I haven't been able to find anything online regarding this. There's RegexOptions, but it doesn't have Global as one of its options. The inline modifiers list also doesn't mention global matching.
In a nutshell, I've got a regex to parse something like
--arga= "arg1" --argb ="arg2"
into separate argument name/value pairs using this regex:
--(\\w+)\\s*=\\s*\"(\\w+)\"\\s*
but the .NET Regex class doesn't do it globally (iteratively). So in order for me to get this to work, I'd have to do a match, then remove this from the argument string, and loop over and over again until I've exhausted all of the arguments.
It would be nicer to run the regex once, and then loop over the match groups to get the name value pairs. Is this possible? What am I missing?
You're looking for the Regex.Matches method (plural), which returns a collection containing all of the matches in the original string.
Related
Say I have a regex matching a hexadecimal 32 bit number:
([0-9a-fA-F]{1,8})
When I construct a regex where I need to match this multiple times, e.g.
(?<from>[0-9a-fA-F]{1,8})\s*:\s*(?<to>[0-9a-fA-F]{1,8})
Do I have to repeat the subexpression definition every time, or is there a way to "name and reuse" it?
I'd imagine something like (warning, invented syntax!)
(?<from>{hexnum=[0-9a-fA-F]{1,8}})\s*:\s*(?<to>{=hexnum})
where hexnum= would define the subexpression "hexnum", and {=hexnum} would reuse it.
Since I already learnt it matters: I'm using .NET's System.Text.RegularExpressions.Regex, but a general answer would be interesting, too.
RegEx Subroutines
When you want to use a sub-expression multiple times without rewriting it, you can group it then call it as a subroutine. Subroutines may be called by name, index, or relative position.
Subroutines are supported by PCRE, Perl, Ruby, PHP, Delphi, R, and others. Unfortunately, the .NET Framework is lacking, but there are some PCRE libraries for .NET that you can use instead (such as https://github.com/ltrzesniewski/pcre-net).
Syntax
Here's how subroutines work: let's say you have a sub-expression [abc] that you want to repeat three times in a row.
Standard RegEx
Any: [abc][abc][abc]
Subroutine, by Name
Perl: (?'name'[abc])(?&name)(?&name)
PCRE: (?P<name>[abc])(?P>name)(?P>name)
Ruby: (?<name>[abc])\g<name>\g<name>
Subroutine, by Index
Perl/PCRE: ([abc])(?1)(?1)
Ruby: ([abc])\g<1>\g<1>
Subroutine, by Relative Position
Perl: ([abc])(?-1)(?-1)
PCRE: ([abc])(?-1)(?-1)
Ruby: ([abc])\g<-1>\g<-1>
Subroutine, Predefined
This defines a subroutine without executing it.
Perl/PCRE: (?(DEFINE)(?'name'[abc]))(?P>name)(?P>name)(?P>name)
Examples
Matches a valid IPv4 address string, from 0.0.0.0 to 255.255.255.255:
((?:25[0-5])|(?:2[0-4][0-9])|(?:[0-1]?[0-9]?[0-9]))\.(?1)\.(?1)\.(?1)
Without subroutines:
((?:25[0-5])|(?:2[0-4][0-9])|(?:[0-1]?[0-9]?[0-9]))\.((?:25[0-5])|(?:2[0-4][0-9])|(?:[0-1]?[0-9]?[0-9]))\.((?:25[0-5])|(?:2[0-4][0-9])|(?:[0-1]?[0-9]?[0-9]))\.((?:25[0-5])|(?:2[0-4][0-9])|(?:[0-1]?[0-9]?[0-9]))
And to solve the original posted problem:
(?<from>(?P<hexnum>[0-9a-fA-F]{1,8}))\s*:\s*(?<to>(?P>hexnum))
More Info
http://regular-expressions.info/subroutine.html
http://regex101.com/
Why not do something like this, not really shorter but a bit more maintainable.
String.Format("(?<from>{0})\s*:\s*(?<to>{0})", "[0-9a-zA-Z]{1,8}");
If you want more self documenting code i would assign the number regex string to a properly named const variable.
.NET regex does not support pattern recursion, and if you can use (?<from>(?<hex>[0-9a-fA-F]{1,8}))\s*:\s*(?<to>(\g<hex>)) in Ruby and PHP/PCRE (where hex is a "technical" named capturing group whose name should not occur in the main pattern), in .NET, you may just define the block(s) as separate variables, and then use them to build a dynamic pattern.
