Counting and Grouping

Element

What it means

Example

.

The dot or period character rep­resents any character except new line character.

do. matches doe, dog, don, dos, dot, etc.d.r matches deer, door, etc.

*

The asterisk character means zero or more instances of the preceding element.

do* matches d, do, doo, dooo, doooo, etc.

+

The plus sign character means one or more instances of the pre­ceding element.

do+ matches do, doo, dooo, doooo, etc. but not d

?

The question mark character means zero or one instances of the preceding element.

do?g matches dg or dog but not doog, dooog, etc.

( )

Parenthesis characters group whatever is between them to be considered as a single entity.

d(eer)+ matches deer or deer­eer or deereereer, etc. The + sign is applied to the substring within parentheses, so the regex looks for d followed by one or more of the grouping "eer." 

[ ]

Square bracket characters indi­cate a set or a range of charac­ters.

d[aeiouy]+ matches da, de, di, do, du, dy, daa, dae, dai, etc. The + sign is applied to the set within brackets parentheses, so the regex looks for d fol­lowed by one or more of any of the characters in the set [aeioy].

d[A-Z] matches dA, dB, dC, and so on up to dZ. The set in square brackets represents the range of all upper-case letters between A and Z.

^

Carat characters within square brackets logically negate the set or range specified, meaning the regex will match any character that is not in the set or range.

d[^aeiouy] matches db, dc or dd, d9, d#. d followed by any single character except a vowel.

{ }

Curly brace characters set a spe­cific number of occurrences of the preceding element. A single value inside the braces means that only that many occurrences will match. A pair of numbers separated by a comma repre­sents a set of valid counts of the preceding character. A single digit followed by a comma means there is no upper bound.

da{3} matches daaa. d fol­lowed by 3 and only 3 occur­rences of ”r;a”. da{2,4} matches daa, daaa, daaaa, and daaaa (but not daaaaa). d followed by 2, 3, or 4 occur­rences of ”r;a”. da{4,} matches daaaa, daaaaa, daaaaaa, etc. d followed by 4 or more occur­rences of ”r;a”.

Character Classes (shorthand)

Example

What it means

Example

\d

Any digit character; functionally equivalent to [0-9] or [[:digit:]]

\d matches 1, 12, 123, etc., but not 1b7. One or more of any digit characters.

\D

Any non-digit character; func­tionally equivalent to [^0-9] or [^[:digit:]]

\D matches a, ab, ab&, but not 1. One or more of any charac­ter but 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9.

\w

Any "word" character. That is, any alphanumeric character; functionally equivalent to [_A-Za-z0-9] or [_[:alnum:]]

\w matches a, ab, a1, but not !&. One or more upper- or lower-case letters or digits, but not punctuation or other spe­cial characters.

\W

Any non-alphanumeric charac­ter; functionally equivalent to [^_A-Za-z0-9] or [^_[:alnum:]]

\W matches *, &, but not ace or a1. One or more of any charac­ter but upper- or lower-case letters and digits.

\s

Any white space character; space, new line, tab, non-break­ing space, etc.; functionally equivalent to [[:space]]

vegetable\s matches "vegeta­ble" followed by any non-white space character. So the phrase "I like vegetables in my soup" would trigger the regex, but "I like a vegetable in my soup" would not.

\S

Any non-white space character; anything other than a space, new line, tab, non-breaking space, etc.; functionally equiva­lent to [^[:space]]

vegetable\S matches "vegeta­ble" followed by any non-white space character. So the phrase "I like vegetables in my soup" would trigger the regex, but "I like a vegetable in my soup" would not.

Character classes

Element

What it means

Example

[:alpha:]

Any alphabetic characters

.REG. [[:alpha:]] matches abc, def, xxx, but not 123 or @#$.

[:digit:]

Any digit character; functionally equivalent to  \d

.REG. [[:digit:]] matches 1, 12, 123, etc.

[:alnum:]

Any "word" character. That is, any alphanumeric character; functionally equivalent to \w

.REG. [[:alnum:]] matches abc, 123, but not ~!@.

