Bash shell regular expression

브라켓 expression

POSIX Bracket Expressions

POSIX bracket expressions are a special kind of character classes. POSIX bracket expressions match one character out of a set of characters, just like regular character classes.

Standard POSIX

[[:alnum:]]   Alphanumeric characters
[[:alpha:]]   Alphabetic characters
[[:blank:]]   Space and tab
[[:cntrl:]]   Control characters
[[:digit:]]   Digits
[[:graph:]]   Visible characters (anything except spaces and control characters)
[[:lower:]]   Lowercase letters
[[:print:]]   Visible characters and spaces (anything except control characters)
[[:punct:]]   Punctuation (and symbols).
[[:space:]]   All whitespace characters, including line breaks
[[:upper:]]   Uppercase letters
[[:xdigit:]]  Hexadecimal digits

None Standards
[[:ascii:]]   ASCII characters
[[:word:]]    Word characters (letters, numbers and underscores)

legacy syntax (can someone find reference to these?)
[[:<:]]       Start of Word 
[[:>:]]       End of Word