Regular Expressions

What is a Regular Expression

A regular expression is a pattern of text that consists of ordinary characters (for example, letters a through z) and special characters, known as metacharacters. The pattern describes one or more strings to match when searching a body of text. The regular expression serves as a template for matching a character pattern to the string being searched.

A regular expression is a string that describes or matches a set of strings. It is often called a pattern as it describes set of strings.

Given underneath is one of the most widely used and ever confused BackLash character. The remaining expressions are serialized below that

A backslash (\) instructs QuickTest to treat the next character as a literal character, if it is otherwise a special character. The backslash (\) can also instruct QuickTest to recognize certain ordinary characters as special characters. For example, QuickTest recognizes \n as the special newline character.
For example:
w matches the character w
\w is a special character that matches any word character including underscore
For example, in QTP, while entering the URL of a website,
http://mercurytours.mercuryinteractive.com
The period would be mistaken as an indication of a regular expression. To indicate that the period is not part of a regular expression, you would enter it as follows:
mercurytours\.mercuryinteractive\.com Note: If a backslash character is used before a character that has no special meaning, the backslash is ignored. For example, \z matches z.


Few Snippets involving Regular Expressions


Regular Express1.vbs . This function regular expression will match a string/value/pattern out of Strings
Function RegExpTest(patrn, strng)
Dim regEx, Match, Matches ' Create variable.
Set regEx = New RegExp ' Create a regular expression.
regEx.Pattern = patrn ' Set pattern.
regEx.IgnoreCase = True ' Set case insensitivity.
regEx.Global = True ' Set global applicability.
Set Matches = regEx.Execute(strng) ' Execute search.
For Each Match in Matches ' Iterate Matches collection.
RetStr = RetStr & "Match found at position "& Match.FirstIndex & " Match Value is " & Match.Value & VBCRLF
Next
RegExpTest = RetStr
End Function
MsgBox(RegExpTest("is.", "IS1 is2 IS3 is4"))

You can also return the value that the calling function back to a variable and then print it as follows
Function RegExpTest(patrn, strng)
Dim regEx, Match, Matches ' Create variable.
Set regEx = New RegExp ' Create a regular expression.
regEx.Pattern = patrn ' Set pattern.
regEx.IgnoreCase = True ' Set case insensitivity.
regEx.Global = True ' Set global applicability.
Set Matches = regEx.Execute(strng) ' Execute search.
For Each Match in Matches ' Iterate Matches collection.
RetStr = RetStr & "Match found at position "& Match.FirstIndex & " Match Value is " & Match.Value & VBCRLF
Next
RegExpTest = RetStr
End Function
RetStr = RegExpTest("is.", "IS1 is2 IS3 is4")
Msgbox RetStr

Regular Expressions to Search from strings(Keywords) from Internet Explorer page stored on desktop

Dim ObjRegExp, IEinstance
Set IEinstance =CreateObject("InternetExplorer.Application")
cnt=1
IEinstance.Navigate "C:\Documents and Settings\gseth\Desktop\Gmail.htm"
IEinstance.visible=true
lvVal = IEinstance.Document.body.innertext
msgbox “ The Contents of Gmail are “ &lvVal
Dim Searchkeys(5000)
Searchkeys(0) ="Create an Account"
Searchkeys(1)="Gmail"
Searchkeys(2)="Google"

For keyval = 0 to ubound(SearchKeys)
Found = False
If SearchKeys(keyval) <> "" Then
'Msgbox "Searching for " & SearchKeys(keyval)
Set ObjRegExp = new regexp
ObjRegExp.pattern = SearchKeys(keyval)
ObjRegExp.Global = True
ObjRegExp.Ignorecase = True
Set matches = ObjRegExp.Execute(lvVal)
For each objmatch in matches
tmpVar = objmatch.value
If SearchKeys(keyval) = CStr(tmpVar) Then
Msgbox "Count is " &cnt & " Matching value is " &tmpVar
cnt = cnt+1
End If
Next

Else
Exit For
End If
Next
IEinstance.Quit
Set IEinstance = Nothing

Regular Expression for Searching a keyword from the Text File (Notepad File) and displaying it

Dim ObjRegExp,objFSO, objReadFile, contents,var
Const conForReading=1

Set objFSO=CreateObject("Scripting.FileSystemObject")
Set objReadFile=objFSO.OpenTextFile("C:\Documents and Settings\kdhote.SHALL20-1\Desktop\VB Scripting Code Snippets.txt", 1 , False)
contents=objReadFile.ReadAll
msgbox " the contents are" &contents
var="October"
Set ObjRegExp = new regexp
ObjRegExp.pattern = var
ObjRegExp.Global = True
ObjRegExp.Ignorecase = True
Set matches = ObjRegExp.Execute(contents)
For each objmatch in matches
tmpVar = objmatch.value
If var = CStr(tmpVar) Then
Msgbox "Count is " &cnt & " Matching value is " &tmpVar
cnt = cnt+1
End If
Next

Set objFSO=Nothing
Set objReadFile=Nothing



Expressions & Explanation
Special characters and sequences are used in writing patterns for regular expressions. The following describes the characters and sequences that can be used.


