| Symbol | Meaning |
|---|---|
| . | Any character except newline. |
| . | A period (and so on for \*, \(, \, etc .) |
| ^ | The start of the string. |
| $ | The end of the string. |
| \d,\w,\s | A digit, word character [A-Za-z0-9_], or whitespace. |
| \D,\W,\S | Anything except a digit, word character, or whitespace. |
| [abc] | Character a, b, or c. |
| [a-z] | a through z. |
| [^abc] | Any character except a, b, or c. |
| aa | bb Either aa or bb. |
| ? | Zero or one of the preceding element. |
- | Zero or more of the preceding element.
- | One or more of the preceding element. {n} | Exactly n of the preceding element. {n,} | n or more of the preceding element. {m,n} | Between m and n of the preceding element. ??,*?,+?, {n}?, etc. | Same as above, but as few times as possible. (expr) | Capture expr for use with \1, etc. (?:expr) | Non-capturing group. (?=expr) | Followed by expr. (?!expr) | Not followed by expr. [] | Character set
###Metacharacters
Metacharacter | Meaning | Type ----------- | -------- ---- | --------- \ | Escape next character ^ | Negative a character set
- | Preceding item zero or more times | Repetition Metacharacters
- | Preceding item one or more times | " ? | Preceding item zero or one time | " { | Start quantified repetition of preceding item | Quantified Repetition } | End quantified repetition or preceding item | " ? | Make preceding quntifier lazy ( | Start grouped expression | Grouping Metacharacters ) | End grouped expression | "
###Shorthand Character Sets
| Shorthand | Meaning | Equivalent |
|---|---|---|
| \d | Digit | [0-9] |
| \w | word character | [a-zA-Z0-9_] |
| \s | Whitespace | [ \t\r\n] |
| \D | Not digit | [^0-9] |
| \W | Not word character | [^a-zA-Z0-9_] |
| \S | Not Whitespace | [^ \t\r\n] |
###POSIX Bracket Expressions
| Class | Meaning | Equivalent |
|---|---|---|
| [:alpha:] | Alphabetic Characters | A-Za-z |
| [:digit:] | Numeric Characters | 0-9 |
| [:alnum:] | Alphanumeric Characters | A-Za-z0-9 |
| [:lower:] | Lowercase alphabetic characters | a-z |
| [:upper:] | Uppercase alphabetic characters | A-Z |
| [:punct:] | Punctuation characters | |
| [:space:] | Space characters | \S |
| [:blank:] | Blank characters(space , tab) | |
| [:print:] | Printable characters , spaces | |
| [:graph:] | Printable characters , no spaces | |
| [:cntrl:] | Control Characters(non-printable) | |
| [:xdigit:] | Hexadecimal characters | A-Fa-f0-9 |