Build scripts: commit only when something is staged, so make build doesn't stop when nothing changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: AllenDowney

PROJECT_BOARD.md

@@ -192,7 +192,7 @@ Pushed after chap10 (2026-10-13): both repos, one push each; student notebooks a
 
 **Released after chap27 (2026-10-13):** ModSimPySolutions and ModSimPy pushed (CI passed on both); student chapters and examples, the notebook zip and `modsim.py` regenerated; site rebuilt and published (chapter numbers, all fixes; Pages deploy checked live); short links `/minmod`, `/cdc`, `/minimize` deployed (GreenTeaPress `2f9dd77`). All 44 solution notebooks passed nbmake locally first.
 
-**Build snag:** `make build` stops when a build script has nothing new to commit (the scripts run `git commit` unconditionally and exit with its status), e.g. when the exported `chapNN.py` are unchanged. This time the steps were run by hand in the Makefile's order. Fix: make those commits conditional (`git diff --cached --quiet || git commit ...`).
+**Build snag:** `make build` stops when a build script has nothing new to commit (the scripts run `git commit` unconditionally and exit with its status), e.g. when the exported `chapNN.py` are unchanged. This time the steps were run by hand in the Makefile's order. Fix: make those commits conditional (`git diff --cached --quiet || git commit ...`). **Fixed 2026-10-13** in `chapters/build.sh`, `examples/build.sh` and `ModSimPySolutions/chapters/build.sh`.
 
 | Notebooks | Status |
 |---|---|

chapters/build.sh

@@ -4,7 +4,7 @@ python remove_soln.py
 
 # add and commit
 git add chap*.ipynb chap*.py
-git commit -m "Updating chapters"
+git diff --cached --quiet || git commit -m "Updating chapters"
 
 # build the zip file
 cd ../..; zip -r ModSimPyNotebooks.zip \
@@ -16,4 +16,4 @@ mv ModSimPyNotebooks.zip ModSimPy
 cd ModSimPy
 
 git add ModSimPyNotebooks.zip
-git commit -m "Updating the notebook zip file"
+git diff --cached --quiet || git commit -m "Updating the notebook zip file"

examples/build.sh

@@ -4,4 +4,4 @@ python remove_soln.py
 
 # add and commit
 git add *.ipynb
-git commit -m "Updating examples"
+git diff --cached --quiet || git commit -m "Updating examples"