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• What does this regex mean and why

  - by Kalec

  $ sed "s/\(^[a-z,0-9]*\)\(.*\)\( [a-z,0-9]*$\)/\1\2 \1/g" desired_file_name I apreciate it even if you only explain part of it or at lest structure it with words as in s\alphanumerical_at_start\something\alphanumerical_at_end\something_else\global Could someone explain what that means, why and are all regEx so ... awful ? I know that it replaces the first lowcase alphanumerical word with the last one. But could you explain bit by bit what's going on here ? what's with all the /\ and \(.*\)\ and everything else ? I'm just lost. EDIT: Here is what I do get: (^[a-z0-9]*) starting with a trough z and 0 trough 9; and [a-z,0-9]*$ is the same but the last word (however [0-9,a-z] = just first 2 characters / first character, or the entire word ?). Also: what does the * or the \(.*\)\ even mean ?

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• Looking for good Regex book

  - by Cyberherbalist

  I've been trying to get a good grounding with Regular Expressions, and am looking for a single book to do so. I've been going through Amazon.com's listings on this subject, and I've identified a few possibilities, but am unsure which would be best for a C# developer who can write very simple Regexs, but wants to learn more. On a scale of 0-9 where 0 is knowing how to spell "Regex" but nothing else, and 9 where I could write a book on the subject out of my own head, I would place myself at 2. Which of the following would be your choice: Mastering Regular Expressions by Jeffrey E F Friedl Regular Expressions Cookbook by Jan Goyvaerts and Steven Levithan Sams Teach Yourself Regular Expressions in 10 Minutes by Ben Forta Beginning Regular Expressions (Programmer to Programmer) by Andrew Watt Regular Expression Recipes for Windows Developers: A Problem-Solution Approach by Nathan A. Good Regular Expression Recipes: A Problem-Solution Approach by Nathan A. Good Now, according to Amazon, "Regular Expressions Cookbook" (REC) above is rated the highest according to user ratings, but only based on 20 reviews. The first one, "Mastering Regular Expressions" (MRE) is rated second based on 140 reviews. This alone suggests that MRE might be by far the best one. But is it best for a relative beginner? Would I perhaps be better getting "Beginning Regular Expressions" (BRE) instead, to start with? Please help me resolve my confusion!

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• Regex syntax question - trying to understand

  - by Asaf Chertkoff

  i don't know if this question belong here or no, but it is worth a shot. i'm a self taught php programmer and i'm only now starting to grasp the regex stuff. i'm pretty aware of its capabilities when it is done right, but this is something i need to dive in too. so maybe someone can help me, and save me so hours of experiment. i have this string: here is the <a href="http://www.google.com" class="ttt" title="here"><img src="http://www.somewhere.com/1.png" alt="some' /></a> and there is <a href="#not">not</a> a chance... now, i need to perg_match this string and search for the a href tag that has an image in it, and replace it with the same tag with a small difference: after the title attribute inside the tag, i'll want to add a rel="here" attribute. of course, it should ignore links (a href's) that doesn't have img tag inside. help will be appreciated, thanks.

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• JavaScript Regex Problem

  - by oraclee

  Hi all; Csharp Regex Pattern: Regex rg = new Regex("(?i)(?<=>)[^<]+(?=</TD>)"); JavaScript Regex Pattern: var pattern = (?i)(?<=>)[^<]+(?=</TD>); var result = str.match(pattern); Csharp Regex pattern work, but javascript regex pattern not work pls help ?

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• Trying to do a batch rename, can't figure out the proper RegEx

  - by trezy

  I'm trying to rename my movie collection. All of the files are currently named using dots instead of spaces, i.e. Men.in.Black.avi. I want to replace all of the dots with spaces which isn't terribly difficult, but I need to preserve the last dot for the file extension, i.e. .avi, .mp4, .ogg, etc. My Googling has provided no solutions. I'm also a Javascript developer and could see some snazzy applications for it. So, any suggestions?

