Regular Expressions Special Symbols

• [:alnum:]  Represents English uppercase and lowercase letters and numbers, and 0-9, A-Z, a-z.
• [:alpha:]  Represents any English uppercase and lowercase letters, as well as A-Z, a-z.
• [:blank:]  Represents both the space key and the [Tab] key.
• [:cntrl:]  Represents the control keys on the keyboard, including CR, LF, Tab, Del... etc.
• [:digit:]  Represents only numbers, that is, 0-9.
• [:graph:]  All keys except blank characters (space key and [Tab] key).
• [:lower:]  Represents lowercase characters, i.e. a-z.
• [:print:]  Represents any character that can be printed.
  
• [:punct:]  Represents punctuation symbol, that is: "'?!;: # $...
  
• [:upper:]  Represents uppercase characters, which is A-Z.
  
• [:space:]  Any characters that will produce blanks, including blank keys, [Tab], CR, etc.
  
• [:xdigit:]  Represents a hexadecimal number type, so it includes: 0-9, A-F, a-f numbers and characters.