]$ - matches a line containing one a or one b
]c) - matches 'ac' or 'bc'
]c)|b - matches 'ac', 'bc' or 'b'
]- matches any single numeral
]- matches a single lower case alphal character
]- matches any single alphabetical character
Always remember that, if you are in doubt of the ordering in which the regular expression is evaluated,insert brackets.