Fix #2909, add a pre-commit hook

.pre-commit-hooks.yaml

@@ -0,0 +1,13 @@
+---
+- id: shellcheck
+  name: ShellCheck v0.9.0
+  description: Static analysis tool for shell scripts
+  language: haskell
+  # https://pre-commit.com/#haskell
+  minimum_pre_commit_version: 3.4.0
+  entry: shellcheck
+  types:
+    - shell
+  # https://github.com/koalaman/shellcheck/issues/809
+  exclude_types:
+    - zsh

README.md

@@ -262,6 +262,17 @@ repos:
 #       args: ["--severity=warning"]  # Optionally only show errors and warnings
 ```
 
+Or (pre-commit version > 3.4.0)
+
+```yaml
+repos:
+-   repo: https://github.com/koalaman/shellcheck
+    rev: v0.7.2
+    hooks:
+    -   id: shellcheck
+#       args: ["--severity=warning"]  # Optionally only show errors and warnings
+```
+
 ### Travis CI
 
 Travis CI has now integrated ShellCheck by default, so you don't need to manually install it.