fix: resolve shellcheck warnings in COMMON and fix CI path

- Add shell directive to COMMON (SC2148)
- Quote variables, fix backticks/expr, fix -o in [ ] (SC2086/SC2006/SC2003/SC2166)
- Fix pattern expansion quoting in cmp_substr (SC2295)
- Quote basename argument (SC2086)
- Fix broken echo strings in error message
- Remove unused TESTS_DIR variable
- Add SC2034 disable comments for variables used by sourcing scripts
- Update SHELLCHECK_OPTS path to test/ so shellcheck can follow COMMON source

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: andy5995

.github/workflows/shellcheck.yml

@@ -21,4 +21,4 @@ jobs:
       - name: Run ShellCheck
         uses: ludeeus/action-shellcheck@master
         env:
-          SHELLCHECK_OPTS: -x -P $GITHUB_WORKSPACE
+          SHELLCHECK_OPTS: -x -P $GITHUB_WORKSPACE/test

test/COMMON

@@ -1,50 +1,58 @@
-# included by tests scripts
+# shellcheck shell=sh
+# included by test scripts
 
 create_some_files() {
 mkdir -p somefiles/topdir/dir1/dir2/dir3
 
 c=1
-while [ $c -lt 25 ]
+while [ "$c" -lt 25 ]
 do
-   touch somefiles/topdir/dir1/dir2/dir3/$c
-   c=`expr $c + 1`
+   touch "somefiles/topdir/dir1/dir2/dir3/$c"
+   c=$((c + 1))
 done
 
 touch somefiles/read_only_file
 chmod ugo-w somefiles/read_only_file
 }
 
 cmp_substr () {
-  if [ -z "$1" -o -z "$2" ]; then
+  if [ -z "$1" ] || [ -z "$2" ]; then
     return 1
   fi
-  [ -z "${1##*$2*}" ]
+  [ -z "${1##*"$2"*}" ]
   return $?
 }
 
 if test -z "${MESON_BUILD_ROOT}" || test -z "${RMW_FAKE_HOME}"; then
-  echo "This script is used by the build system. Use 'meson test'
-  echo 'from the builddir."
+  echo "This script is used by the build system. Use 'meson test'"
+  echo "from the builddir."
   exit 1
 fi
 
-RMW_FAKE_HOME="${RMW_FAKE_HOME}"/$(basename $0)_dir
-TESTS_DIR="${MESON_SOURCE_ROOT}/test"
+RMW_FAKE_HOME="${RMW_FAKE_HOME}/$(basename "$0")_dir"
+# shellcheck disable=SC2034
 CONFIG="${MESON_SOURCE_ROOT}/test/conf/rmw.testrc"
+# shellcheck disable=SC2034
 ALT_CONFIG="${MESON_SOURCE_ROOT}/test/conf/rmw.alt.testrc"
+# shellcheck disable=SC2034
 PURGE_DISABLED_CONFIG="${MESON_SOURCE_ROOT}/test/conf/rmw.purge_disabled.testrc"
 export BIN_DIR="${MESON_BUILD_ROOT}"
 
 export RMW_FAKE_HOME
 
-if [ -e ${RMW_FAKE_HOME} ]; then
-  rm -rf ${RMW_FAKE_HOME}
+if [ -e "${RMW_FAKE_HOME}" ]; then
+  rm -rf "${RMW_FAKE_HOME}"
 fi
 
+# shellcheck disable=SC2034
 RMW_TEST_CMD_STRING="${BIN_DIR}/rmw -c $CONFIG"
 
-PRIMARY_WASTE_DIR="${RMW_FAKE_HOME}"/.Waste
+# shellcheck disable=SC2034
+PRIMARY_WASTE_DIR="${RMW_FAKE_HOME}/.Waste"
 
+# shellcheck disable=SC2034
 RMW_ALT_TEST_CMD_STRING="${BIN_DIR}/rmw -c ${ALT_CONFIG}"
+# shellcheck disable=SC2034
 RMW_PURGE_DISABLED_CMD="${BIN_DIR}/rmw -c ${PURGE_DISABLED_CONFIG}"
+# shellcheck disable=SC2034
 SEPARATOR="\n\n--- "