Add ShellCheck linting workflow

This commit adds GitHub Actions workflow for ShellCheck to lint bash scripts:

- Created .github/workflows/shellcheck.yml
- Runs on all pull requests and pushes
- Uses ubuntu-latest where ShellCheck is pre-installed
- Finds and lints all *.sh files in the repository

Additionally, this commit fixes ShellCheck warnings in existing scripts:

- scripts/release-notes.sh: Fixed unquoted variables, replaced expr with 0
- scripts/util.sh: Replaced backticks with $(...), fixed trap command quoting
- scripts/validate-license.sh: Used mapfile for array assignment instead of command substitution

All bash scripts now pass ShellCheck validation.

Fixes: #31689
Signed-off-by: Adesh Deshmukh <adeshkd123@gmail.com>

.github/workflows/shellcheck.yml

@@ -0,0 +1,20 @@
+name: ShellCheck
+
+on:
+  push:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  shellcheck:
+    name: ShellCheck
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # pin@v6.0.2
+      - name: Run ShellCheck
+        run: |
+          shellcheck --version
+          find . -type f -name "*.sh" -not -path "./vendor/*" -not -path "./.git/*" | xargs shellcheck

scripts/release-notes.sh

@@ -29,10 +29,10 @@ if [[ -z "${PREVIOUS_RELEASE}" || -z "${RELEASE}" ]]; then
 fi
 
 ## validate git tags
-for tag in $RELEASE $PREVIOUS_RELEASE; do
-  OK=$(git tag -l ${tag} | wc -l)
+for tag in "$RELEASE" "$PREVIOUS_RELEASE"; do
+  OK=$(git tag -l "$tag" | wc -l)
   if [[ "$OK" == "0" ]]; then
-    echo ${tag} is not a valid release version
+    echo "$tag is not a valid release version"
     exit 1
   fi
 done
@@ -46,20 +46,20 @@ if [[ ! -e "./_dist/helm-${RELEASE}-darwin-amd64.tar.gz.sha256sum" ]]; then
 fi
 
 ## Generate CHANGELOG from git log
-CHANGELOG=$(git log --no-merges --pretty=format:'- %s %H (%aN)' ${PREVIOUS_RELEASE}..${RELEASE})
-if [[ ! $? -eq 0 ]]; then
+CHANGELOG=$(git log --no-merges --pretty=format:'- %s %H (%aN)' "${PREVIOUS_RELEASE}".."${RELEASE}")
+if ! git log --no-merges --pretty=format:'- %s %H (%aN)' "${PREVIOUS_RELEASE}".."${RELEASE}" > /dev/null; then
   echo "Error creating changelog"
   echo "try running \`git log --no-merges --pretty=format:'- %s %H (%aN)' ${PREVIOUS_RELEASE}..${RELEASE}\`"
   exit 1
 fi
 
 ## guess at MAJOR / MINOR / PATCH versions
-MAJOR=$(echo ${RELEASE} | sed 's/^v//' | cut -f1 -d.)
-MINOR=$(echo ${RELEASE} | sed 's/^v//' | cut -f2 -d.)
-PATCH=$(echo ${RELEASE} | sed 's/^v//' | cut -f3 -d.)
+MAJOR=$(echo "${RELEASE}" | sed 's/^v//' | cut -f1 -d.)
+MINOR=$(echo "${RELEASE}" | sed 's/^v//' | cut -f2 -d.)
+PATCH=$(echo "${RELEASE}" | sed 's/^v//' | cut -f3 -d.)
 
 ## Print release notes to stdout
-cat <<EOF
+cat <<'EOF'
 ## ${RELEASE}
 
 Helm ${RELEASE} is a feature release. This release, we focused on <insert focal point>. Users are encouraged to upgrade for the best experience.
@@ -98,8 +98,8 @@ The [Quickstart Guide](https://helm.sh/docs/intro/quickstart/) will get you goin
 
 ## What's Next
 
-- ${MAJOR}.${MINOR}.$(expr ${PATCH} + 1) will contain only bug fixes.
-- ${MAJOR}.$(expr ${MINOR} + 1).${PATCH} is the next feature release. This release will focus on ...
+- ${MAJOR}.${MINOR}.$((${PATCH} + 1)) will contain only bug fixes.
+- ${MAJOR}.$((${MINOR} + 1)).${PATCH} is the next feature release. This release will focus on ...
 
 ## Changelog
 

scripts/util.sh

@@ -28,7 +28,7 @@ kube::util::trap_add() {
     local new_cmd
 
     # Grab the currently defined trap commands for this trap
-    existing_cmd=`trap -p "${trap_add_name}" |  awk -F"'" '{print $2}'`
+    existing_cmd=$(trap -p "${trap_add_name}" |  awk -F"'" '{print $2}')
 
     if [[ -z "${existing_cmd}" ]]; then
       new_cmd="${trap_add_cmd}"

scripts/validate-license.sh

@@ -28,7 +28,7 @@ find_files() {
 }
 
 # Use "|| :" to ignore the error code when grep returns empty
-failed_license_header=($(find_files | xargs grep -L 'Licensed under the Apache License, Version 2.0 (the "License")' || :))
+mapfile -t failed_license_header < <(find_files | xargs grep -L 'Licensed under the Apache License, Version 2.0 (the "License")' || :)
 if (( ${#failed_license_header[@]} > 0 )); then
   echo "Some source files are missing license headers."
   printf '%s\n' "${failed_license_header[@]}"
@@ -36,7 +36,7 @@ if (( ${#failed_license_header[@]} > 0 )); then
 fi
 
 # Use "|| :" to ignore the error code when grep returns empty
-failed_copyright_header=($(find_files | xargs grep -L 'Copyright The Helm Authors.' || :))
+mapfile -t failed_copyright_header < <(find_files | xargs grep -L 'Copyright The Helm Authors.' || :)
 if (( ${#failed_copyright_header[@]} > 0 )); then
   echo "Some source files are missing the copyright header."
   printf '%s\n' "${failed_copyright_header[@]}"