DRY out hook functionality

Create a utility library to handle argument processing since it is used
by both hooks. Also put the logic for getting unique directory paths
there since it makes sense to put that kind of functionality in a
utility library.

hooks/packer_fmt.sh

@@ -9,30 +9,18 @@ if [ -z "$(command -v packer)" ]; then
   exit 1
 fi
 
-args=()
-files=()
+# The version of readlink on macOS does not support long options
+SCRIPT_DIR="$(dirname "$(readlink -f "$0")")"
+readonly SCRIPT_DIR
+# shellcheck source=lib/util.sh
+source "$SCRIPT_DIR/../lib/util.sh"
 
-while (("$#")); do
-  case "$1" in
-    -*)
-      if [ -f "$1" ]; then
-        files+=("$1")
-      else
-        args+=("$1")
-      fi
-      shift
-      ;;
-    *)
-      files+=("$1")
-      shift
-      ;;
-  esac
-done
+util::parse_cmdline "$@"
 
 error=0
 
-for file in "${files[@]}"; do
-  if ! packer fmt "${args[@]}" -- "$file"; then
+for file in "${FILES[@]}"; do
+  if ! packer fmt "${ARGS[@]}" -- "$file"; then
     error=1
     echo
     echo "Failed path: $file"

hooks/packer_validate.sh

@@ -9,40 +9,20 @@ if [ -z "$(command -v packer)" ]; then
   exit 1
 fi
 
-args=()
-files=()
-
-while (("$#")); do
-  case "$1" in
-    -*)
-      if [ -f "$1" ]; then
-        files+=("$1")
-      else
-        args+=("$1")
-      fi
-      shift
-      ;;
-    *)
-      files+=("$1")
-      shift
-      ;;
-  esac
-done
+# The version of readlink on macOS does not support long options
+SCRIPT_DIR="$(dirname "$(readlink -f "$0")")"
+readonly SCRIPT_DIR
+# shellcheck source=lib/util.sh
+source "$SCRIPT_DIR/../lib/util.sh"
 
-paths=()
-index=0
-for file in "${files[@]}"; do
-  paths[index]=$(dirname -- "$file")
-  ((++index))
-done
+util::parse_cmdline "$@"
 
-unique_paths=()
-while IFS='' read -r line; do unique_paths+=("$line"); done < <(printf '%s\n' "${paths[@]}" | sort --unique)
+util::get_unique_directory_paths "${FILES[@]}"
 
 error=0
 
-for path in "${unique_paths[@]}"; do
-  if ! packer validate "${args[@]}" -- "$path"; then
+for path in "${UNIQUE_PATHS[@]}"; do
+  if ! packer validate "${ARGS[@]}" -- "$path"; then
     error=1
     echo
     echo "Failed path: $path"

lib/util.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+
+set -o nounset
+set -o errexit
+set -o pipefail
+
+#######################################
+# Process the command line and separate arguments from files
+# Globals:
+#   ARGS
+#   FILES
+#######################################
+function util::parse_cmdline() {
+  # Global variable arrays
+  ARGS=()
+  FILES=()
+
+  while (("$#")); do
+    case "$1" in
+      -*)
+        if [ -f "$1" ]; then
+          FILES+=("$1")
+        else
+          ARGS+=("$1")
+        fi
+        shift
+        ;;
+      *)
+        FILES+=("$1")
+        shift
+        ;;
+    esac
+  done
+}
+
+#######################################
+# Create a list of unique directory paths from a list of file paths
+# Globals:
+#   UNIQUE_PATHS
+#######################################
+function util::get_unique_directory_paths() {
+  # Global variable arrays
+  UNIQUE_PATHS=()
+
+  local -a paths
+
+  index=0
+  for file in "$@"; do
+    paths[index]=$(dirname -- "$file")
+    ((++index))
+  done
+
+  UNIQUE_PATHS=()
+  while IFS='' read -r line; do UNIQUE_PATHS+=("$line"); done < <(printf '%s\n' "${paths[@]}" | sort --unique)
+}