Regular Expressions (Regex) Reference Sheet
In theoretical computer science and formal language theory, a regular expression (regex or regexp) is a sequence of characters that forms a search pattern, mainly for use in pattern matching with strings, or string matching, i.e. "find and replace"-like operations.
A regular expression is a way for a computer user or programmer to express how a computer program should look for a specified pattern in text and then what the program is to do when each pattern match is found.
Here you can find a Quick Regular Expressions (Regex) Reference Sheet:
Regular Expressions Reference Sheet |
||
| Character | Definition | Example |
| ^ | The pattern has to appear at the beginning of a string. | ^cat matches any string that begins with cat |
| $ | The pattern has to appear at the end of a string. | cat$ matches any string that ends with cat |
| . | Matches any character. | cat. matches catT and cat2 but not catty |
| [] | Bracket expression. Matches one of any characters enclosed. | gr[ae]y matches gray or grey |
| [^] | Negates a bracket expression. Matches one of any characters EXCEPT those enclosed. | 1[^02] matches 13 but not 10 or 12 |
| [-] | Range. Matches any characters within the range. | [1-9] matches any single digit EXCEPT 0 |
| ? | Preceeding item must match one or zero times. | colou?r matches color or colour but not colouur |
| + | Preceeding item must match one or more times. | be+ matches be or bee but not b |
| * | Preceeding item must match zero or more times. | be* matches b or be or beeeeeeeeee |
| () | Parentheses. Creates a substring or item that metacharacters can be applied to | a(bee)?t matches at or abeet but not abet |
| {n} | Bound. Specifies exact number of times for the preceeding item to match. | [0-9]{3} matches any three digits |
| {n,} | Bound. Specifies minimum number of times for the preceeding item to match. | [0-9]{3,} matches any three or more digits |
| {n,m} | Bound. Specifies minimum and maximum number of times for the preceeding item to match. | [0-9]{3,5} matches any three, four, or five digits |
| | | Alternation. One of the alternatives has to match. | July (first|1st|1) will match July 1st but not July 2 |
POSIX Character Classes |
||
| Character | Definition | Example |
| [:alnum:] | alphanumeric character | [[:alnum:]]{3} matches any three letters or numbers, like 7Ds |
| [:alpha:] | alphabetic character, any case | [[:alpha:]]{5} matches five alphabetic characters, any case, like aBcDe |
| [:blank:] | space and tab | [[:blank:]]{3,5} matches any three, four, or five spaces and tabs |
| [:digit:] | digits | [[:digit:]]{3,5} matches any three, four, or five digits, like 3, 05, 489 |
| [:lower:] | lowercase alphabetics | [[:lower:]] matches a but not A |
| [:punct:] | punctuation characters | [[:punct:]] matches ! or . or , but not a or 3 |
| [:space:] | all whitespace characters, including newline and carriage return | [[:space:]] matches any space, tab, newline, or carriage return |
| [:upper:] | uppercase alphabetics | [[:upper:]] matches A but not a |
Perl-Style Metacharacters |
||
| Character | Definition | Example |
| // | Default delimiters for pattern | /colou?r/ matches color or colour |
| i | Append to pattern to specify a case insensitive match | /colou?r/i matches COLOR or Colour |
| \b | A word boundary, the spot between word (\w) and non-word (\W) characters | /\bfred\b/i matches Fred but not Alfred or Frederick |
| \B | A non-word boundary | /fred\B/i matches Frederick but not Fred |
| \d | A single digit character | /a\db/i matches a2b but not acb |
| \D | A single non-digit character | /a\Db/i matches aCb but not a2b |
| \n | The newline character. (ASCII 10) | /\n/ matches a newline |
| \r | The carriage return character. (ASCII 13) | /\r/ matches a carriage return |
| \s | A single whitespace character | /a\sb/ matches a b but not ab |
| \S | A single non-whitespace character | /a\Sb/ matches a2b but not a b |
| \t | The tab character. (ASCII 9) | /\t/ matches a tab. |
| \w | A single word character - alphanumeric and underscore | /\w/ matches 1 or _ but not ? |
| \W | A single non-word character | /a\Wb/i matches a!b but not a2b |
Contents related to 'Regular Expressions (Regex) Reference Sheet'
Reguler Expression (RegEx): A regular expression is a pattern that the regular expression engine attempts to match in input text.