def find_msbuild_unix(filename):
    import os.path
    import sys

    hint_dirs = ['/opt/novell/mono/bin']
    if sys.platform == 'darwin':
        hint_dirs = ['/Library/Frameworks/Mono.framework/Versions/Current/bin', '/usr/local/var/homebrew/linked/mono/bin'] + hint_dirs

    for hint_dir in hint_dirs:
        hint_path = os.path.join(hint_dir, filename)
        if os.path.isfile(hint_path):
            return hint_path
        elif os.path.isfile(hint_path + '.exe'):
            return hint_path + '.exe'

    for hint_dir in os.environ['PATH'].split(os.pathsep):
        hint_dir = hint_dir.strip('"')
        hint_path = os.path.join(hint_dir, filename)
        if os.path.isfile(hint_path) and os.access(hint_path, os.X_OK):
            return hint_path
        if os.path.isfile(hint_path + '.exe') and os.access(hint_path + '.exe', os.X_OK):
            return hint_path + '.exe'

    return None