15일차 # Meta Characters (Metasymbols)

    * POSIX Operators         ==> http://goo.gl/KevzQ

- POSIX Character Class ==> http://goo.gl/OSdcS

ex) [abcdefghijklmnopqrstuvwxyz] ==> [:lower:]

    * PERL-Influenced Extensions to POSIX Standard ==> http://goo.gl/Avm1I

    * Or operator: |

- 'ski|ull' = 'ski' or 'ull'

- 'sk(i|u)ll' = 'skill' or 'skull'

- 'ski|ull|ful' = 'ski' or 'ull' or 'ful'

- '^ski|ull$' = '^ski' or 'ull$'

    * Matching Character List operator: [ ]

- all operators except these are treated as literals:

~ Range operator: -

~ POSIX character class: [: :]

~ POSIX collation element: [. .]

~ POSIX character equivalence class: [= =]

- '[a-d]' = IN ('a', 'b', 'c', 'd')

- '[skill]' = IN ('s', 'k', 'i', 'l')

- '[ski|ull]' = IN ('s', 'k', 'i', '|', 'u', 'l')

- '[[:alpha:]]' = all alphabetic characters

- '[^skill$]' = ???, 아래 NonMatching Character List operator 참조

   * NonMatching Character List operator: [^ ]

- '[^a-d]' = NOT IN ('a', 'b', 'c', 'd')

- '[^skill$]' = NOT IN ('s', 'k', 'i', 'l', '$')

- '[^ski|ull$]' = NOT IN ('s', 'k', 'i', '|', 'u', 'l', '$')

- '[^sk(i|u)ll]'= all except for ...