def regex_findall_variables(content):
    """ extract all variable names from content, which is in format $variable

    Args:
        content (str): string content

    Returns:
        list: variables list extracted from string content

    Examples:
        >>> regex_findall_variables("$variable")
        ["variable"]

        >>> regex_findall_variables("/blog/$postid")
        ["postid"]

        >>> regex_findall_variables("/$var1/$var2")
        ["var1", "var2"]

        >>> regex_findall_variables("abc")
        []

    """
    try:
        vars_list = []
        for var_tuple in variable_regex_compile.findall(content):
            vars_list.append(
                var_tuple[0] or var_tuple[1]
            )
        return vars_list
    except TypeError:
        return []