Git pre-commit hook: Reject commit if a DNS zone file has been changed without changing its SOA serial. The serial needs to be on a separate line that contains ' ; serial'.

pre-commit

#!/bin/bash

# Check if all changed zone files have had their SOA serial incremented.

if git rev-parse --verify HEAD >/dev/null 2>&1
then
	against=HEAD
else
	# Initial commit: diff against an empty tree object
	against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

# Redirect output to stderr.
exec 1>&2

fail=0

while IFS= read -r file
do
    if grep ' ; serial' "$file" > /dev/null && ! (git diff --staged "$file" | grep ' ; serial' > /dev/null)
    then
        echo "SOA serial for zone file '$file' has not been changed!"
        fail=1
    fi
done < <(git diff --cached --name-only --diff-filter=M)

exit $fail