Regular Expression Information

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Regular Expression Information

Constructs

Construct	Description
Character Escapes
\t	tab character
\r	carriage-return character
\n	line-feed (or newline) character
\x20	ASCII character expressed in hex notation (\x20 is a space)
\	the escape character (\? matches question mark, \. matches dot, and \\ matches backslash)
Character Classes
.	Any character (except the newline character if you use the Multiline option)
[aeiou]	Any character between square brackets, [aeiou] matches a lowercase vowel; [0-9] matches a digit
[^0-9]	Any character except those between square brackets, [^0-9] matches any nondigit
[A-Z&&[^P]] (* not .net)	Any character from A to Z except P
\w	A word character�same as [A-Za-z_0-9]
\d	A digit�same as [0-9]
\s	A white-space character (a space, tab, form-feed, newline, or carriage return]
\W, \D, \S	The uppercase version negates the lowercase symbol; \W means any nonword character, \D matches any nondigit, and \S is a non-white-space
\Q to \E (* not .net)	Can place literals in between
Atomic zero-width assertions (match must appear in the source string, yet don't match any character)
^	The beginning of the string, or the beginning of the line if in multiline mode
$	The end of the string, or the end of the line if in multiline mode
\b	The word boundary�the position between a \w and a \W character
\B	Not a word boundary
Quantifiers
*	Zero or more matches�same as {0,}
+	One or more matches�same as {1,}
?	Zero or one matches�same as {0,1} (or appended to other iteration operators means don't be greedy, but match as few characters as possible)
{N}	Exactly N matches
{N,}	N or more matches
{N,M}	Between N and M matches
Grouping and alternating constructs
(expr)	Captures the matched expression and assigns it a number depending on its position (/0 always refers to the entire expression match)
(expr)+	Captures one or more iterations of the matched expression, like (\.\w)+ for domain names
(?<name>expr)	Captures the matched expression and assigns it a name
(expr1\|expr2)	Matches any of the expressions enclosed in parentheses
(?=expr)	Zero-width positive look-ahead assertion�continues the matching only if the expression matches at this position, but doesn't include the expression in the match. For example, \w+(?=,) matches a word followed by a comma, without also matching the comma, or (?=Patrick)Pat matches Pat, but only if part of wors Patrick (use ?<= for lookbehind)
(?!expr)	Zero-width negative look-ahead assertion�continues the matching only if the expression doesn't match at this position. For example, \w+(?!\s) matches a word that isn't followed by a white space (use ?<! for negative lookbehind)
Back-reference and substitution constructs
\N	Back-reference to group number N
\k<name>	Back-reference to a previous named group
$N	Substitutes the last substring matched with group number N
${name}	Substitutes the last substring matched with a group with a given name
Special Options
?i	Ignore case
?m	Multiline mode
?d	UNIX line terminators

Partial Source: Visual Studio Magazine Jan. 2003

Sample Patterns

U.S. Zipcode: ^\d{5}(-?\d{4})?$
Canadian Postal Code: ^[a-zA-Z]{1}\d{1}[a-zA-Z]{1}\d{1}[a-zA-Z]{1}\d{1}$
Email: (\w+)@(\w+)\.(\w+) or .+@.+[.]+.+
URL: ^(http|https|ftp)\://[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(:[a-zA-Z0-9]*)?/?([a-zA-Z0-9\-\._\?\,\'/\\\+&%\$#\=~])*$
Domain: ^[a-z,0-9,-]{1,63}\\.(com|org|net|gov|mil)$
Telephone: ^$?\d{3}$?[-\s]?\d{3}[-\s]?\d{4}$
Credit Card Number (16-digit): ^[\d]{4}(?<grpDel>[-\s]?)[\d]{4}\k<grpDel>[\d]{4}\k<grpDel>[\d]{4}$ (* remembers delimiter character used and must be same one if used again)
3 Digit number: ^\d\d\d$
find duplicate words in text (if occurs 3 times would show up twice): (?<word>\b\w+\b)(?=.+\b\k<word>\b)
All MM-./DD-./YYYY dates: (0[1-9]|1[012])[-\./](0[1-9]|[12][0-9]|3[01])[-\./](19|20)\d\d
All 3, 4, or 5 character words: \b\w{3,5}\b
VB variable declarations: \b{Dim|Public|private)\s+(\w+)\s+As\s+(New\s+)?(\w+)
single or double-quoted strings: ("|')[^\1]+\1
ensure a1 or b2: ((?a)|b)(?(foundA)1|2)

