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/run_tests.sh

@@ -1,35 +1,31 @@
 #!/bin/bash
 
-if [ "$(uname -s)" != "Darwin" ]; then
-    OPENSCAD=openscad
-else
+OPENSCAD=openscad
+if [ "$(uname -s)" == "Darwin" ]; then
     OPENSCAD=/Applications/OpenSCAD.app/Contents/MacOS/OpenSCAD
 fi
 
-if [ "$*" != "" ] ; then
-    INFILES="$*"
-else
-    INFILES="tests/test_*.scad"
+INFILES=("$@")
+if (( ${#INFILES[@]} == 0 )); then
+    INFILES=(tests/test_*.scad)
 fi
 
 OUTCODE=0
-for testscript in $INFILES ; do
-    repname="$(basename $testscript | sed 's/^test_//')"
-    testfile="tests/test_$repname"
-    if [ -f "$testfile" ] ; then
-        ${OPENSCAD} -o out.echo --hardwarnings --check-parameters true --check-parameter-ranges true $testfile 2>&1
+for testfile in "${INFILES[@]}"; do
+    if [[ -f "$testfile" ]] ; then
+        repname="$(basename "$testfile" | sed 's/^test_//')"
+        "${OPENSCAD}" -o out.echo --hardwarnings --check-parameters true --check-parameter-ranges true "$testfile" 2>&1
         retcode=$?
-        res=$(cat out.echo)
-        if [ $retcode -eq 0 ] && [ "$res" = "" ] ; then
+        output=$(cat out.echo)
+        if (( retcode == 0 )) && [[ "$output" = "" ]]; then
             echo "$repname: PASS"
         else
             echo "$repname: FAIL!"
-            cat out.echo
-            echo
-            OUTCODE=-1
+            echo "$output"
+            OUTCODE="$retcode"
         fi
         rm -f out.echo
     fi
 done
-exit $OUTCODE
+exit "$OUTCODE"