Syntax

	This section is under construction.

Metacharacters

Definitions		Examples
MChar	Definition	Pattern	Sample Matches
^	Start of a string.	^abc	abc, abcdefg, abc123, ...
$	End of a string.	abc$	abc, endsinabc, 123abc, ...
.	Any character (except \n newline)	a.c	abc, aac, acc, adc, aec, ...
\|	Alternation.	bill\|ted	ted, bill
{...}	Explicit quantifier notation.	ab{2}c	abbc
[...]	Explicit set of characters to match.	a[bB]c	abc, aBc
(...)	Logical grouping of part of an expression.	(abc){2}	abcabc
*	0 or more of previous expression.	ab*c	ac, abc, abbc, abbbc, ...
+	1 or more of previous expression.	ab+c	abc, abbc, abbbc, ...
?	0 or 1 of previous expression; also forces minimal matching when an expression might match several strings within a search string.	ab?c	ac, abc
\	Preceding one of the above, it makes it a literal instead of a special character. Preceding a special matching character, see below.	a\sc	a c

Character Escapes

Escaped Char	Description
Ordinary Characters	Characters other than $ . ^ { [ ( \| ) ] } * + ? \ match themselves.
\a	Matches a bell (alarm) \u0007.
\b	Matches a backspace \u0008 if in a [ ]; otherwise matches a word boundary (between \w and \W characters).
\t	Matches a tab \u0009.
\r	Matches a carriage return \u000D.
\v	Matches a vertical tab \u000B.
\f	Matches a form feed \u000C.
\n	Matches a new line \u000A.
\e	Matches an escape \u001B.
\040	Matches an ASCII character as octal (up to three digits); numbers with no leading zero are backreferences if they have only one digit or if they correspond to a capturing group number. For example, the character \040 represents a space.
\x20	Matches an ASCII character using hexadecimal representation (exactly two digits).
\cC	Matches an ASCII control character; for example \cC is control-C.
\u0020	Matches a Unicode character using a hexadecimal representation (exactly four digits).
\*	When followed by a character that is not recognized as an escaped character, matches that character. For example, \* is the same as \x2A.

Character Classes

Char Class	Description
.	Matches any character except \n. If modified by the Singleline option, a period character matches any character.
[aeiou]	Matches any single character included in the specified set of characters.
[^aeiou]	Matches any single character not in the specified set of characters.
[0-9a-fA-F]	Use of a hyphen (–) allows specification of contiguous character ranges.
\p{name}	Matches any character in the named character class specified by {name}. Supported names are Unicode groups and block ranges. For example, Ll, Nd, Z, IsGreek, IsBoxDrawing.
\P{name}	Matches text not included in groups and block ranges specified in {name}.
\w	Matches any word character. Equivalent to the Unicode character categories [\p{Ll}\p{Lu}\p{Lt}\p{Lo}\p{Nd}\p{Pc}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, \w is equivalent to [a-zA-Z_0-9].
\W	Matches any nonword character. Equivalent to the Unicode categories [^\p{Ll}\p{Lu}\p{Lt}\p{Lo}\p{Nd}\p{Pc}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, \W is equivalent to [^a-zA-Z_0-9].
\s	Matches any white-space character. Equivalent to the Unicode character categories [\f\n\r\t\v\x85\p{Z}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, \s is equivalent to [ \f\n\r\t\v].
\S	Matches any non-white-space character. Equivalent to the Unicode character categories [^\f\n\r\t\v\x85\p{Z}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, \S is equivalent to [^ \f\n\r\t\v].
\d	Matches any decimal digit. Equivalent to \p{Nd} for Unicode and [0-9] for non-Unicode, ECMAScript behavior.
\D	Matches any nondigit. Equivalent to \P{Nd} for Unicode and [^0-9] for non-Unicode, ECMAScript behavior.

More Examples

Symbol	Function
[\^$.\|?*+()	Special characters any other will match themselves
\	Escapes special characters and treat as literal
*	Repeat the previous item zero or more times
.	Single character except line break characters
.*	Match zero or more characters
^	Match at the start of a line/string
$	Match at the end of a line/string
.$	Match a single character at the end of line/string
^ $	Match line with a single space
[^A-Z]	Match any line beginning with any char from A to Z

Examples

Samples

Matching specific value from output

Source: pythex.org:

%Cpu(s): 0.3 us, 0.1 sy, 0.0 ni, 99.3 id, 0.2 wa, 0.0 hi, 0.0 si, 0.1 st
%Cpu(s): 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu(s): 0.0 us, 0.0 sy, 0.0 ni,1.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st

Regex:

([0-9]{3}.[0-9]|[0-9]{2}.[0-9]|[0-9].[0-9])(?=\sid)

Explanation:

[0-9]{3} => 3 digits
|        => OR
[0-9]{2} => 2 digits
.        => any character (Dot here)
(?=\sid) => select non-greedy output before 'id' 
?        => non-greedy
\s       => Space
id       => 'id' character

IP Addresses

To Match upto 999.999.999.999:

\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b

OR shortened with a quantifier to:

\b(?:\d{1,3}\.){3}\d{1,3}\b

To match exactly upto 255.255.255.255:

 
\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b

OR shortened with a quantifier to:

\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b

Credit Card numbers

Visa card numbers start with a 4. New cards have 16 digits. Old cards have 13:

^4[0-9]{12}(?:[0-9]{3})?$

MasterCard numbers start with the numbers 51 through 55. All have 16 digits:

^5[1-5][0-9]{14}$

Misc Examples

Match 2 characters/numbers only:

^[0-9a-zA-Z]{2}$

Simple URL Verification:

(http|https):\/\/([a-z])\w+\.(com|net|org)

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