^ | The pattern has to appear at the beginning of a string. | ^cat matches any string that begins with cat |
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$ | The pattern has to appear at the end of a string. | cat$ matches any string that ends with cat |
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. | Matches any character. | cat. matches catT and cat2 but not catty |
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[] | Bracket expression. Matches one of any characters enclosed. | gr[ae]y matches gray or grey |
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[^] | Negates a bracket expression. Matches one of any characters EXCEPT those enclosed. | 1[^02] matches 13 but not 10 or 12 |
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[-] | Range. Matches any characters within the range. | [1-9] matches any single digit EXCEPT 0 |
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? | Preceeding item must match one or zero times. | colou?r matches color or colour but not colouur |
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+ | Preceeding item must match one or more times. | be+ matches be or bee but not b |
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* | Preceeding item must match zero or more times. | be* matches b or be or beeeeeeeeee |
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() | Parentheses. Creates a substring or item that metacharacters can be applied to | a(bee)?t matches at or abeet but not abet |
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{n} | Bound. Specifies exact number of times for the preceeding item to match. | [0-9]{3} matches any three digits |
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{n,} | Bound. Specifies minimum number of times for the preceeding item to match. | [0-9]{3,} matches any three or more digits |
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{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 |
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| | Alternation. One of the alternatives has to match. | July (first|1st|1) will match July 1st but not July 2 |
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[:alnum:] | alphanumeric character | [[:alnum:]]{3} matches any three letters or numbers, like 7Ds |
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[:alpha:] | alphabetic character, any case | [[:alpha:]]{5} matches five alphabetic characters, any case, like aBcDe |
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[:blank:] | space and tab | [[:blank:]]{3,5} matches any three, four, or five spaces and tabs |
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[:digit:] | digits | [[:digit:]]{3,5} matches any three, four, or five digits, like 3, 05, 489 |
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[:lower:] | lowercase alphabetics | [[:lower:]] matches a but not A |
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[:punct:] | punctuation characters | [[:punct:]] matches ! or . or , but not a or 3 |
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[:space:] | all whitespace characters, including newline and carriage return | [[:space:]] matches any space, tab, newline, or carriage return |
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[:upper:] | uppercase alphabetics | [[:upper:]] matches A but not a |
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// | Default delimiters for pattern | /colou?r/ matches color or colour |
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i | Append to pattern to specify a case insensitive match | /colou?r/i matches COLOR or Colour |
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\b | A word boundary, the spot between word (\w) and non-word (\W) characters | /\bfred\b/i matches Fred but not Alfred or Frederick |
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\B | A non-word boundary | /fred\B/i matches Frederick but not Fred |
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\d | A single digit character | /a\db/i matches a2b but not acb |
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\D | A single non-digit character | /a\Db/i matches aCb but not a2b |
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\n | The newline character. (ASCII 10) | /\n/ matches a newline |
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\r | The carriage return character. (ASCII 13) | /\r/ matches a carriage return |
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\s | A single whitespace character | /a\sb/ matches a b but not ab |
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\S | A single non-whitespace character | /a\Sb/ matches a2b but not a b |
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\t | The tab character. (ASCII 9) | /\t/ matches a tab. |
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\w | A single word character - alphanumeric and underscore | /\w/ matches 1 or _ but not ? |
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\W | A single non-word character | /a\Wb/i matches a!b but not a2b |
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