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  • Are .NET's regular expressions Turing complete?

    - by Robert
    Regular expressions are often pointed to as the classical example of a language that is not Turning complete. For example "regular expressions" is given in as the answer to this SO question looking for languages that are not Turing complete. In my, perhaps somewhat basic, understanding of the notion of Turning completeness, this means that regular expressions cannot be used check for patterns that are "balanced". Balanced meaning have an equal number of opening characters as closing characters. This is because to do this would require you to have some kind of state, to allow you to match the opening and closing characters. However the .NET implementation of regular expressions introduces the notion of a balanced group. This construct is designed to let you backtrack and see if a previous group was matched. This means that a .NET regular expressions: ^(?<p>a)*(?<-p>b)*(?(p)(?!))$ Could match a pattern that: ab aabb aaabbb aaaabbbb ... etc. ... Does this means .NET's regular expressions are Turing complete? Or are there other things that are missing that would be required for the language to be Turing complete?

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  • Problem with regular expression for some special parttern.

    - by SpawnCxy
    Hi all, I got a problem when I tried to find some characters with following code: preg_match_all('/[\w\uFF10-\uFF19\uFF21-\uFF3A\uFF41-\uFF5A]/',$str,$match); //line 5 print_r($match); And I got error as below: Warning: preg_match_all() [function.preg-match-all]: Compilation failed: PCRE does not support \L, \l, \N, \U, or \u at offset 4 in E:\mycake\app\webroot\re.php on line 5 I'm not so familiar with reg expression and have no idea about this error.How can I fix this?Thanks.

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  • Confusion in RegExp Reluctant quantifier? Java

    - by Dusk
    Hi, Could anyone please tell me the reason of getting an output as: ab for the following RegExp code using Relcutant quantifier? Pattern p = Pattern.compile("abc*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group()); // ab and getting empty indices for the following code? Pattern p = Pattern.compile(".*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group());

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  • How to get N random string from a {a1|a2|a3} format string?

    - by Pentium10
    Take this string as input: string s="planets {Sun|Mercury|Venus|Earth|Mars|Jupiter|Saturn|Uranus|Neptune}" How would I choose randomly N from the set, then join them with comma. The set is defined between {} and options are separated with | pipe. The order is maintained. Some output could be: string output1="planets Sun, Venus"; string output2="planets Neptune"; string output3="planets Earth, Saturn, Uranus, Neptune"; string output4="planets Uranus, Saturn";// bad example, order is not correct Java 1.5

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  • preg_replace only replaces first occurrence then skips to next line

    - by Dom
    Got a problem where preg_replace only replaces the first match it finds then jumps to the next line and skips the remaining parts on the same line that I also want to be replaced. What I do is that I read a CSS file that sometimes have multiple "url(media/pic.gif)" on a row and replace "media/pic.gif" (the file is then saved as a copy with the replaced parts). The content of the CSS file is put into the variable $resource_content: $resource_content = preg_replace('#(url\((\'|")?)(.*)((\'|")?\))#i', '${1}'.url::base(FALSE).'${3}'.'${4}', $resource_content); Does anyone know a solution for why it only replaces the first match per line?

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  • RegExp to validate a formula (string/boolean/numeric expression)?

    - by JSteve
    I have used regExp quit a bit of times but still far from being an expert. This time I want to validate a formula (or math expression) by regExp. The difficult part here is to validate proper starting and ending parentheses with in the formula. I believe, there would be some sample on the web but I could not find it. Can somebody post a link for such example? or help me by some other means?

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  • How to find if dataTable contains column which name starts with abc

    - by VilemRousi
    In my program I have a dataTable and I´d like to know if is there a column which name starts with abc. For example I have a DataTable and its name is abcdef. I like to find this column using something like this: DataTable.Columns.Constains(ColumnName.StartWith(abc)) Because I know only part of the column name, I cannot use a Contains method. Is there any simple way how to do that? Thanks a lot.

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  • Alter Regular Expression to Return 2 Values Instead of 3 from userAgent String

    - by Jay
    I've taken a regular expression from jQuery to detect if a browser's engine is WebKit and gets it's version number, it returns 3 values extracted from the userAgent string: webkit/….…, webkit and ….… [“….…” being the version number]. I would like the regular expression to return just 2 values: webkit and ….…. I'm rubbish at regular expressions, so please can you give an explanation of the expression with your answer. The regular expression I'm currently working with and wish to improve is: /(webkit)[\/]([\w.]+)/. I appreciate all your help, thanks in advance!

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  • How to process this string via regular expression

    - by iiduce
    my string style like this: expression1/field1+expression2*expression3+expression4/field2*expression5*expression6/field3 a real style mybe like this: computer/(100)+web*mail+explorer/(200)*bbs*solution/(300) "+" and "*" represent operator "computer","web"...represent expression (100),(200) represent field num . field num may not exist. I want process the string to this: /(100)+web*+explorer/(200)bbs/(300) rules like this: if expression length is more than 3 and its field is not (200), then add brackets to it.

