post-commit:

#!/usr/bin/ruby

lastlog = `git log -1`
raise "Error in git log -1" if $?.exitstatus != 0
if lastlog.include?("fix") and not lastlog.include?("closebug")
  `echo bug >> bug`
  raise "Error in echo" if $?.exitstatus != 0
  `git add bug`
  raise "Error in git add bug" if $?.exitstatus != 0
  `git commit -m closebug`
  raise "Error in git commit -m closebug" if $?.exitstatus != 0
end

--- end of post-commit

mkdir test;
cd test;
git init;
chmod 755 ../post-commit;
cp ../post-commit .git/hooks/post-commit;

echo foo >> foo
git add foo
git commit -m 'foo'

echo foo >> foo
git add foo
git commit -m 'fix foo'
git status
# On branch master
#nothing to commit (working directory clean)


echo foo >> foo
git commit -a -m 'fix foo'
git status
# On branch master
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#
#	modified:   bug
#
#no changes added to commit (use "git add" and/or "git commit -a")

git --version
#git version 1.5.3.2