebuild -I nixos-config=hosts/$(hostname)/configuration.nix switch
 ```
 
+To view changes, see section "Compare two versions of NixOS system profile".
+
 #### Option II: Build new config and activate it during next boot:
 
 ```shell
@@ -318,6 +320,24 @@ Excerpt of the result:
 
 ### Compare two versions of NixOS system profile
 
+Get latest system profile. This is the profile (usually) being active after booting the system:
+
+```shell
+ls -1 /nix/var/nix/profiles/ | sort -t'-' -n -k2 | tail -n 1
+#=> 120
+```
+
+Compare current with previous profile:
+
+```shell
+# https://stackoverflow.com/a/36641298
+prev="$(ls -1 /nix/var/nix/profiles/ | sort -t'-' -n -k2 | tail -n 2 | head -n 1)"
+curr="$(ls -1 /nix/var/nix/profiles/ | sort -t'-' -n -k2 | tail -n 1)"
+nix --extra-experimental-features nix-command store diff-closures /nix/var/nix/profiles/"${prev}" /nix/var/nix/profiles/"${curr}"
+```
+
+Compare two arbitrary system profiles:
+
 ```shell
 nix --extra-experimental-features nix-command store diff-closures /nix/var/nix/profiles/system-110-link /nix/var/nix/profiles/system-116-link
 ```