[:space:]

Any white space character; space, new line, tab, non-breaking space, etc.; func­tionally equivalent to \s

.REG. (vegetable)[[:space:]] matches "vegetable" followed by any white space character. So the phrase "I like a vegeta­ble in my soup" would trigger the regex, but "I like vegeta­bles in my soup" would not.

[:graph:]

Any characters except space, control characters or the like

.REG. [[:graph:]] matches 123, abc, xxx, ><”, but not space or control characters.

[:print:]

Any characters (similar with [:graph:]) but includes the space character

.REG. [[:print:]] matches 123, abc, xxx, ><”, and space char­acters.

[:cntrl:]

Any control characters (e.g. CTRL + C, CTRL + X)

.REG. [[:cntrl:]] matches 0x03, 0x08, but not abc, 123, !@#.

[:blank:]

Space and tab characters

.REG. [[:blank:]] matches space and tab characters, but not 123, abc, !@#

[:punct:]

Punctuation characters

.REG. [[:punct:]] matches ; : ? ! ~ @ # $ % & * ’r; ”r; , etc., but not 123, abc

[:lower:]

Any lowercase alphabetic char­acters (Note : ’r;Enable case sensitive matching’ must be enabled or else it will function as [:alnum:])

.REG. [[:lower:]] matches abc, Def, sTress, Do, etc., but not ABC, DEF, STRESS, DO, 123, !@#.

[:upper:]

Any uppercase alphabetic characters (Note : ’r;Enable case sensitive matching’ must be enabled or else it will func­tion as [:alnum:])

.REG. [[:upper:]] matches ABC, DEF, STRESS, DO, Def, Stress, Do, etc., but not abc, 123, !@#.

[:xdigit:]

Digits allowed in a hexadecimal number (0-9a-fA-F)

.REG. [[:xdigit:]] matches 0a, 7E, 0f, etc.

Pattern anchor regular expressions

Element

What it means

Example

^

Indicates the beginning of a string.

^

(notwithstanding) matches any block of text that began with "notwithstanding" So the phrase "notwithstanding the fact that I like vegetables in my soup" would trigger the regex, but "The fact that I like vegeta­bles in my soup notwithstand­ing" would not.

$

Indicates the end of a string.

(notwithstanding) $ matches any block of text that ended with "notwithstanding" So the phrase "notwithstanding the fact that I like vegetables in my soup" would not trigger the regex, but "The fact that I like vegetables in my soup notwith­standing" would.

Escape sequences regular expressions

Element

What it means

Example

\

In order to match some charac­ters that have special meaning in regular expression (for exam­ple, "+").

(1) .REG. C\\C\+\+ matches ’r;C\C++’.

(2) .REG. \* matches *.

(3) .REG. \? matches ?.

\t

Indicates a tab character.

(stress) \t matches any block of text that contained the sub­string "stress" immediately fol­lowed by a tab (ASCII 0x09) character.

\n

Indicates a new line character.

Note: Different platforms repre­sent a new line character. On Windows, a new line is a pair of characters, a carriage return fol­lowed by a line feed. On Unix and Linux, a new line is just a line feed, and on Macintosh a new line is just a carriage return.

(stress) \n matches any block of text that contained the sub­string "stress" followed immedi­ately by two new line (ASCII 0x0A) characters.

\r

Indicates a carriage return char­acter.

(stress) \r matches any block of text that contained the sub­string "stress" followed immedi­ately by one carriage return (ASCII 0x0D) character.

\b

Indicates a backspace character

(stress) \b matches any block of text that contained the sub­string ”r;stress” followed imme­diately by one backspace (ASCII 0x08) character.

\xhh

Indicates an ASCII character with given hexadecimal code (where hh represents any two-digit hex value).

\x7E(\w){6} matches any block of text containing a "word" of exactly six alphanumeric char­acters preceded with a ~ (tilde) character. So, the words ’r;~ab12cd’, ’r;~Pa3499’ would be matched, but ’r;~oops’ would not.