Regular expressions are widely used for example in XML schema and Linux commands such as sed and awk. |
|
Syntax |
Description |
|---|---|
| ^ | Indicates the beginning of a tring - e.g. ^a will only match 'a' at the beginning of a string |
| & | Indicates the end of a tring - e.g. a$ will only match 'a' at the end of a string |
| . | Matches a single character |
| + | Matches one or more instances |
| * | Matches zero or more instances |
| ? | Matches zero or one instances |
| {n} | Matches n instances |
| {n,} | Matches n or more instances |
| {n,m} | Matches between n and m instances |
| (ab) | Brackets group a sequence of letters - e.g. (ab)+ for "ababab" |
| a(b|c) | | indicates a choice - e.g. "ab" or "ac" |
| [abc] | Indicates a set of allowed choices |
| [^abc] | Indicates a set of disallowed choices |
| [a-z] | Indicates a set as a range of characters |
| \ | Escapes one of the above special characters - e.g. \* will indicates a literal asterisk |
| \w | Matches any word character (equivalent to [a-zA-Z_]) |
| \s | Matches any whitespace character (tabs and spaces) |
| \d | Matches any digit (equivalent to [0-9]) |
| \l | Matches any lower case letter (equivalent to [a-z]) |
| \u | Matches any upper case letter (equivalent to [A-Z]) |
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