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  • Simple PHP form Validation and the validation symbols

    - by Cool Hand Luke UK
    Hi have some forms that I want to use some basic php validation (regular expressions) on, how do you go about doing it? I have just general text input, usernames, passwords and date to validate. I would also like to know how to check for empty input boxes. I have looked on the interenet for this stuff but I haven't found any good tutorials. Thanks

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  • Weird error using preg_match and unicode

    - by Thorpe Obazee
    if (preg_match('(\p{Nd}{4}/\p{Nd}{2}/\p{Nd}{2}/\p{L}+)', '2010/02/14/this-is-something')) { // do stuff } The above code works. However this one doesn't. if (preg_match('/\p{Nd}{4}/\p{Nd}{2}/\p{Nd}{2}/\p{L}+/u', '2010/02/14/this-is-something')) { // do stuff } Maybe someone could shed some light as to why the one below doesn't work. This is the error that is being produced: A PHP Error was encountered Severity: Warning Message: preg_match() [function.preg-match]: Unknown modifier '\'

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  • PHP & Regular expression: keyword just occurs once

    - by lauthiamkok
    Hi, how can I make sure a certain keyword just occurs once in the input with regular expression? I think there is some mistakes in the expression below as I can repeat the same keywords, if (!preg_match('/\b(.php?){1}\b/', $cfg_path)) { $error = true; echo '<error elementid="cfg_path" message="PATH - make sure you have a \'.php?\' in the path."/>'; } I just want this to be true, form.php?category=something or form.php? but not this, form.php?.php?category=something or form.php?.php? please let me know how to fix it. thanks.

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  • How to find which delimiter was used during string split (VB.NET)

    - by typoknig
    Hi all, lets say I have a string that I want to split based on several characters, like ".", "!", and "?". How do I figure out which one of those characters split my string so I can add that same character back on to the end of the split segments in question? Dim linePunctuation as Integer = 0 Dim myString As String = "some text. with punctuation! in it?" For i = 1 To Len(myString) If Mid$(entireFile, i, 1) = "." Then linePunctuation += 1 Next For i = 1 To Len(myString) If Mid$(entireFile, i, 1) = "!" Then linePunctuation += 1 Next For i = 1 To Len(myString) If Mid$(entireFile, i, 1) = "?" Then linePunctuation += 1 Next Dim delimiters(3) As Char delimiters(0) = "." delimiters(1) = "!" delimiters(2) = "?" currentLineSplit = myString.Split(delimiters) Dim sentenceArray(linePunctuation) As String Dim count As Integer = 0 While linePunctuation > 0 sentenceArray(count) = currentLineSplit(count)'Here I want to add what ever delimiter was used to make the split back onto the string before it is stored in the array.' count += 1 linePunctuation -= 1 End While

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  • How can I match a match a null byte (0x00) in the Visual Studio binary editor with a find using a re

    - by Paul K
    Open a file in the Visual Studio binary editor that contains a null byte (0x00), then use the Quick Find feature (Ctrl +F) to find null bytes. I would have thought I could use a regular expression such as \x00 to match null bytes but it doesn't work. Searching for any other hex value using this method works fine. Is this a VS bug, 'feature', or am I just missing something? Is there a work around?

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  • Regular Expression Help

    - by WizardsSleeve
    Hi There, Does anyone have a regurlar expression available which only accepts dates in the format dd/mm/yy but also has strict checking to make sure that the date is valid, including leap year support? I am coding in vb.net and am struggling to work this one out. Many Thanks

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  • Using regular expressions

    - by Tom
    What is wrong with this regexp? I need it to make $name to be letter-number only. Now it doens't seem to work at all. if (!preg_match("/^[A-Za-z0-9]$/",$name)) { $e[]="name must contain only letters or numbers"; }

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  • PHP: URL detection (regexp) includes line breaks

    - by marco92w
    I want to have a function which gets a text as the input and gives back the text with URLs made to HTML links as the output. My draft is as follows: function autoLink($text) { return preg_replace('/https?:\/\/[\S]+/i', '<a href="\0">\0</a>', $text); } But this doesn't work properly. For the input text which contains ... http://www.google.de/ ... I get the following output: <a href="http://www.google.de/<br">http://www.google.de/<br</a> /> Why does it include the line breaks? How could I limit it to the real URL? Thanks in advance!

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  • regular expression and escaping

    - by pstanton
    Sorry if this has been asked, my search brought up many off topic posts. I'm trying to convert wildcards from a user defined search string (wildcard is "*") to postgresql like wildcard "%". I'd like to handle escaping so that "%" => "\%" and "\*" => "*" I know i could replace \* with something else prior to replacing * and then swap it back, but i'd prefer not to and instead only convert * using a pattern that selects it when not proceeded by \. String convertWildcard(String like) { like = like.replaceAll("%", "\\%"); like = like.replaceAll("\\*", "%"); return like; } Assert.assertEquals("%", convertWildcard("*")); Assert.assertEquals("\%", convertWildcard("%")); Assert.assertEquals("*", convertWildcard("\*")); // FAIL Assert.assertEquals("a%b", convertWildcard("a*b")); Assert.assertEquals("a\%b", convertWildcard("a%b")); Assert.assertEquals("a*b", convertWildcard("a\*b")); // FAIL ideas welcome.

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  • awk or sed: Best way to grab [this text]

    - by Parand
    I'm trying to parse various info from log files, some of which is placed within square brackets. For example: Tue, 06 Nov 2007 10:04:11 INFO processor:receive: [someuserid], [somemessage] msgtype=[T] What's an elegant way to grab 'someuserid' from these lines, using sed, awk, or other unix utility?

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  • Change Number Format

    - by gsembilan
    I have a lot lines contains XXXXXXXXX number format. I want change number XXXXXXXXX to XX.XXX.XXX.X XXXXXXXXX = 9 digit random number Anyone can help me? Thanks in advance

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