fix: Use regular grep for copyright check

Author: aiven-anton

.pre-commit-config.yaml

@@ -17,10 +17,8 @@ repos:
     name: copyright
     language: system
     types: [ python ]
-    pass_filenames: false
-    # Lists the Python files that do not have an Aiven copyright. Exits with a
-    # non-zero exit code if any are found.
-    entry: bash -c "! git grep -ELm1 'Copyright \(c\) 20[0-9]{2} Aiven' -- '*.py' ':!*__init__.py'"
+    exclude: __init__\.py
+    entry: ./copyright.sh
 
 - repo: https://github.com/shellcheck-py/shellcheck-py
   rev: v0.9.0.2

copyright.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+missing_copyright=$(
+    grep \
+        --extended-regexp \
+        --files-without-match \
+        --max-count=1 \
+        'Copyright \(c\) 20[0-9]{2} Aiven' \
+        -- "$@"
+)
+
+if [[ -n $missing_copyright ]]; then
+    echo "💥 There are files missing required copyright statement."
+    echo "$missing_copyright"
+    exit 1
+else
+    echo "✅ All files have required copyright statement."
+fi