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• simscan's regex

  - by alexus

  -bash-3.2# cat /var/qmail/control/simcontrol :clam=yes,spam=yes,spam_hits=7.0,regex=^Subject\072.*(7.|8.)\%.*:(?m)\.ru\/\n{21} -bash-3.2# cat ./cur/msg.1268526916.764928.8759:2,S | pcregrep -M '(?m)\.ru\/\n{21}' Party's over for Clinton http://260.noonwife.ru/ of because Abraham is large Confessional murdered the for -bash-3.2# grep -c REGEX /var/log/qmail/smtpd/@* /var/log/qmail/smtpd/@400000004b9c134f0095ecdc.s:25 /var/log/qmail/smtpd/@400000004b9c144c2748a9dc.s:6 /var/log/qmail/smtpd/@400000004b9c16eb2ac491fc.s:12 /var/log/qmail/smtpd/@400000004b9c1c61239185ac.s:28 /var/log/qmail/smtpd/@400000004b9c216a3013fdb4.s:29 /var/log/qmail/smtpd/@400000004b9c26b11fb5263c.s:22 /var/log/qmail/smtpd/@400000004b9c2b2505d2035c.s:25 /var/log/qmail/smtpd/@400000004b9c2ec3139530f4.s:12 /var/log/qmail/smtpd/@400000004b9c312c160d7454.s:4 -bash-3.2# first regex works, yet i can't get it to match second, even though pcregrep matches it using same regex just fine any ideas?

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• Efficiently Combine MatchCollections in .Net Regex

  - by Laramie

  In the simplified example, there are 2 Regular Expressions, one case sensitive, the other not. The idea would be to efficiently create an IEnumerable collection (see "combined" below) combining the results. string test = "abcABC"; string regex = "(?<grpa>a)|(?<grpb>b)|(?<grpc>c)]"; Regex regNoCase = new Regex(regex, RegexOptions.IgnoreCase); Regex regCase = new Regex(regex); MatchCollection matchNoCase = regNoCase.Matches(test); MatchCollection matchCase = regCase.Matches(test); //Combine matchNoCase and matchCase into an IEnumerable IEnumerable<Match> combined= null; foreach (Match match in combined) { //Use the Index and (successful) Groups properties //of the match in another operation } In practice, the MatchCollections might contain thousands of results and be run frequently using long dynamically created REGEXes, so I'd like to shy away from copying the results to arrays, etc. I am still learning LINQ and am fuzzy on how to go about combining these or what the performance hits to an already sluggish process will be.

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• php regex expression to get title

  - by 55skidoo

  I'm trying to strip content titles out of the middle of text strings. Could I use regex to strip everything out of this string except for the title (in italics) in these strings? Or is there a better way? Joe User wrote a blog post called The 10 Best Regex Expressions in the category Regex. Jane User wrote a blog post called Regex is Hard! in the category TechProblems. I've tried to come up with a regex expression to cover this, but I think it might need two. The trick is that the text in bold is always the same, so you could search for that, like this: regex: delete everything before and including wrote a blog post called regex: delete in the category and everything after it.

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• Scala regex Named Capturing Groups

  - by Brent

  In scala.util.matching.Regex trait MatchData I see that there support for groupnames (Named Capturing Groups) But since Java does not support groupnames until version 7 as I understand it, Scala version 2.8.0.RC4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6. gives me this exception: scala> val pattern = """(?<login>\w+) (?<id>\d+)""".r java.util.regex.PatternSyntaxException: Look-behind group does not have an obvio us maximum length near index 11 (?<login>\w+) (?<id>\d+) ^ at java.util.regex.Pattern.error(Pattern.java:1713) at java.util.regex.Pattern.group0(Pattern.java:2488) at java.util.regex.Pattern.sequence(Pattern.java:1806) at java.util.regex.Pattern.expr(Pattern.java:1752) at java.util.regex.Pattern.compile(Pattern.java:1460) So the question is Named Capturing Groups supported in Scala? If so any examples out there? If not I might look into the Named-Regexp lib from clement.denis.

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• Is regex too slow? Real life examples where simple non-regex alternative is better

  - by polygenelubricants

  I've seen people here made comments like "regex is too slow!", or "why would you do something so simple using regex!" (and then present a 10+ lines alternative instead), etc. I haven't really used regex in industrial setting, so I'm curious if there are applications where regex is demonstratably just too slow, AND where a simple non-regex alternative exists that performs significantly (maybe even asymptotically!) better. Obviously many highly-specialized string manipulations with sophisticated string algorithms will outperform regex easily, but I'm talking about cases where a simple solution exists and significantly outperforms regex. What counts as simple is subjective, of course, but I think a reasonable standard is that if it uses only String, StringBuilder, etc, then it's probably simple.

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• Can the csv format be defined by a regex?

  - by Spencer Rathbun

  A colleague and I have recently argued over whether a pure regex is capable of fully encapsulating the csv format, such that it is capable of parsing all files with any given escape char, quote char, and separator char. The regex need not be capable of changing these chars after creation, but it must not fail on any other edge case. I have argued that this is impossible for just a tokenizer. The only regex that might be able to do this is a very complex PCRE style that moves beyond just tokenizing. I am looking for something along the lines of: ... the csv format is a context free grammar and as such, it is impossible to parse with regex alone ... Or am I wrong? Is it possible to parse csv with just a POSIX regex? For example, if both the escape char and the quote char are ", then these two lines are valid csv: """this is a test.""","" "and he said,""What will be, will be."", to which I replied, ""Surely not!""","moving on to the next field here..."

