Regular Expressions

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regular expression (def)

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provides a concise and flexible means to "match" (specify and recognize) strings of text, such as particular characters, words, or patterns of characters. Common abbreviations for "regular expression" include regex and regexp

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look for all Jennifer/Jen/Jenny followed by last name

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(Jeniffer!Jen!Jenny)\b\w+\b

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Python use of regex

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import re
f = open('file.txt')
strToSearch = ""
for line in f:
strToSearch != line
print(strToSearch) --- in A018sdakldsakd
pathFinder1 = re.compile('A018')

findPat1 = re.search(patFinder1, strToSearch)

printf(findPat1.group()) --out A018
printf(findPat1.start()) --out 0
printf(findPat1.end()) --out 4
printf(findPat1.span()) --out (0,4)

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? indicate

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The question mark indicates there is zero or one of the preceding element. For example, colou?r matches both "color" and "colour".

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* indicates

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The asterisk indicates there is zero or more of the preceding element. For example, ab*c matches "ac", "abc", "abbc", "abbbc", and so on.

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+ indicates

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The plus sign indicates there is one or more of the preceding element. For example, ab+c matches "abc", "abbc", "abbbc", and so on, but not "ac"

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JS function to process regex

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function editNodeText( regex, input, helpId, helpMessage)

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(a|b)*

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denotes the set of all strings with no symbols other than a and b, including the empty string: {ε, a, b, aa, ab, ba, bb, aaa, ...}

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ab*(c|ε)

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denotes the set of strings starting with a, then zero or more bs and finally optionally a c: {a, ac, ab, abc, abb, abbc, ...}

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∅

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(empty set) ∅ denoting the set ∅.

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ε

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(empty string) ε denoting the set containing only the "empty" string, which has no characters at all.

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a

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(literal character) a in Σ denoting the set containing only the character a.

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escape character

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A number of special characters or meta characters are used to denote actions or delimit groups; but it is possible to force these special characters to be interpreted as normal characters by preceding them with a defined escape character, usually the backslash "\". For example, a dot is normally used as a "wild card" metacharacter to denote any character, but if preceded by a backslash it represents the dot character itself

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pattern c.t matches

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"cat", "cot", "cut", and non-words such as "czt" and "c.t"; but c\.t matches only "c.t"

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.

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Matches any single character (many applications exclude newlines)

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a.c matches ?

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"abc"

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[a.c] matches ?

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"a", ".", or "c"

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[ ] matches ?

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A bracket expression. Matches a single character that is contained within the brackets. For example, [abc] matches "a", "b", or "c". [a-z] specifies a range which matches any lowercase letter from "a" to "z".

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[abcx-z] matches ?

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"a", "b", "c", "x", "y", or "z"

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[a-cx-z] matches ?

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"a", "b", "c", "x", "y", or "z"

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[^ ]

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Matches a single character that is not contained within the brackets

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[^abc] matches

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[^abc] matches any character other than "a", "b", or "c"

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^ matches

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Matches the starting position within the string. In line-based tools, it matches the starting position of any line.

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$ matches

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Matches the ending position of the string or the position just before a string-ending newline. In line-based tools, it matches the ending position of any line.

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* matches

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Matches the preceding element zero or more times. For example, ab*c matches "ac", "abc", "abbbc", etc

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[xyz]*

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"", "x", "y", "z", "zx", "zyx", "xyzzy"

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.at matches

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matches any three-character string ending with "at", including "hat", "cat", and "bat".

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[hc]at matches

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[hc]at matches "hat" and "cat".

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[^b]at matches

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[^b]at matches all strings matched by .at except "bat".

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^[hc]at matches

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"hat" and "cat", but only at the beginning of the string or line.

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[hc]at$ matches

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"hat" and "cat", but only at the end of the string or line.

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\[.\]

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matches any single character surrounded by "[" and "]" since the brackets are escaped, for example: "[a]" and "[b]".

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Set
"Handel"
"Hondel"
"Haendel"
what pattern matches this

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H(o|ae?)ndel

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boolean or

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grey|gray

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Grooping

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gray|grey <=> gr(a|e)y

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\s

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expr for space

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\w

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expr for character

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\.

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any character possib;e

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\d

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any number

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\D

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anything but a number

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\s

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space

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\S

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anything but a space

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0 or 1 repetitions of whatever code precedes it

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\?

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zero or more repetitions of whatever code precedes it

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\*

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n repetitions repetition of whatever code precedes it

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{n}

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[a-z]

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1 of any lower case

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all sentences that start with Cat

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[^Cat\s\w+$]

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php use of regex

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$matchName = $reg.grep("%patterntoserach%", $randomArray);

for each ($matchName as $result)
{ echo $reset, "<br /> <br />";
}

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^ matches

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begining of a text

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email pattern match

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[A-Za-z0-9._\%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}

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match pattern string - must have at lease 1 upper case letter

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\A(?=[-_a-zA-Z0-9]*?[A-Z])
This string must have at lease 1 upper case letter

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match pattern string - must have at lease 1 upper case letter and 1 upper case number

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\A(?=[-_a-zA-Z0-9]*?[A-Z])
(?=[-_a-zA-Z0-9]*?[0-9])

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\z

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end of a string

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\A

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begining of the string

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phone patter

412-537-5555
(412)-537-5555

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%\(?[0-9]{3}\)?-?[0-9]{3}[-. ]?[0-9]{4}%

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date pattern

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%(0?[1-9]|[12][0-9]|3[01])[- /.](0?[1-9]|[12][0-9]|3[01])[- /.](19|20)?[0-9]{2}%

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(?=)

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Match what proceeds equals if what follows equals matches

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^(Derbylane)

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the sentence starts with Derby lane

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\s+

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unknown number of psaces