Regular Expressions (Regex) Reference Sheet
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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
added 11 years 8 months ago
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.