Grep

    grep smug files         {search files for lines with 'smug'}
    grep '^smug' files      {'smug' at the start of a line}
    grep 'smug$' files      {'smug' at the end of a line}
    grep '^smug$' files     {lines containing only 'smug'}
    grep '\^s' files        {lines starting with '^s', "\" escapes the ^}
    grep '[Ss]mug' files    {search for 'Smug' or 'smug'}
    grep 'B[oO][bB]' files  {search for BOB, Bob, BOb or BoB }
    grep '^$' files         {search for blank lines}
    grep '[0-9][0-9]' file  {search for pairs of numeric digits}

http://www.robelle.com/smugbook/regexpr4.txt