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• Java regex patterns - compile time constants or instance members?

  - by KepaniHaole

  Currently, I have a couple of singleton objects where I'm doing matching on regular expressions, and my Patterns are defined like so: class Foobar { private final Pattern firstPattern = Pattern.compile("some regex"); private final Pattern secondPattern = Pattern.compile("some other regex"); // more Patterns, etc. private Foobar() {} public static Foobar create() { /* singleton stuff */ } } But I was told by someone the other day that this is bad style, and Patterns should always be defined at the class level, and look something like this instead: class Foobar { private static final Pattern FIRST_PATTERN = Pattern.compile("some regex"); private static final Pattern SECOND_PATTERN = Pattern.compile("some other regex"); // more Patterns, etc. private Foobar() {} public static Foobar create() { /* singleton stuff */ } } The lifetime of this particular object isn't that long, and my main reason for using the first approach is because it doesn't make sense to me to hold on to the Patterns once the object gets GC'd. Any suggestions / thoughts?

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• .NET RegEx "Memory Leak" investigation

  - by Kevin Pullin

  I recently looked into some .NET "memory leaks" (i.e. unexpected, lingering GC rooted objects) in a WinForms app. After loading and then closing a huge report, the memory usage did not drop as expected even after a couple of gen2 collections. Assuming that the reporting control was being kept alive by a stray event handler I cracked open WinDbg to see what was happening... Using WinDbg, the !dumpheap -stat command reported a large amount of memory was consumed by string instances. Further refining this down with the !dumpheap -type System.String command I found the culprit, a 90MB string used for the report, at address 03be7930. The last step was to invoke !gcroot 03be7930 to see which object(s) were keeping it alive. My expectations were incorrect - it was not an unhooked event handler hanging onto the reporting control (and report string), but instead it was held on by a System.Text.RegularExpressions.RegexInterpreter instance, which itself is a descendant of a System.Text.RegularExpressions.CachedCodeEntry. Now, the caching of Regexs is (somewhat) common knowledge as this helps to reduce the overhead of having to recompile the Regex each time it is used. But what then does this have to do with keeping my string alive? Based on analysis using Reflector, it turns out that the input string is stored in the RegexInterpreter whenever a Regex method is called. The RegexInterpreter holds onto this string reference until a new string is fed into it by a subsequent Regex method invocation. I'd expect similar behaviour by hanging onto Regex.Match instances and perhaps others. The chain is something like this: Regex.Split, Regex.Match, Regex.Replace, etc Regex.Run RegexScanner.Scan (RegexScanner is the base class, RegexInterpreter is the subclass described above). The offending Regex is only used for reporting, rarely used, and therefore unlikely to be used again to clear out the existing report string. And even if the Regex was used at a later point, it would probably be processing another large report. This is a relatively significant problem and just plain feels dirty. All that said, I found a few options on how to resolve, or at least work around, this scenario. I'll let the community respond first and if no takers come forward I will fill in any gaps in a day or two.

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• Regex one-to-one mapping pattern replace

  - by polygenelubricants

  How would you use regex to write a function that replaces all lowercase letters with uppercase and vice versa? Note: this is NOT a homework question. See also my previous explorations of regex: Regex split into overlapping strings (Alan Moore's answer is especially instructive) Can you use zero-width matching regex in String split? (my solution exploits a known Java regex bug with regards to non-obvious length lookbehind!)

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• Does REGEX differ from PHP to Python

  - by daemonfire300

  hi there, I found this post: http://stackoverflow.com/questions/118143/python-regex-vs-php-regex but I actually did not get if Python's REGEX syntax matches PHP's REGEX syntax. I started to convert some of my old PHP code to python (due to g's appengine etc.), and now I would like to know whether the regex is 100% convertable, by simple copy & paste. regards,

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• Python regex compile (with re.VERBOSE) not working

  - by bfloriang

  I'm trying to put comments in when compiling a regex but when using the re.VERBOSE flag I get no matchresult anymore. (using Python 3.3.0) Before: regex = re.compile(r"Duke wann", re.IGNORECASE) print(regex.search("He is called: Duke WAnn.").group()) Output: Duke WAnn After: regex = re.compile(r''' Duke # First name Wann #Last Name ''', re.VERBOSE | re.IGNORECASE) print(regex.search("He is called: Duke WAnn.").group())` Output: AttributeError: 'NoneType' object has no attribute 'group'

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• Regex: How do I match some regex logic 1 or more times?

