Appendix C: Common Regex Patterns - Java Regular Expressions: Taming the java.util.regex Engine

Appendix C: Common Regex Patterns

This appendix presents some practical regex patterns that you can use for common matching and validation tasks.

Table C-1: IP Address *^(([0-1]?\d{1,2}\.)|(2[0-4]\d\.)|(25[0-5]\.)){3} (([0-1]?\d{1,2})|(2[0-4]\d)|(25[0-5]))*$
Regex	Description
^	Beginning of line
(	A group consisting of
(	A subgroup consisting of
[0-1]?	Zero or one, both optional, followed by
\d	Any digit
{1,2}	Repeated one or two times, followed by
\.	A period
)	Close subgroup
\|	Or
(	A subgroup consisting of
2	The digit 2, followed by
[0-4]	Any digit from 0 to 4, followed by
\d	Any digit, followed by
\.	A period
)	Close subgroup
\|	Or
(	A subgroup consisting of
2	The digit 2, followed by
5	The digit 5, followed by
[0-5]	Any digit from 0 to 5, followed by
\.	A period
)	Close subgroup
)	Close group
{3}	Repeated three times, followed by
(	A group consisting of
(	A subgroup consisting of
[0-1]?	Zero or one, both optional, followed by
\d{1,2}	Any two digits
)	Close subgroup
\|	Or
(	A subgroup consisting of
2	The digit 2, followed by
[0-4]	Any digit from 0 to 4, followed by
\d	Any digit
)	Close subgroup
\|	Or
(	A subgroup consisting of
2	The digit 2, followed by
5	The digit 5, followed by
[0-5]	Any digit from 0 to 5, followed by
)	Close subgroup
)	Subgroup
$	End of line
* In English: Three sets of three digits separated by periods, each ranging from 0 to 255, followed by three digits, each ranging from 0 to 255.

Note?/td>

The following pattern also matches the IP address, but all the groups have been marked as noncapturing:

(?:(?:[0-1]?\d{1,2}\.)|(?:2[0-4]\d\.)|(?:25[0-5]\.)){3}(?:(?:[0-1]?\
d{1,2})|(?:2[0-4]\d)|(?:25[0-5]))

This is slightly more efficient than the previous pattern, but it's less legible.

Table C-2: Simple E-mail *^(\p{Alnum}+(\.|\_|\-)?)*\p{Alnum}@(\p{Alnum}+ (\.|\_|\-)?)*\p{Alpha}*$
Regex	Description
^	Beginning of line
(	A group consisting of
\p{Alnum}	A letter or a digit
+	Repeated one or more times, followed by
(	A subgroup consisting of
\.	A period
\|	Or
\_	An underscore
\|	Or
\-	A hyphen
)	Close subgroup
?	The preceding punctuation is optional
)	Close group
*	The previous group can be repeated zero or more times,
?/td>	followed by
\p{Alnum}	A letter or a digit, followed by
@	An @ symbol, followed by
\p{Alnum}	A letter or a digit
+	Repeated one or more times, followed by
(	A group consisting of
\.	A period
\|	Or
\_	An underscore
\|	Or
\-	A hyphen
)	Close group
?	The preceding punctuation is optional
\p{Alpha}	An upper- or lowercase letter
$	End of line
* In English: Any number of alphanumeric characters followed by single hyphens, periods, or underscores, but ending in an alphanumeric character; followed by an @ symbol; followed by any number of alphanumeric characters; followed by single hyphens, periods, or underscores, but ending in an upper- or lowercase character.

Note?/td>

The following pattern matches the previous one exactly, except that it allows an IP address as well:

^(\p{Alnum}+(\.|\_|\-)?)*\p{Alnum}@(((\p{Alnum}+(\.|\_|\-)?)*
\p{Alpha})|((([0-1]?\d{1,2}\.)|(2[0-4]\d\.)|(25[0-5]\.)){3}(([0-1]?\d{1,2})|
(2[0-4]\d)|(25[0-5]))))$

For a breakdown of the IP address pattern, please see Table C-1.

Table C-3: Digit Repeated Exactly n Times *\d{n}*, Where n Is the Number of Digits Needed
Regex	Description
\d	Any number
{n}	Repeated n times
* In English: n digits. Thus, if n was equal to 4, any four digits.

Table C-4: Characters Repeated Exactly n Times *\w{n}*, Where n Is the Number of Characters Needed
Regex	Description
\w	Any number, any digit, or an underscore symbol
{n}	Repeated n times
* In English: n characters. Thus, if n was equal to 4, any four characters.

Table C-5: Characters Repeated n to m Times *\w{n.m}*, Where n Is the Number of Characters Needed
Regex	Description
\w	Any number, any digit, or an underscore symbol
{n	Repeated n times
m}	But not more than m times
* In English: n characters. Thus, if n was equal to 4 and m was equal to 9, any four, five, six, seven, eight, or nine characters.

Table C-6: Credit Cards: Visa, MasterCard, American Express, and Discover *^((4\d{3})|(5[1-5]\d{2})|(6011))-?\d{4}-?\d{4}-?\d{4}|3[4,7]\d{13}*$
Regex	Description
^	Beginning of line
(	A group consisting of
(	A subgroup consisting of
4	the digit four, followed by
\d[3]	Any three digits
)	Close subgroup
\|	Or
(	A subgroup consisting of
5	The digit 5, followed by
[1-5]	Any digit ranging from 1 to 5, followed by
\d[2]	Any two digits
)	Close subgroup
\|	Or
(	A subgroup consisting of
6001	The digits 6, 0, 0, 1
)	Close subgroup, followed by
-?	An optional hyphen, followed by
\d{4]	Any four digits, followed by
-?	An optional hyphen, followed by
\d{4]	Any four digits, followed by
-?	An optional hyphen, followed by
\d{4]	Any four digits, followed by
-?	An optional hyphen
\|	Or
3	The digit 3, followed by
[4,7]	A 4 or a 7, followed by
\d{13]	Any thirteen digits, followed by
$	End of line
* In English: A number starting with 4 and three digits, or 5 and three digits, or 6011, followed by a hyphen, followed by three sets of four digits, or 34 and thirteen digits, or 37 and thirteen digits.

Note?/td>

This regex does not, and cannot, conform to mod 10 verification. To find a Java program that does, please visit http://www.influxs.com.

Table C-7: Real Number *^[+-]?\d+(\.\d+)?*$
Regex	Description
^	Beginning of line, followed by
[+-]?	An optional plus or a minus sign
\d+	Followed by one or more digits, followed by
(	A group consisting of
\.	A period, followed by
\d+	One or more digits
)?	Close group, and make it optional
$	End of line
* In English: Any number of digits followed by an optional decimal component.

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