Regular Expressions

Simple matches:

Any single character matches itself, unless it is a metacharacter with a special meaning described below. You can cause characters that normally function as metacharacters or escape sequences to be interpreted literally by "escaping" them by preceding them with a backslash "\", for instance: metacharacter "^" match beginning of string, but "\^" match character "^", "\\" match "\" and so on.
foobar- matchs string "foobar"
\^FooBarPtr- matchs "^FooBarPtr"

Escape sequences:

Characters may be specified using a escape sequences syntax much like that used in C and Perl: "\n" matches a newline, "\t" a tab, etc. More generally, "\xnn", where "nn" is a string of hexadecimal digits, matches the character whose ASCII value is nn. If You need wide (Unicode) character code, You can use "\x{nnnn}", where "nnnn" - one or more hexadecimal digits.
foo\x20bar- matchs "foo bar" (note space in the middle)
\tfoobar- matchs "foobar" predefined by tab

Character classes:

You can specify a character class, by enclosing a list of characters in [], which will match any one character from the list. If the first character after the "[" is "^", the class matches any character not in the list. Within a list, the "-" character is used to specify a range, so that a-z represents all characters between "a" and "z", inclusive.
foob[aeiou]r- finds strings "foobar", "foober" etc. but not "foobbr", "foobcr" etc.
foob[^aeiou]r- find strings "foobbr", "foobcr" etc. but not "foobar", "foober" etc.
[-az]- matchs "a", "z" and "-"
[a\-z]- matchs "a", "z" and "-"
[a-z]- matchs all twenty six small characters from "a" to "z"
[\n-\x0D]- matchs any of #10,#11,#12,#13.
[^0-9]- matchs any none digit character

Predefined Classes:

\wan alphanumeric character (including "_")
\Wa nonalphanumeric
\da numeric character
\Da non-numeric
\sany space (same as [ \t\n\r\f])
\Sa non space

Word Boundaries:

\bMatch a word boundary
\BMatch a non-(word boundary)

Iterators:

*zero or more ("greedy"), similar to {0,}
+one or more ("greedy"), similar to {1,}
?zero or one ("greedy"), similar to {0,1}
{n}exactly n times ("greedy")
{n,}at least n times ("greedy")
{n,m}at least n but not more than m times ("greedy")
*?zero or more ("non-greedy"), similar to {0,}?
+?one or more ("non-greedy"), similar to {1,}?
??zero or one ("non-greedy"), similar to {0,1}?
{n}?exactly n times ("non-greedy")
{n,}?at least n times ("non-greedy")
{n,m}?at least n but not more than m times ("non-greedy")

Special Symbols:

|specifies a series of alternatives for a pattern
$nsubexpression n, starts from "1" and "0" is the whole expression

Complex Examples:

More Information:

www.regexpstudio.com
www.regular-expressions.info