commit-msg issue checker

#!/bin/sh

# Prevent a commit when no ticket reference is in the message.
# By hooking in just before an actual commit

# To install:
# cd path/to/repo/
# wget --no-clobber https://gist.githubusercontent.com/EmileSonneveld/787b8b51e55027cf848223bc30546dd8/raw -O .git/hooks/commit-msg && chmod +x .git/hooks/commit-msg

check=$(grep -E 'Merge (branch|remote-tracking branch|pull request|tag) ' "$1")
if [ "" != "$check" ]; then
  echo "Not checking ticket reference in merge commit"
  exit 0
fi

echo "Running $0"
# Test the regex here: https://regex101.com/r/J2qFLO/4
check=$(grep -E '((^|[ \n\(])((([a-zA-Z0-9_\-]+\/)?([a-zA-Z0-9_\-]+))?#[0-9]{1,9})|([A-Z]+-[0-9]+)|(https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)))' "$1")
if [ "" = "$check" ]; then
  echo "    Commit message should refer to a ticket!"
  echo ""
  echo "Possible references:"
  echo "    Simple hash with number: #123"
  echo "    Prefix repo: test#123"
  echo "    Prefix organisation/user and repo: test_user-0/test_repo-42#123"
  echo "    GL-... syntax: GL-123"
  echo "    GitLab URL: https://gitlab.com/test_user-0/test_repo-42/-/issues/123"
  echo "    GitHub URL: https://github.com/test_user-0/test_repo-42/issues/123"
  echo "    Jira URL: https://jira.example.com/browse/EP-123"
  echo "    Any URL: https://any-url-actually.org/"
  echo ""
  echo "Blocked:"
  echo "    Double hashtag: ##123 GitHub recognizes this, while it could be unintentional."
  echo ""
  message=$(cat $1)
  echo  "Ignore check with:"
  echo -n "    git commit --no-verify -m \"" && printf "%s" "$message" && echo "\""
  echo ""
  exit 1
else
  echo "    Reference found in commit message."
fi