  - by tom

  I already have some regex logic which says to look for a div tag with class=something. However, this might occur more than once (one after another). You can't simply add square brackets around that complex regex logic already (e.g. [:some complicated regex logic already existing:]* -- so how do you do it in regex? I want to avoid having to use the programming language logic to append that regex logic after itself if I can... Thanks

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• How do you capture a group with regex?

  - by Sylvain

  Hi, I'm trying to extract a string from another using regex. I'm using the POSIX regex functions (regcomp, regexec ...), and I fail at capturing a group ... For instance, let the pattern be something as simple as "MAIL FROM:<(.*)>" (with REG_EXTENDED cflags) I want to capture everything between '<' and '' My problem is that regmatch_t gives me the boundaries of the whole pattern (MAIL FROM:<...) instead of just what's between the parenthesis ... What am I missing ? Thanks in advance, edit: some code #define SENDER_REGEX "MAIL FROM:<(.*)>" int main(int ac, char **av) { regex_t regex; int status; regmatch_t pmatch[1]; if (regcomp(&regex, SENDER_REGEX, REG_ICASE|REG_EXTENDED) != 0) printf("regcomp error\n"); status = regexec(&regex, av[1], 1, pmatch, 0); regfree(&regex); if (!status) printf( "matched from %d (%c) to %d (%c)\n" , pmatch[0].rm_so , av[1][pmatch[0].rm_so] , pmatch[0].rm_eo , av[1][pmatch[0].rm_eo] ); return (0); } outputs: $./a.out "012345MAIL FROM:<abcd>$" matched from 6 (M) to 22 ($) solution: as RarrRarrRarr said, the indices are indeed in pmatch[1].rm_so and pmatch[1].rm_eo hence regmatch_t pmatch[1]; becomes regmatch_t pmatch[2]; and regexec(&regex, av[1], 1, pmatch, 0); becomes regexec(&regex, av[1], 2, pmatch, 0); Thanks :)

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• libstdc++ - compiling failing because of tr1/regex

  - by Radek Šimko

  I have these packages installed on my OpenSUSE 11.3: i | libstdc++45 | Standard shared library for C++ | package i | libstdc++45-devel | Contains files and libraries for development | package But when i'm trying to compile this C++ code: #include <stdio.h> #include <tr1/regex> using namespace std; int main() { int test[2]; const tr1::regex pattern(".*"); test[0] = 1; if (tr1::regex_match("anything", pattern) == false) { printf("Pattern does not match.\n"); } return 0; } using g++ -pedantic -g -O1 -o ./main.o ./main.cpp It outputs this errors: ./main.cpp: In function ‘int main()’: ./main.cpp:13:43: error: ‘printf’ was not declared in this scope radek@mypc:~> nano main.cpp radek@mypc:~> g++ -pedantic -g -O1 -o ./main.o ./main.cpp /tmp/cc0g3GUE.o: In function `basic_regex': /usr/include/c++/4.5/tr1_impl/regex:771: undefined reference to `std::tr1::basic_regex<char, std::tr1::regex_traits<char> >::_M_compile()' /tmp/cc0g3GUE.o: In function `bool std::tr1::regex_match<char const*, char, std::tr1::regex_traits<char> >(char const*, char const*, std::tr1::basic_regex<char, std::tr1::regex_traits<char> > const&, std::bitset<11u>)': /usr/include/c++/4.5/tr1_impl/regex:2144: undefined reference to `bool std::tr1::regex_match<char const*, std::allocator<std::tr1::sub_match<char const*> >, char, std::tr1::regex_traits<char> >(char const*, char const*, std::tr1::match_results<char const*, std::allocator<std::tr1::sub_match<char const*> > >&, std::tr1::basic_regex<char, std::tr1::regex_traits<char> > const&, std::bitset<11u>)' collect2: ld returned 1 exit status What packages should i (un)install to make the code work on my PC?

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• How does the ? make a quantifier lazy in regex

  - by Uriel Katz

  I've been looking into regex lately and figured that the ? operator makes the *,+, or ? lazy. My question is how does it do that? Is it that *? for example is a special operator, or does the ? have an effect on the *? In other words, does regex recognize *? as one operator in itself, or does regex recognize *? as the two separate operators * and ?? If it is the case that *? is being recognized as two separate operators, how does the ? affect the * to make it lazy. If ? means that the * is optional, shouldn't this mean that the * doesn't have to exists at all. If so, then in a statement .*? wouldn't regex just match separate letters and the whole string instead of the shorter string? Please explain, I'm desperate to understand.