Starting with C#6, you may use an interpolated string literal that looks very much like a PCRE/Onigmo subpattern recursion, but is actually cleaner and has no potential bottleneck when the group is named identically to the "technical" capturing group:
C# demo:
using System;
using System.Text.RegularExpressions;
public class Test
{
public static void Main()
{
var block = "[0-9a-fA-F]{1,8}";
var pattern = $#"(?<from>{block})\s*:\s*(?<to>{block})";
Console.WriteLine(Regex.IsMatch("12345678 :87654321", pattern));
}
}
The $#"..." is a verbatim interpolated string literal, where escape sequences are treated as combinations of a literal backslash and a char after it. Make sure to define literal { with {{ and } with }} (e.g. $#"(?:{block}){{5}}" to repeat a block 5 times).
For older C# versions, use string.Format:
var pattern = string.Format(#"(?<from>{0})\s*:\s*(?<to>{0})", block);
as is suggested in Mattias's answer.
If I am understanding your question correctly, you want to reuse certain patterns to construct a bigger pattern?
string f = #"fc\d+/";
string e = #"\d+";
Regex regexObj = new Regex(f+e);
Other than this, using backreferences will only help if you are trying to match the exact same string that you have previously matched somewhere in your regex.
e.g.
/\b([a-z])\w+\1\b/
Will only match : text, spaces in the above text :
This is a sample text which is not the title since it does not end with 2 spaces.
There is no such predefined class. I think you can simplify it using ignore-case option, e.g.:
(?i)(?<from>[0-9a-z]{1,8})\s*:\s*(?<to>[0-9a-z]{1,8})
To reuse regex named capture group use this syntax: \k<name> or \k'name'
So the answer is:
(?<from>[0-9a-fA-F]{1,8})\s*:\s*\k<from>
More info: http://www.regular-expressions.info/named.html
I need to extract a series of meaningful values from a file. The basic pattern for the values I need to match looks like:
"indicator\..+?"\[true\]
Unfortunately, in places this is spanning across quite a bit of content to get a true match, and the lazy quantifier (?) is not being as lazy as I'd like.
How do I modify the above so that out of the following:
"indicator.value here"[false],"other content","more other
content","indicator don't match this one because the full stop is missing"[true],"indicator.this is the
value I want matched"[true]
only this value is returned: "indicator.this is the value I want matched"[true]
Currently, that whole string is being returned by my above regex.
Assuming commas are the delimiter - simply avoid matching on them:
#"""indicator\.[^,]+?""\[true\]"
Try using "indicator\.(.*)?"\[true\] instead and see if that helps. I think the lazy only applies to the * operator. I vaguely remember having this issue years ago.
You can leverage the discard technique by discarding the pattern you don't want. So, you could have something like this:
"indicator\..+?"\[false\]|"indicator\.(.+?)"\[true\]
Discard this pattern --^ Capture this --^
Working demo
Match information
MATCH 1
1. [150-182] `this is the value I want matched`
Background
I am trying to do some regex matching and replacing, but for some reason the replacement isn't correct in .NET.
Regex pattern - "^.*?/rebate/?$"
Input string - "/my-tax/rebate"
Replacement string - "/new-path/rebate"
Basically, if the word 'rebate' is seen in a string, the input string needs to be replaced entirely by the replacement string.
Problem
If I create a regex with the pattern and execute
patternMatch.Pattern.Replace("/my-tax/rebate", "/new-path/rebate")
I get /my-tax/new-path/rebate, which isn't correct.
But, if I execute -
new Regex(#"^.*?/rebate/?$").Replace("/my-tax/rebate", "/new-path/rebate"),
the result is correct - /new-path/rebate
Why is that?
patternMatch is an object with two properties - one Pattern (which is the Regex Pattern) and another one is TargetPath (which is the replacement string). In this example, I am only using the pattern property.
patternMatch.Pattern on debugging is
Here are the results during run time-
You are simply wrongly using the function. I'm not sure how you are getting /my-tax/new-path/rebate since it is giving me an error on ideone.com (Maybe you have a regex named Pattern?).
Anyway, you shouldn't have any issues with using the function like this:
patternMatch.Replace("/my-tax/rebate", "/new-path/rebate");
ideone demo
A number of points in your question are incorrect. The regex is replacing correctly.
Per #XiaoguangQiao's comment, what is patternMatch.Pattern.Replace? Your example...
var patternMatch = new Regex("^.*?/rebate/?$");
patternMatch.Pattern.Replace("/my-tax/rebate", "/new-path/rebate");
...errors with the message...
