\  Marks the next character as either a special character or a literal. For example:

n matches the character n. "\n" matches a
newline character.
 The sequence
\\ matches \ and \( matches ( .

^  Matches the beginning of input. 
$  Matches the end of input. 
*  Matches the preceding character zero or more times. For
example, "zo*" matches either z or zoo.

+  Matches the preceding character one or more times. For
example, "zo+" matches zoo but not z.

?  Matches the preceding character zero or one time. For
example, a?ve? matches the ve in never .

.  Matches any single character except a newline character. 
( subexpression)
 Matches subexpression and remembers the match.
If a part of a regular expression is enclosed in parentheses, that part of the regular expression is grouped together.
Thus a regex operator can be applied to the entire group.
 If you need to use the matched substring within the same regular expression, you can retrieve it
using the backreference (
\num , where num = 1..n ).  If you need to refer the matched substring somewhere outside the current regular expression (for
example, in another regular expression as a replacement string), you can retrieve it using the
dollar sign (
$num , where num = 1..n ).  If you need to include the parentheses characters into a subexpression,
use
\( or \) .

x  y  Matches either x or y. For example, zwood
matches z or wood. (zw)oo matches zoo or wood.

{n }
 n is a nonnegative integer. Matches exactly n
times. For example, o{2} does not match the o in Bob, but
matches the first two o's in foooood.

{n ,}  n is a nonnegative integer. Matches at least n
times.
For example, o{2,} does not match the o in Bob and
matches all the o's in "foooood."
o{1,} is equivalent to o+ . o{0,}
is equivalent to o* .

{
n
,
m
}
 m and n are nonnegative integers. Matches at least n
and at most m times. For example, o{1,3} matches
the first three o's in "fooooood." o{0,1} is equivalent to o? .

[ xyz]  A character set. Matches any one of the enclosed
characters. For example, [abc] matches the a in plain.

[^
xyz
]
 A negative character set. Matches any character not
enclosed. For example, [^abc] matches the p in plain.

[
az
]
 A range of characters. Matches any character in the
specified range. For example, "[az]" matches any lowercase alphabetic
character in the range a through z.

[^
mz
]
 A negative range characters. Matches any character not in
the specified range. For example, [mz] matches any character not in the
range m through z.

\b  Matches a word boundary, that is, the position between a
word and a space. For example, er\b matches the er in never but not
the er in verb.

\B  Matches a nonword boundary. ea*r\B matches the ear in
never early.

\d  Matches a digit character. Equivalent to [09] . 
\D  Matches a nondigit character. Equivalent to [^09] .

\f  Matches a formfeed character. 
\n  Matches a newline character. 
\r  Matches a carriage return character. 
\s  Matches any white space including space, tab, formfeed,
etc. Equivalent to [ \f\n\r\t\v] .

\S  Matches any nonwhite space character. Equivalent to [^ \f\n\r\t\v] .

\t  Matches a tab character. 
\v  Matches a vertical tab character. 
\w  Matches any word character including underscore. Equivalent to [AZaz09_] .

\W  Matches any nonword character. Equivalent to [^AZaz09_] .

\ num  Matches num, where num is a positive integer, denoting a reference back to remembered matches.
For example, (.)\1 matches two consecutive identical characters.

\ n  Matches n, where n is an octal escape value.
Octal escape values should be 1, 2, or 3 digits long.
For example, \11 and
\011 both match a tab character.
\0011 is the equivalent of \001
&1.
Octal escape values should not exceed 256. If they do, only the
first two digits comprise the expression. Allows ASCII codes to be used in
regular expressions.

\x n  Matches n, where n is a hexadecimal escape value. Hexadecimal escape values must
be exactly two digits long.
For example, \x41 matches A .
\x041 is equivalent to \x04 &1 .
Allows ASCII codes to be used in regular expressions.

\\$  Escapes $ . 
\l  Changes the case of the next character to the lower case. 
\u  Changes the case of the next character to the upper case. 
\L  Changes the case of all the subsequent characters up to \E to the lower case. 
\U  Changes the case of all the subsequent characters up to \E to the upper case. 