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• Regex: how to get contents from tag inner (use javascript)?

  - by lazyanno

  page contents: aa<b>1;2'3</b>hh<b>aaa</b>.. .<b>bbb</b> blabla.. i want to get result: 1;2'3aaabbb match tag is <b> and </b> how to write this regex using javascript? thanks!

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• codingbat wordEnds using regex

  - by polygenelubricants

  I'm trying to solve wordEnds from codingbat.com using regex. This is the simplest as I can make it with my current knowledge of regex: public String wordEnds(String str, String word) { return str.replaceAll( String.format( ".*?(?=%s)(?<=(.|^))%1$s(?=(.|$))|.+", java.util.regex.Pattern.quote(word) ), "$1$2" ); } String.format is used to inject word into the pattern for both readability and convenience (it's injected twice). Pattern.quote isn't necessary to pass their tests, but I think it's required for a proper regex-based solution. The regex has two major parts: If after matching as few characters as possible ".*?", word can still be found "(?=%s)", then lookbehind to capture any character immediately preceding it "(?<=(.|^))", match word "%1$s" and lookforward to capture any character following it "(?=(.|$))". The initial "if" test ensures that the atomic lookbehind captures only if there's a word Using lookahead to capture the following character doesn't consume it, so it can be used as part of further matching Otherwise match what's left "|.+" Groups 1 and 2 would capture empty strings I think this works in all cases, but it's obviously quite complex. I'm just wondering if others can suggest a simpler regex to do this. Note: I'm not looking for a solution using indexOf and a loop. I want a regex-based replaceAll solution. I also need a working solution that I can just copy-paste into codingbat and passes.

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• Regex pattern failing

  - by Scott Chamberlain

  I am trying a substring to find from the beginning of the string to the point that has the escape sequence "\r\n\r\n" my regex is Regex completeCall = new Regex(@"^.+?\r\n\r\n", RegexOptions.Compiled); it works great as long as you only have strings like 123\r\n\r\n however once you have the pattern 123\r\n 456\r\n\r\n the pattern no longer matches. Any advice on what I am doing wrong? Regex completeCall = new Regex(@"^.+?\r\n\r\n", RegexOptions.Compiled); Regex junkLine = new Regex(@"^\D", RegexOptions.Compiled); private void ClientThread() { StringBuilder stringBuffer = new StringBuilder(); (...) while(true) { (...) Match match = completeCall.Match(stringBuffer.ToString()); while (Match.Success) //once stringBuffer has somthing like "123\r\n 456\r\n\r\n" Match.Success always returns false. { if (junkLine.IsMatch(match.Value)) { (...) } else { (...) } stringBuffer.Remove(0, match.Length); // remove the processed string match = completeCall.Match(stringBuffer.ToString()); // check to see if more than 1 call happened while the thread was sleeping. } Thread.Sleep(1000); }

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• Nested Groups in Regex

  - by cryptic-star

  I'm constructing a regex that is looking for dates. I would like to return the date found and the sentence it was found in. In the code below, the strings on either side of date_string should check for the conditions of a sentence. For your sake, I've omitted the regex for date_string - sufficed to say, it works for picking out dates. While the inside of date_string isn't important, it is grouped as one entire regex. "((?:[^.|?|!]*)"+date_string+"(?:[^.|?|!]*[.|?|!]\s*))" The problem is that date_string is only matching the last number of any given date, presumably because the regex in front of date_string is matching too far and overrunning the date regex. For example, if I say "Independence Day is July 4.", I will get the sentence and 4, even though it should match 'July 4'. In case you're wondering, my regex inside date_string are ordered in such a way that 'July 4' should match first. Is there any way to do this all in one regex? Or do I need to split it up somehow (i.e. split up all text into sentences, and then check each sentence)?

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• Regex | validation error

  - by MMRUser

  I'm trying to validate a USA mobile number, since I'm using pre-built javascript validation library I just replaced this regex validation with the previous one which comes with the validation library. previous validation regex: "telephone":{ "regex":"/^[0-9\-\(\)\ ]{10,10}$/", "alertText":"* Invalid phone number"}, This works like 2126661234 but not in USA standard. After I changed: "telephone":{ "regex":"/^[2-9]\d{2}-\d{3}-\d{4}$/", "alertText":"* Invalid phone number"}, Now every entry I get an error even if I enter 212-666-1234 I really don't know what is the wrong, so I'm expecting some help.

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