'System.Text.RegularExpressions.Regex' does not contain a definition for 'Pattern' and no extension method 'Pattern' accepting a first argument of type 'System.Text.RegularExpressions.Regex' could be found
...when I throw it into a quick LINQPad 4 query (set to C# Statement(s)).
pattern is a private string field of System.Text.RegularExpressions.Regex; and patternMatch.Replace("/my-tax/rebate", "/new-path/rebate") - which I expect is what you meant - yields the correct result ("/new-path/rebate") rather than the incorrect result you said you get ("/my-tax/new-path/rebate").
Otherwise your pattern(s) (i.e. with and without the extra / that #rene pointed out) is fine for the input ("/my-tax/rebate") and replacement ("/new-path/rebate") you initially outline - insofar as they match and yield the result you want. You can check this outside your code in quick fiddles with the extra / and without the extra /.
Use String.Replace Method.
str.replace("rebate","new-path/rebate")
http://msdn.microsoft.com/en-us/library/fk49wtc1%28v=vs.110%29.aspx
I want to validate a URL using regular expression. Following are my conditions to validate the URL:
Scheme is optional
Subdomains should be allowed
Port number should be allowed
Path should be allowed.
I was trying the following pattern:
((http|https)://)?([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?
But I am not getting the desired results. Even an invalid URL like '*.example.com' is getting matched.
What is wrong with it?
are you matching the entire string? you don't say what language you are using, but in python it looks like you may be using search instead of match.
one way to fix this is to start you regexp with ^ and end it with $.
While parsing URL's is best left to a library (since I know perl best, I would suggest something like http://search.cpan.org/dist/URI/), if you want some help debugging that statement, it might be best to try it in a debugger, something like: http://www.debuggex.com/.
I think one of the main reasons it is matching, is because you don't use beginning and ending string match markers. Meaning, no part of that string might be matching what you put in explicitly, but because you haven't marked it with beginning and end markers for the string, your regex could just be matching 'example.com' in your string, not the entire input.
Found the regular expression for my condition with help from your inputs
^(http(s)?://)?[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*(:(0-9)*)*(\/?)([a-zA-Z0-9\-\.\?\,\'\/\\\+&%\$#_]*)?$
Following code works for me in c#
private static bool IsValidUrl(string url)
{
return new Regex(#"^(http|http(s)?://)?([\w-]+\.)+[\w-]+[.\w]+(\[\?%&=]*)?").IsMatch(url) &&!new Regex(#"[^a-zA-Z0-9]+$").IsMatch(url);
}
it allows "something.anything (at least 2 later after period) with or without http(s) and www.
I have a list like :
george fg
michel fgu
yasser fguh
I would like to replace fg, fgu, and fguh by "fguhCool" I already tried something like this :
foreach (var ignore in NameToPoulate)
{
tempo = ignore.Replace("fg", "fguhCool");
NameToPoulate_t.Add(tempo);
}
But then "fgu" become "fguhCoolu" and "fguh" become "fguhCooluh" is there are a better idea ?
Thanks for your help.
I assume that this is a homework assignment and that you are being tested for the specific algorihm rather than any code that does the job.
This is probably what your teacher has in mind:
Students will realize that the code should check for "fguh" first, then "fgu" then "fg". The order is important because replacing "fg" will, as you have noticed, destroy a "fguh".
This will by some students be implemented as a loop with if-else conditions in them. So that you will not replace a "fg" that is within an already replaced "fguhCool".
But then you will find that the algorithm breaks down if "fg" and "fgu" are both within the same string. You cannot then allow the presence of "fgu" prevent you to check for "fg" at a different part of the string.
The answer that your teacher is looking for is probably that you should first locate "fguh", "fgu" and "fg" (in that order) and replace them with an intermediary string that doesn't contain "fg". Then after you have done that, you can search for that intermediary string and replace it with "fguhCool".
You could use regular expressions:
Regex.Replace(#"\bfg\b", "fguhCool");
The \b matches a so-called word boundary which means it matches the beginnnig or end of a word (roughly, but for this purpose enough).
Use a regular expression:
Regex.Replace("fg(uh?)?", "fguhCool");
An alternative would be replacing the long words for the short ones first, then replacing the short for the end value (I'm assuming all words - "fg", "fgu" and "fguh" - would map to the same value "fguhCool", right?)
tempo = ignore
.Replace("fguh", "fg")
.Replace("fgu", "fg")
.Replace("fg", "fguhCool");
Obs.: That assumes those words can appear anywhere in the string. If you're worried about whole words (i.e. cases where those words are not substrings of a bigger word), then see #Joey's answer (in this case, simple substitutions won't do, regexes are really the best option).