\
Marks the next character as either a special character or a literal. For example, "n" matches the character "n". "\n" matches a newline character. The sequence "\\" matches "\" and "\(" matches "(".

^
Matches the beginning of input.

$
Matches the end of input.

*
Matches the preceding character zero or more times. For example, "zo*" matches either "z" or "zoo".

+
Matches the preceding character one or more times. For example, "zo+" matches "zoo" but not "z".

?
Matches the preceding character zero or one time. For example, "a?ve?" matches the "ve" in "never".

.
Matches any single character except a newline character.

(pattern)
Matches pattern and remembers the match. The matched substring can be retrieved from the resulting Matches collection, using Item [0]...[n]. To match parentheses characters ( ), use "\(" or "\)".

xy
Matches either x or y. For example, "zwood" matches "z" or "wood". "(zw)oo" matches "zoo" or "wood".

{n}
n is a nonnegative integer. Matches exactly n times. For example, "o{2}" does not match the "o" in "Bob," but matches the first two o's in "foooood".

{n,}
n is a nonnegative integer. Matches at least n times. For example, "o{2,}" does not match the "o" in "Bob" and matches all the o's in "foooood." "o{1,}" is equivalent to "o+". "o{0,}" is equivalent to "o*".

{n,m}
m and n are nonnegative integers. Matches at least n and at most m times. For example, "o{1,3}" matches the first three o's in "fooooood." "o{0,1}" is equivalent to "o?".

[xyz]
A character set. Matches any one of the enclosed characters. For example, "[abc]" matches the "a" in "plain".

[^xyz]
A negative character set. Matches any character not enclosed. For example, "[^abc]" matches the "p" in "plain".

[a-z]
A range of characters. Matches any character in the specified range. For example, "[a-z]" matches any lowercase alphabetic character in the range "a" through "z".

[^m-z]
A negative range characters. Matches any character not in the specified range. For example, "[m-z]" matches any character not in the range "m" through "z".

\b
Matches a word boundary, that is, the position between a word and a space. For example, "er\b" matches the "er" in "never" but not the "er" in "verb".

\B
Matches a non-word boundary. "ea*r\B" matches the "ear" in "never early".

\d
Matches a digit character. Equivalent to [0-9].

\D
Matches a non-digit character. Equivalent to [^0-9].

\f
Matches a form-feed character.

\n
Matches a newline character.

\r
Matches a carriage return character.

\s
Matches any white space including space, tab, form-feed, etc. Equivalent to "[ \f\n\r\t\v]".

\S
Matches any nonwhite space character. Equivalent to "[^ \f\n\r\t\v]".

\t
Matches a tab character.

\v
Matches a vertical tab character.

\w
Matches any word character including underscore. Equivalent to "[A-Za-z0-9_]".

\W
Matches any non-word character. Equivalent to "[^A-Za-z0-9_]".

\num
Matches num, where num is a positive integer. A reference back to remembered matches. For example, "(.)\1" matches two consecutive identical characters.

\n
Matches n, where n is an octal escape value. Octal escape values must be 1, 2, or 3 digits long. For example, "\11" and "\011" both match a tab character. "\0011" is the equivalent of "\001" & "1". Octal escape values must not exceed 256. If they do, only the first two digits comprise the expression. Allows ASCII codes to be used in regular expressions.

\xn
Matches n, where n is a hexadecimal escape value. Hexadecimal escape values must be exactly two digits long. For example, "\x41" matches "A". "\x041" is equivalent to "\x04" & "1". Allows ASCII codes to be used in regular expressions.



Why are Regular Expressions important in QTP

In order to carry out tests in QTP each and every objects are searched in the object repository (OR). An object in a real time application sometime has properties that keep changing from time to ti for which at the time of execution the script fails. To overcome this, regular expressions are used for that object’s particular dynamic property.

How to create Regular Expressions in QTP

Below Link is very useful for explaining how to create regular expressions in QTP

http://www.cinterviews.com/2010/10/to-create-regular-expression-in-qtp.html

Below are couple of Youtube Links of Regular Expressions


Introduction to Regular Expressions Part 1
http://www.youtube.com/watch?v=Au6ghl57ovc

Introduction to Regular Expressions Part 2
http://www.youtube.com/watch?v=MgnIFM0H9dk&NR=1