| Character Class | Description |
|---|---|
[:alnum:] |
The alphanumeric characters. In ASCII, equivalent to: [A-Za-z0-9]. |
[:word:] |
The same as [:alnum:], with the addition of the underscore (_) character. |
[:blank:] |
The space and tab characters. |
[:digit:] |
The numerals 0 through 9. |
[:lower:] |
The lowercase letters. |
[:print:] |
The printable characters. All the characters in [:graph:] plus the space character. |
[:upper:] |
The uppercase characters. |
[:alpha:] |
The alphabetic characters. In ASCII, equivalent to: [A-Za-z]. |
[:cntrl:] |
The ASCII control codes. Includes the ASCII characters 0 through 31 and 127. |
[:graph:] |
The visible characters. In ASCII, it includes characters 33 through 126. |
[:punct:] |
The punctuation characters. In ASCII, equivalent to: [-!"#$%&'()*+,./:;<=>?@[\\\]_`{|}~]. |
[:space:] |
The whitespace characters including space, tab, carriage return, newline, vertical tab, and form feed. In ASCII, equivalent to: [ \t\r\n\v\f]. |
[:xdigit:] |
Characters used to express hexadecimal numbers. In ASCII, equiv- alent to: [0-9A-Fa-f]. |
Quantifiers are ways to specify the number of times an element is matched.
| Specifier | Meaning |
|---|---|
? |
Match the preceding element zero or one time. |
* |
Match the preceding element zero or more times. |
+ |
Match the preceding element one or more times |
{n} |
Match the preceding element if it occurs exactly n times. |
{n,m} |
Match the preceding element if it occurs at least n times but no more than m times. |
{n,} |
Match the preceding element if it occurs n or more times. |
{,m} |
Match the preceding element if it occurs no more than m times. |