.

The dot or period character represents any character (except the new line character).

do. matches:

doe, dog, don, dos, dot

d..r matches:

deer, door

*

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

do* matches:

d, do, doo, dooo, doooo

+

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

do+ matches:

do, doo, dooo, doooo but not d

?

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

do? matches:

d or do but not doo, dooo

( )

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

d(eer)+ matches:

deer or deereer or deereereer

The + sign is applied to the substring within parentheses, so the regular expression 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

The + sign is applied to the set within brackets, so the regular expression 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.

[^ ]

Caret characters within square brackets logically negate the set or range specified, meaning the regular expression 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 “a”

da{2,4} matches:

daa, daaa, daaaa, and daaaa (but not daaaaa)--d followed by 2, 3, or 4 occurrences of a

da{4,} matches:

daaaa, daaaaa, daaaaaa--d followed by 4 or more occurrences of a.

\d

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

\d matches:

1, 12, 123, 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, and others; functionally equivalent to [[:space]]

vegetable\s matches:

"vegetable" followed by any white space character

So the phrase "I like a vegetable in my soup" would trigger the regular expression, but "I like vegetables in my soup" would not.

\S

Any non-white space character; anything other than a space, new line, tab, non-breaking space, and others; 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 regular expression, but "I like a vegetable in my soup" would not.

[:alpha:]

Any alphabetic characters

.REG. [[:alpha:]] matches:

abc, def, xxx, but not 123, @#$.

[:digit:]

Any digit character; functionally equivalent to \d

.REG. [[:digit:]] matches:

1, 12, 123

[: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; 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 regular expression, but "I like vegetables in my soup" would not.

[:graph:]

Any characters except space, control characters, or other similar characters

.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 character (for example, 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:

; : ? ! ~ @ # $ % & * ‘ “ , but not 123, abc

[:lower:]

Any lowercase alphabetic character

.REG. [[:lower:]] matches:

abc, Def, sTress, Do, but not ABC, DEF, STRESS, DO, 123, !@#.

[:upper:]

Any uppercase alphabetic character

.REG. [[:upper:]] matches:

ABC, DEF, STRESS, DO, but not abc, Def, Stress, Do, 123, !@#.

[:xdigit:]

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

.REG. [[:xdigit:]] matches:

0a, 7E, 0f

^

Indicates the beginning of a string

^(notwithstanding) matches:

Any block of text that begins with "notwithstanding"

So the phrase "notwithstanding the fact that I like vegetables in my soup" would trigger the regular expression, 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 ends with "notwithstanding"

So the phrase "notwithstanding the fact that I like vegetables in my soup" would not trigger the regular expression, but "The fact that I like vegetables in my soup notwithstanding" would.

\

Indicates that some characters match a special meaning in a regular expression (for example, +)

.REG. C\/C\+\+ matches:

‘C\C++’

.REG. \* matches:

*

.REG. \? matches:

?

\t

Indicates a tab character (ASCII 0x09 character)

(stress)\t matches:

Any block of text that contained the substring "stress" immediately followed by a tab.

\n

Indicates a new line character (ASCII 0x0A character)

(stress)\n\n matches:

Any block of text that contained the substring "stress" followed immediately by two new line characters.

\r

Indicates a carriage return character (ASCII 0x0D character)

(stress)\r matches:

Any block of text that contained the substring "stress" followed immediately by one carriage return.

\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.

Additional examples that will trigger a match: ~ab12cd and ~Pa3499.

\b

Indicates a backspace character

(stress)\b matches:

Any block of text that contained the substring “stress” followed immediately by one backspace (ASCII 0x08) character