diff --git a/.github/workflows/bats.yml b/.github/workflows/bats.yml
index 014dfc2..97a9697 100644
--- a/.github/workflows/bats.yml
+++ b/.github/workflows/bats.yml
@@ -4,8 +4,20 @@ on:
   push:
     branches:
       - main
+    paths:
+      - "**/*.sh"
+      - "tests/**"
+      - ".gitmodules"
+      - "!demo/**"
+      - ".github/workflows/bats.yml"
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review]
+    types: [ready_for_review, synchronize]
+    paths:
+      - "**/*.sh"
+      - "tests/**"
+      - ".gitmodules"
+      - "!demo/**"
+      - ".github/workflows/bats.yml"
   workflow_dispatch:
 
 permissions:
diff --git a/.github/workflows/shellcheck.yml b/.github/workflows/shellcheck.yml
index 50856ce..9faa96d 100644
--- a/.github/workflows/shellcheck.yml
+++ b/.github/workflows/shellcheck.yml
@@ -4,8 +4,16 @@ on:
   push:
     branches:
       - main
+    paths:
+      - "**/*.sh"
+      - ".shellcheckrc"
+      - ".github/workflows/shellcheck.yml"
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review]
+    types: [ready_for_review, synchronize]
+    paths:
+      - "**/*.sh"
+      - ".shellcheckrc"
+      - ".github/workflows/shellcheck.yml"
   workflow_dispatch:
 
 permissions: {}
diff --git a/.github/workflows/shfmt.yml b/.github/workflows/shfmt.yml
index 0f6b95b..53920fd 100644
--- a/.github/workflows/shfmt.yml
+++ b/.github/workflows/shfmt.yml
@@ -4,8 +4,14 @@ on:
   push:
     branches:
       - main
+    paths:
+      - "**/*.sh"
+      - ".github/workflows/shfmt.yml"
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review]
+    types: [ready_for_review, synchronize]
+    paths:
+      - "**/*.sh"
+      - ".github/workflows/shfmt.yml"
   workflow_dispatch:
 
 permissions: {}
diff --git a/.github/workflows/system-tests-demo.yml b/.github/workflows/system-tests-demo.yml
index e66e682..4dde1df 100644
--- a/.github/workflows/system-tests-demo.yml
+++ b/.github/workflows/system-tests-demo.yml
@@ -1,6 +1,17 @@
 name: System Tests Demo
 
 on:
+  push:
+    branches:
+      - main
+    paths:
+      - "**/*.sh"
+      - ".github/workflows/system-tests-demo.yml"
+  pull_request:
+    types: [ready_for_review, synchronize]
+    paths:
+      - "**/*.sh"
+      - ".github/workflows/system-tests-demo.yml"
   workflow_dispatch:
 
 jobs:
@@ -19,10 +30,9 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 1
-          submodules: recursive
 
       - name: Install GNU tools on macOS
-        if: matrix.os == 'macos-latest' && matrix.install_gnu_tools == 'true'
+        if: ${{ matrix.os == 'macos-latest' && matrix.install_gnu_tools }}
         run: |
           bin/gnu-install.sh
 
@@ -30,4 +40,5 @@ jobs:
         run: echo "ASSUME_GNU=${{ matrix.install_gnu_tools }}" >> $GITHUB_ENV
 
       - name: Run all demos
-        run: demo/all-demos.sh
+        run: |
+          demo/all-demos.sh
diff --git a/demo/all-demos.sh b/demo/all-demos.sh
index bea70b6..2070040 100755
--- a/demo/all-demos.sh
+++ b/demo/all-demos.sh
@@ -5,12 +5,14 @@
 
 SCRIPT_DIR="$(dirname "$(realpath "${BASH_SOURCE[0]}")")"
 declare -r SCRIPT_DIR
+# shellcheck source=/dev/null
+source "${SCRIPT_DIR}/../lib_init.sh"
 
