[MISC] Add shellcheck checks to ensure that those few shell scripts w…

…e have are "robust" (bids-standard#1774)

* Add pre-commit definition for shellcheck

* Add "" for a variable use in a test_tag script

* Add github action to shellcheck master on push and PRs

* Skip shellcheck on ci for pre-commit -- needs docker

.github/workflows/shellcheck.yml

@@ -0,0 +1,26 @@
+---
+name: Shellcheck
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+permissions:
+  contents: read
+
+jobs:
+  shellcheck:
+    name: Check shell scripts
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install dependencies
+        run: |
+          sudo apt update && sudo apt install -y shellcheck
+      - name: shellcheck
+        run: |
+          git grep -l '^#\( *shellcheck \|!\(/bin/\|/usr/bin/env \)\(sh\|bash\|dash\|ksh\)\)' | xargs shellcheck

.pre-commit-config.yaml

@@ -1,5 +1,7 @@
 # See https://pre-commit.com for more information
 # See https://pre-commit.com/hooks.html for more hooks
+ci:
+  skip: [shellcheck]
 exclude: 'tools/schemacode/bidsschematools/tests/data/broken_dataset_description.json'
 repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
@@ -71,3 +73,7 @@ repos:
           - types-jsonschema
         args: ["tools/schemacode/bidsschematools"]
         pass_filenames: false
+  - repo: https://github.com/koalaman/shellcheck-precommit
+    rev: v0.9.0
+    hooks:
+      - id: shellcheck

scripts/test_tag

@@ -9,7 +9,7 @@
 EPOCH="$(date +%s)"
 
 GIT_DIR=$( git rev-parse --git-dir )
-REPO_ROOT=$( ls -d ${GIT_DIR%.git} )
+REPO_ROOT=$( ls -d "${GIT_DIR%.git}" )
 
 VERSION_FILE="$REPO_ROOT/src/schema/SCHEMA_VERSION"