This morning I had to program some regular expressions. As usual, I found myself Googling for some help. I used to have a nice cheat sheet for regular expressions, but I appear to have lost it. Let's create another one.
Examples
| Name | Pattern | Description |
|---|
| Integer | \d+ | Match a sequence of digits (must have at least 1) |
| Real Number | \d*(.\d*)? | Allows numbers before and after the decimal point (cannot end with a decimal though) |
| Hexadecimal | [0-9a-f]+ | Hexdecimal digits (0-9 or a-f) |
| Date | \d{4}-\d{2}-\d{2} | Date in "yyyy-mm-dd" format |
Character Expressions
| Characters | Descriptions |
|---|
[abc] | Find one character from the options between the brackets |
[^abc] | Find one character NOT between the brackets |
[0-9] | Find one character in the range 0 to 9 |
Character Shortcuts
| Shortcut | Equivalent | Description |
|---|
. | [^\n] | Any character (except a line break) |
\d | [0-9] | Digit (0-9) |
\s | [ \t\n\r\v] | Whitespace (space, tab, newline, carriage return, vertical tab) |
\w | [a-zA-Z0-9_] | "Word" character (typically: ascii letter, digit, or underscore) |
Escaped Characters
Use "\" to escape the following special characters: .*+?$^/[{()}]\
Groups
| Group | Description | Example | Example Match |
|---|
\| | "OR": match one of the terms | 22\|33\|44 | 33 |
(...) | Capturing group. This can be used to return a specific part of the text or to reference it later | A(nt\|pple) | Apple (capturing "pple") |
(?...) | Non-capturing group. | A(?:nt\|pple) | Apple (nothing captured) |
\1 | Contents of group 1 | r(\w)g\1x | regex |
\2 | Contents of group 2 | (\d\d)\+(\d\d)=\2\+\1 | 12+65=65+12 |
Repetitions
| Symbol | Description |
|---|
? | Once or none |
* | Zero or more times |
+ | One or more times |
{3} | Exactly 3 times |
{2,4} | 2-4 times |
{3,} | 3 or more times |
Anchors and Boundaries
| Symbol | Description |
|---|
^ | Start of text |
$ | End of text |
References
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