 # Find all -demo.sh files in the demo directory and run them.
 for demo_script in "${SCRIPT_DIR}"/*-demo.sh; do
   if [[ -f "${demo_script}" ]]; then
     echo "Running demo: ${demo_script}"
     "${demo_script}"
-    echo
+    echo "Result of demo: ${demo_script}: ${?}"
   fi
 done
diff --git a/demo/gnucompat-demo.sh b/demo/gnucompat-demo.sh
index 79ffe6f..74f34f3 100755
--- a/demo/gnucompat-demo.sh
+++ b/demo/gnucompat-demo.sh
@@ -66,7 +66,7 @@ function demo_sed() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     local -r sed_script='s/World/GNU/g'
     # This command will fail if the GNU version of `sed` is not available.
     echo "${input}" | "${SED}" --regexp-extended "${sed_script}"
@@ -84,7 +84,7 @@ function demo_awk() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # shellcheck disable=SC2016
     local -r awk_script='{ print "Hello, GNU!" }'
     # This command will fail if the GNU version of `sed` is not available.
@@ -104,7 +104,7 @@ function demo_grep() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     local -r grep_pattern="World"
     # This command will fail if the GNU version of `grep` is not available.
     echo "${input}" | "${GREP}" --only-matching "${grep_pattern}"
@@ -122,7 +122,7 @@ function demo_sort() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `sort` is not available.
     echo "${input}" | "${SORT}" --ignore-leading-blanks
     ;;
@@ -136,7 +136,7 @@ function demo_date() {
   echo "DATE Demo:"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `date` is not available.
     "${DATE}" --utc
     ;;
@@ -151,7 +151,7 @@ function demo_xargs() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `xargs` is not available.
     echo "${input}" | "${XARGS}" --no-run-if-empty echo
     ;;
@@ -167,7 +167,7 @@ function demo_cut() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `cut` is not available.
     echo "${input}" | "${CUT}" --characters=3
     ;;
@@ -183,7 +183,7 @@ function demo_head() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `head` is not available.
     echo "${input}" | "${HEAD}" --lines=1
     ;;
@@ -199,7 +199,7 @@ function demo_tail() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `tail` is not available.
     echo "${input}" | "${TAIL}" --lines=1
     ;;
@@ -215,7 +215,7 @@ function demo_tr() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `tr` is not available.
     echo "${input}" | "${TR}" --delete ' '
     ;;
@@ -231,7 +231,7 @@ function demo_uniq() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `uniq` is not available.
     echo "${input}" | "${UNIQ}" --count
     ;;
@@ -247,7 +247,7 @@ function demo_wc() {
   local -r input="  Hello, World!"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `wc` is not available.
     echo "${input}" | "${WC}" --words
     ;;
@@ -261,25 +261,26 @@ function demo_diff() {
   echo "DIFF Demo:"
 
   local -r input1="Hello, World!"
-  local -r input2="Hello, Universe!"
   local -r file1="/tmp/file1.txt"
-  local -r file2="/tmp/file2.txt"
 
+  # We just need one file, as the test is just about the command execution,
+  # not the actual diff output. This spares us the need to handle different
+  # exit codes (0 for no difference, 1 for difference, 2 for error).
   echo "${input1}" >"${file1}"
-  echo "${input2}" >"${file2}"
 
   case "${ASSUME_GNU}" in
-  yes)
+  yes | true)
     # This command will fail if the GNU version of `diff` is not available.
-    "${DIFF}" --brief "${file1}" "${file2}"
+    "${DIFF}" --normal "${file1}" "${file1}"
     ;;
   *)
-    "${DIFF}" "${file1}" "${file2}"
+    "${DIFF}" "${file1}" "${file1}"
     ;;
   esac
 }
 
 function demo_all() {
+  echo "Running all demos, assuming GNU available: ${ASSUME_GNU}."
   demo_sed
   demo_awk
   demo_grep