Refactor and tidy BOSL's shell scripts

* Fixed ShellCheck.net warnings, including
  * exit -1: https://github.com/koalaman/shellcheck/wiki/SC2242
  * cd || exit: https://github.com/koalaman/shellcheck/wiki/SC2164
  * "$foo": https://github.com/koalaman/shellcheck/wiki/SC2086
  * $(( $foo )): https://github.com/koalaman/shellcheck/wiki/SC2004
  * grep | wc -l: https://github.com/koalaman/shellcheck/wiki/SC2126
* Use arrays instead of unquoted strings for loops and command arguments
* Use (( ... )) arithmetic context instead of string comparisons
* Use bash's built-in regex support instead of grep+sed+awk
* Write errors to stderr

scripts/make_tutorials.sh

@@ -1,40 +1,38 @@
 #!/bin/bash
 
-FORCED=""
-FILES=""
-DISPMD=""
+DISPMD=0
+GEN_ARGS=()
+FILES=()
 for opt in "$@" ; do
-  case $opt in
-    -f ) FORCED=$opt ;;
-    -d ) DISPMD=$opt ;;
-    -* ) echo "Unknown option $opt"; exit -1 ;;
-    * ) FILES="$FILES $opt" ;;
+  case "$opt" in
+    -f ) GEN_ARGS+=(-f) ;;
+    -d ) DISPMD=1 ;;
+    -* ) echo "Unknown option $opt" >&2; exit 1 ;;
+    * ) FILES+=("$opt") ;;
   esac
 done
 
-if [[ "$FILES" != "" ]]; then
-    PREVIEW_LIBS="$FILES"
-else
-    PREVIEW_LIBS="Shapes2d Shapes3d Transforms Distributors Mutators Attachments Paths FractalTree"
+if (( ${#FILES[@]} == 0 )); then
+    FILES=(Shapes2d Shapes3d Transforms Distributors Mutators Attachments Paths FractalTree)
 fi
 
-dir="$(basename $PWD)"
-if [ "$dir" = "BOSL2" ]; then
-    cd BOSL2.wiki
-elif [ "$dir" != "BOSL2.wiki" ]; then
-    echo "Must run this script from the BOSL2 or BOSL2/BOSL2.wiki directories."
+# Try to cd to the BOSL2.wiki directory if run from the BOSL2 root
+if [[ "$(basename "$PWD")" != "BOSL2.wiki" ]]; then
+  if ! cd BOSL2.wiki; then
+    echo "BOSL2.wiki directory not found, try running from the BOSL2 or BOSL2/BOSL2.wiki directory" >&2
     exit 1
+  fi
 fi
 
 rm -f tmp_*.scad
-for base in $PREVIEW_LIBS; do
-    base="$(basename $base .md)"
+for base in "${FILES[@]}"; do
+    base="$(basename "$base" .md)"
     mkdir -p images/tutorials
-    rm -f images/tutorials/${base}_*.png images/tutorials/${base}_*.gif
-    echo "$base.md"
-    ../scripts/tutorial_gen.py ../tutorials/$base.md -o Tutorial-$base.md $FORCED -I images/tutorials/ || exit 1
-    if [ "$DISPMD" != "" ]; then
-        open -a Typora Tutorial-$base.md
+    rm -f "images/tutorials/${base}"_*.png "images/tutorials/${base}"_*.gif
+    echo "${base}.md"
+    ../scripts/tutorial_gen.py "../tutorials/${base}.md" -o "Tutorial-${base}.md" "${GEN_ARGS[@]}" -I images/tutorials/ || exit 1
+    if (( DISPMD )); then
+        open -a Typora "Tutorial-${base}.md"
     fi
 done