Regular Expression

Javascript based regular expression engine.

http://regexpal.com/ - save it to file and enable global checkmark which is enabled by default.

Python reqular expression test

http://pythex.org/

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grep

egrep = grep -e

awk, vi, emacs

POSIX

BRE - Basic R.E.

ERE - Extended R.E.

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\ : excape character

\t : tab

\r, \n, \r\n : new lines

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[aeiou] : any of vowel

[0-9] : - is range character

[A-Za-z] : all alphabet

[^aeiou] : non vowel

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[\d\s] : digit and space

[^\d\s] : non digit and non space

[\D\S] : all ==> don't use multiple capital characters

*POSIX expressions are not popular

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#Year

(19|20)\d\d

/(19[5-9]\d|20[0-4]\d)/

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# Does first letter have to be capitalized?

Regex:  /^[A-Z][A-Za-z]+$/m

# Capture first, middle, and last name

Regex:  /^([A-Z][A-Za-z.'\-]+) (?:([A-Z][A-Za-z.'\-]+) )?([A-Z][A-Za-z.'\-]+)$/m

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# U.S. postal codes

Regex:  /^\d{5}(-\d{4})?$/m

# Canada postal codes

Regex:  /^[A-Z]\d[A-Z] \d[A-Z]\d$/m

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# Email and domain specifications allow other characters

Regex:  /^[\w.%+\-]+@[\w.\-]+\.[A-Za-z]{2,3}$/

Regex:  /^[\w.%+\-]+@[\w.\-]+\.[A-Za-z]{2,6}$/

String: "someone@somewhere.museum"

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# Query string portion

Regex:  /^(http|https):\/\/[\w\-_]+(\.[\w\-_]+)+.*$/

Regex:  /^(http|https):\/\/[\w\-_]+(\.[\w\-_]+)+[/?#]?.*$/

Regex:  /^(http|https):\/\/[\w\-_]+(\.[\w\-_]+)+[\w\-.,@?^=%&:/~\\+#]*$/

# Make groups non-capturing

Regex:  /^(?:http|https):\/\/[\w\-_]+(?:\.[\w\-_]+)+[\w\-.,@?^=%&:/~\\+#]*$/

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# Decimal numbers

Regex:  /^\d+\.\d+$/m

Regex:  /^\d?\.\d+$/m

Regex:  /^\d*\.?\d*$/m

# U.S. Dollar

Regex:  /^\$(\d*\.\d{2}|\d+)$/m

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# 12 hour time

Regex:  /^(0?[1-9]|1[0-2]):[0-5][0-9]$/m

# Optional am/pm

Regex:  /^(0?[1-9]|1[0-2]):[0-5][0-9](am|pm|AM|PM)?$/m

Regex:  /^(0?[1-9]|1[0-2]):[0-5][0-9]([aApP][mM])?$/m

Timezone

Regex:  /^([0-1]?[0-9]|[2][0-3]):[0-5][0-9](:[0-5][0-9])?( [A-Z]{3})?$/m

Regex:  /^([0-1]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?( ([A-Z]{3}|GMT [-+]([0-9]|1[0-2])))?$/m

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.	Any character except newline.
\.	A period (and so on for \*, \(, \\, etc.)
^	The start of the string.
$	The end of the string.
\d,\w,\s	A digit, word character [A-Za-z0-9_], or whitespace.
\D,\W,\S	Anything except a digit, word character, or whitespace.
[abc]	Character a, b, or c.
[a-z]	a through z.
[^abc]	Any character except a, b, or c.
aa|bb	Either aa or bb.
?	Zero or one of the preceding element.
*	Zero or more of the preceding element.
+	One or more of the preceding element.
{n}	Exactly n of the preceding element.
{n,}	n or more of the preceding element.
{m,n}	Between m and n of the preceding element.
??,*?,+?, {n}?, etc.	Same as above, but as few as possible.
(expr)	Capture expr for use with \1, etc.
(?:expr)	Non-capturing group.
(?=expr)	Followed by expr.
(?!expr)	Not followed by expr.

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Regular expression cheat sheet

Special characters

\	escape special characters
.	matches any character
^	matches beginning of string
$	matches end of string
[5b-d]	matches any chars '5', 'b', 'c' or 'd'
[^a-c6]	matches any char except 'a', 'b', 'c' or '6'
R|S	matches either regex R or regex S
()	creates a capture group and indicates precedence

Quantifiers

*	0 or more (append ? for non-greedy)
+	1 or more (append ? for non-greedy)
?	0 or 1 (append ? for non-greedy)
{m}	exactly mm occurrences
{m, n}	from m to n. m defaults to 0, n to infinity
{m, n}?	from m to n, as few as possible

Special sequences

\A	start of string
\b	matches empty string at word boundary (between \wand \W)
\B	matches empty string not at word boundary
\d	digit
\D	non-digit
\s	whitespace: [ \t\n\r\f\v]
\S	non-whitespace
\w	alphanumeric: [0-9a-zA-Z_]
\W	non-alphanumeric
\Z	end of string
\g<id>	matches a previously defined group

Special sequences

(?iLmsux)	matches empty string, sets re.X flags
(?:...)	non-capturing version of regular parentheses
(?P...)	matches whatever matched previously named group
(?P=)	digit
(?#...)	a comment; ignored
(?=...)	lookahead assertion: matches without consuming
(?!...)	negative lookahead assertion
(?<=...)	lookbehind assertion: matches if preceded
(?<!...)	negative lookbehind assertion
(?(id)yes|no)	match 'yes' if group 'id' matched, else 'no'

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Unicode

Unicode indicator: \u

caf\u00E9 = cafe (e is unicode)

Unicode wildcard : \X (only for Perl and PHP)

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