terraform-fmt updates files, optionally skipped via flags

README.md

@@ -127,6 +127,21 @@ Now when the pre-commit hook runs, it will call `helm lint` with both `linter_va
 helm lint -f values.yaml -f linter_values.yaml .
 ```
 
+## terraform-fmt arguments
+
+By default, `terraform-fmt` will write changes back to the original file.
+You can skip this by setting the `--no-autofix` flag.
+
+```yaml
+repos:
+  - repo: https://github.com/gruntwork-io/pre-commit
+    rev: <VERSION>
+    hooks:
+      - id: terraform-fmt
+        args: ["--no-autofix"]
+```
+
+
 ## Shellcheck Arguments
 
 To enable optional shellcheck features you can use the `--enable` flag.

hooks/terraform-fmt.sh

@@ -7,11 +7,43 @@ set -e
 # workaround to allow GitHub Desktop to work, add this (hopefully harmless) setting here.
 export PATH=$PATH:/usr/local/bin
 
+write_changes=true
+FILES=()
+
+parse_arguments() {
+	while (($# > 0)); do
+		# Grab param and value splitting on " " or "=" with parameter expansion
+		local PARAMETER="${1%[ =]*}"
+		local VALUE="${1#*[ =]}"
+		if [[ "$PARAMETER" == "$VALUE" ]]; then VALUE="$2"; fi
+		shift
+		case "$PARAMETER" in
+		--no-autofix)
+			write_changes=false
+			;;
+		-*)
+			echo "Error: Unknown option: $PARAMETER" >&2
+			exit 1
+			;;
+		*)
+			FILES+=("$PARAMETER")
+			;;
+		esac
+	done
+}
+
+parse_arguments "$@"
+
 # Store and return last failure from fmt so this can validate every directory passed before exiting
 FMT_ERROR=0
 
-for file in "$@"; do
-  terraform fmt -diff -check "$file" || FMT_ERROR=$?
+for file in "$FILES"; do
+  file=$(dirname "$file")
+  if [ "$write_changes" = true ]; then
+    terraform fmt "$file" || FMT_ERROR=$?
+  else
+    terraform fmt -diff -check "$file" || FMT_ERROR=$?
+  fi
 done
 
 exit ${FMT_ERROR}