VB.Net Code

Imports System.Text.RegularExpressions
Dim re as New RegEx([AEIOU]\w\w\w") Dim strText As String = "Anne Bob Eric"
Dim m as Match
For each m in re.Matches(strText)
Console.WriteLine("{0} at index {1}", m.Value, m.Index)
Next
'is entered text 3 digit number
Dim re As New Regex("^\d\d\d$")
If re.IsMatch(tbValue.Text) Then
'...
End If
'find all 4-char words at the beginning of each line
Dim re As New Regex("^\w\w\w\w\b", RegexOptions.Multiline)
find unique words in text - matches any word in the text that isn't followed by another instance of the same word - will match the sole occurrence of unique words or the last occurrence of a repeated word
Dim p as String = "(?\b\w+\b)(?!.+\b\k\b)"
Dim re As New Regex(p)
For Each m As Match in re.Matches(text)
Console.Write (m.Value & " ")
Next
'count words in sentence
Dim strText As String = "Here is a sample sentence"
Dim re As New Regex("\w+")
Console.WriteLine(re.Matches(strText).Count)
'find all dates in document text
Dim re As New Regex("\b1?\d/[123]?\d/\d{4}\b")
Dim m As Match
For Each m In re.Matches(strDocument)
Console.WriteLine(m.Value)
Next
'get all VB declarations in document
Dim strPattern As String = "\b(Dim|Private|Public)\s+(\w+)\s+As\s+(New\s+)?(\w+)"
Dim re As New Regex(pattern, RegexOptions.Multiline Or RegexOptions.IgnoreCase)
Dim m As Match
For Each m In re.Matches(strSource)
Console.WriteLine("variable {0} of type {1}", m.Groups(2).Value, m.Groups(4).Value)
Next
'read/parse csv file
Imports System.IO
Imports System.Text.RegularExpressions

Dim sr As New StreamReader("c:\info.csv")
Dim text As String = sr.ReadToEnd
sr.Close()

Dim pattern As String = _
"^\s*""(?<first>[^""]+)""\s*," & _
"\s*""(?<last>[^""]+)""\s*," & _
"\s*(?<salary>\d+(\.\d\d)?)\s*$"
Dim re As New Regex(pattern, RegexOptions.Multiline)

Dim m As Match = re.Match(text)
Do While m.Success
Console.WriteLine("FirstName: {0}, " _
& "LastName: {1}, Salary: {2}", _
m.Groups("first").Value, _
m.Groups("last").Value, _
m.Groups("salary").Value)
m = m.NextMatch()
Loop
'generic global search/replace
Dim re As New Regex("Windows (95|98|NT|2000)") Console.WriteLine(re.Replace(strText, "Windows XP"))
'change names from "title firstname lastname" to "title lastname, firstname" format
Dim re As New Regex( "(?<title>Mr\.|Mrs\.)\s+" & _ "(?<first>\w+)\s+(?<last>\w+)")
Console.WriteLine(re.Replace(txt, "${title} ${last}, ${first}"))
Replace all and tags
Dim re As Text.RegularExpressions.Regex = New Text.RegularExpressions.Regex("<span.*?>", Text.RegularExpressions.RegexOptions.IgnoreCase)
lbl.Text = re.Replace(lbl.Text, "")
re = New Text.RegularExpressions.Regex("<\/span>", Text.RegularExpressions.RegexOptions.IgnoreCase)
lbl.Text = re.Replace(lbl.Text, "")
re = Nothing
'more advanced replacement call
Sub Main()
Dim strText As String = "x=12+23, y=34-18"
'replace all sums and subtractions with their result
Dim re As New Regex("(\d+)([-+])(\d+)")
Dim strRes As String = re.Replace(strText, AddressOf EvalOp)
Console.WriteLine(strRes)
End Sub

Function EvalOp(ByVal m As Match) As String
Dim op1 As Long = CLng(m.Groups(1).Value)
Dim op2 As Long = CLng(m.Groups(3).Value)
Select Case m.Groups(2).Value
Case "+"
Return CStr(op1 + op2)
Case "-"
Return CStr(op1 - op2)
End Select
End Function

VBScript Code

'test string
Set regEx = New RegExp
regEx.IgnoreCase = True
regEx.Pattern = "^\d\d\d$"
If regEx.Test(strFileName) Then '.Net Test=IsMatch
...
End If

'count words in string
Dim regEx As New RegExp
regEx.Pattern = "\w+"
Set regExMatches = regEx.Execute(strInput)
Response.Write regExMatches.Count & " "

'do replacements/conversions
regEx.Global = True
strText = regEx.Replace(sInput, sReplacement)
strText = regEx.Replace(strInput, AddressOf function1)
'Mr. Kevin Mahoney to Mr. Mahoney, Kevin
Set re = New RegEx("(Mr\.|Mrs\.)\s+(\w+)\s+(\w+)")
Console WriteLine( re.Replace(strInput, "$1 $3, $2") )

'count matches and loop through
Set regExMatches = regEx.Execute(strInput)
Response.Write regExMatches.Count & " "
For Each regExMatch in regExMatches
 Response.Write regExMatch.Value & " "
 Response.Write regExMatch.subMatches(0) & " " '.Net suMatches(0)=Groups(0)
Next

'read in CSV file
'sample line: "John", "Doe", 51345.00
strPattern = "^\s*""(?<fname>[^""]+)""\s*," _
 & "\s*""(?<lname>[^""]+)""\s*," _
 & "\s*(?<salary>\d+(\.\d\d)?)\s*$"
'use multiline option since input has line breaks - can also use RedExOptions.Compiled if expect to use same object often during application's lifetime - the first call takes longer and it stays in memory
Set re = New RegEx(strPattern, RexExOptions.Multiline)
'don't get all matches at once if want to quit after find one or will take too long to read all into memory
Set reMatch = re.Match(strInput)
Do While reMatch.Success
 Console.WriteLine("First Name: " & reMatch.Groups("fname").value _
 & ", Last Name: " & reMatch.Groups("lname").value _
 & ", Salary: " & reMatch.Groups("salary").value
 reMatch = re.NextMatch()
Loop