macos: hot corners and tap to click, and a way to find the next key

Three settings this account has always set by hand on every new Mac, now in the
script that exists for exactly that: the bottom-right hot corner sleeping the
display, tap to click, and three-finger drag on an external trackpad -- the
last a gap, since the script set it only for the built-in one.

Each of those is written in more than one place because macOS keeps them in
more than one place: an external Magic Trackpad has its own domain, and the
login window reads com.apple.mouse.tapBehavior rather than either of them,
per-host for this machine and globally for any other. Setting one and not the
others is why tap to click sometimes survives a reboot and sometimes does not.

bin/macos-defaults-diff is the general answer: snapshot, change one setting,
and it prints what moved, including the -currentHost domains a plain
`defaults read` never shows. It flushes cfprefsd first, since a change made
seconds earlier can otherwise be missing from the read meant to reveal it, and
it says plainly when nothing changed -- anything behind Privacy & Security
lives in the SIP-protected TCC database and cannot be scripted at all.

1 files changed, 99 insertions, 0 deletions

diff --git a/bin/macos-defaults-diff b/bin/macos-defaults-diff
new file mode 100755
index 0000000..14274e3
--- /dev/null
+++ b/bin/macos-defaults-diff
@@ -0,0 +1,99 @@
+#!/bin/bash
+
+# Find the `defaults` key behind a setting you changed in System Settings, so it
+# can go in macos-defaults.sh instead of being remembered.
+#
+#   macos-defaults-diff            snapshot, wait while you change one setting,
+#                                  then print what moved
+#   macos-defaults-diff snap       take the snapshot only
+#   macos-defaults-diff show       compare now against the last snapshot
+#
+# It reads both the global domains and the per-host ones (`-currentHost`), which
+# is where several trackpad, mouse and font settings live and which a plain
+# `defaults read` never shows.
+#
+# Change ONE setting at a time. macOS writes unrelated keys constantly -- window
+# positions, recent items, sidebar widths -- so a diff after three changes is
+# mostly noise with your key hidden in it.
+#
+# Quit System Settings before the second snapshot. It holds changes in memory
+# and cfprefsd may not have written them yet; the line below flushes that cache.
+#
+# Runs under macOS's /bin/bash 3.2.
+
+set -euo pipefail
+
+if [[ "$(uname)" != "Darwin" ]]; then
+    >&2 echo "macos-defaults-diff: macOS only"
+    exit 1
+fi
+
+dir="${TMPDIR:-/tmp}/macos-defaults-diff"
+mkdir -p "${dir}"
+
+snapshot() {
+    local tag="$1"
+    # cfprefsd caches writes; without this a change made seconds ago can be
+    # missing from the read that is supposed to reveal it.
+    killall cfprefsd 2>/dev/null || true
+    sleep 1
+    defaults read > "${dir}/${tag}.txt" 2>/dev/null || true
+    defaults -currentHost read > "${dir}/${tag}-host.txt" 2>/dev/null || true
+}
+
+report() {
+    if [[ ! -f "${dir}/before.txt" ]]; then
+        >&2 echo "macos-defaults-diff: no snapshot yet -- run 'macos-defaults-diff snap' first"
+        exit 1
+    fi
+    snapshot after
+    local found=""
+    if ! diff -u "${dir}/before.txt" "${dir}/after.txt" > "${dir}/delta.txt" 2>&1; then
+        found=y
+        echo "=== global domains"
+        grep -E '^[+-]' "${dir}/delta.txt" | grep -vE '^(\+\+\+|---)' | sed 's/^/  /'
+    fi
+    if ! diff -u "${dir}/before-host.txt" "${dir}/after-host.txt" > "${dir}/delta-host.txt" 2>&1; then
+        found=y
+        echo "=== this host only -- these need 'defaults -currentHost write'"
+        grep -E '^[+-]' "${dir}/delta-host.txt" | grep -vE '^(\+\+\+|---)' | sed 's/^/  /'
+    fi
+    if [[ -z "${found}" ]]; then
+        echo "nothing changed."
+        echo "Some settings are not in defaults at all: anything behind Privacy &"
+        echo "Security lives in the SIP-protected TCC database, and a few panes use"
+        echo "private APIs. Those cannot be scripted -- note them in macos-defaults.sh"
+        echo "as manual steps instead."
+        return
+    fi
+    echo
+    echo "The domain is the nearest heading above the changed line in:"
+    echo "  ${dir}/delta.txt"
+    echo "Write it as: defaults write <domain> \"<key>\" -bool/-int/-string <value>"
+    echo "then add it to macos-defaults.sh, and restart whatever owns it"
+    echo "(killall Dock, killall Finder, or log out)."
+}
+
+case "${1:-}" in
+    snap)
+        snapshot before
+        echo "snapshot taken. Change one setting, then: macos-defaults-diff show"
+        ;;
+    show)
+        report
+        ;;
+    "")
+        snapshot before
+        echo "Snapshot taken. Now change ONE setting in System Settings, quit it,"
+        printf 'then press Enter: '
+        read -r _
+        report
+        ;;
+    -h|--help)
+        sed -n '3,21p' "$0" | sed 's/^# \{0,1\}//'
+        ;;
+    *)
+        >&2 echo "macos-defaults-diff: unknown argument: $1"
+        exit 1
+        ;;
+esac