Basic Regular Expressions

.

Matches any characters except a newline.

^

Matches the start of the string or line.

$

Matches the end of the string or just before the newline at the end of the string.

*

Matches the previous element zero or more times. For example, "ab*" can match "a", "ab", and "abb".

+

Matches the previous element one or more times. For example, "be+" can match "been" and "bent".

?

Matches the previous element zero or one time. For example, "ab?" can match "a" and "ab".

*?

Matches the previous element zero or more times, but as few times as possible. For example, "\d*?\.\d" can match "0", "19.9", and "219.6".

+?

Matches the previous element one or more times, but as few times as possible. For example, "se+?" can match "see" and "sea".

??

Matches the previous element zero or one time, but as few times as possible. For example, "rai??n" can match "ran" and "rain".

[]

A bracket expression. Matches a single character that is contained within the brackets. For example, [amk] will match "a", "m", or "k".

[a-z] specifies a range which matches any lowercase letter from "a" to "z". These forms can be mixed: [abcx-z] matches "a", "b", "c", "x", "y", or "z", as does [a-cx-z].

[0-5][0-9] will match all two-digit numbers from 00 to 59.

The - character is treated as a literal character if it is the last or the first character within the brackets. For example, [abc-] and [-abc]. But the backslash escapes are not allowed.

|

Matches any one element separated by the vertical bar (|) character.

( )

Defines a marked sub-expression. The string matched within the parentheses can be recalled later. A marked sub-expression is also called a block or capturing group.

\s

Matches any whitespace characters. It is equivalent to the [\t\n\r\f\v] set.

\d

Matches any decimal digits. It is equivalent to the [0-9] set.

\w

Matches any alphanumeric characters and the underscore. It is equivalent to the [a-zA-Z0-9_] set.