I have the following Regex in C#:
Regex h1Separator = new Regex(#"<h1>(?'name'[\w\d\s]+?)(<br\s?/?>)?</h1>", RegexOptions.Singleline);
Trying to match a string that looks like this:
<h1>test content<br>
</h1>
right now it matches strings that look like the following:
<h1>test content<br></h1>
<h1>test content</h1>
What am I doing wrong? Should I be matching for a newline character? If so, what is it in C#? I can't find one.
You don't check for whitespace between the end of the br tag and the start of the next tag, so it expects to see the hr tag immediately after. Add a \s* in between to allow that.
You have it defined as a single line regex, see the RegexOptions.Singleline flag :) use RegexOptions.Multiline
The newline character in C# is: \n. However, I am not skilled in regex and couldn't tell you what would happen if there was a newline in a regex expression.
you can either add a dot . to your string before the ending </h1> and keep the RegexOptions.Singleline option, or change it to RegexOptions.Multiline and add a $ to the regex before the </h1>. details here
Use the Multiline flag. (Edit to address my mispeaking about the .Net platform).
Singleline mode treats the entire string you are passing in as one entry. Therefore ^ and $ represent the entire string and not the beginning and ending of a line within the string. Example <h1>(?'name'[\w\d\s]+?)(<br\s?/?>)?</h1> will match this:
<h1>test content<br></h1>
Multiline mode changes the meaning of ^ and $ to the beginning and ending of each line within the string (i.e. they will look at every line break).
Regex h1Separator = new Regex(#"<h1>(?'name'[\w\d\s]+?)$(<br\s?/?>)?</h1>", RegexOptions.Multiline);
will match the desired pattern:
<h1>test content<br>
</h1>
In short, you need to tell the regex parser you expect to work with multiple lines. It helps to have a regex designer that speaks your dialect of regex. There are many.
Related
I'm trying to highlight markdown code, but am running into this weird behavior of the .NET regex multiline option.
The following expression: ^(#+).+$ works fine on any online regex testing tool:
But it refuses to work with .net:
It doesn't seem to take into account the $ tag, and just highlights everything until the end of the string, no matter what. This is my C#
RegExpression = new Regex(#"^(#+).+$", RegexOptions.Multiline)
What am I missing?
It is clear your text contains a linebreak other than LF. In .NET regex, a dot matches any char but LF (a newline char, \n).
See Multiline Mode MSDN regex reference
By default, $ matches only the end of the input string. If you specify the RegexOptions.Multiline option, it matches either the newline character (\n) or the end of the input string. It does not, however, match the carriage return/line feed character combination. To successfully match them, use the subexpression \r?$ instead of just $.
So, use
#"^(#+).+?\r?$"
The .+?\r?$ will match lazily any one or more chars other than LF up to the first CR (that is optional) right before a newline.
Or just use a negated character class:
#"^(#+)[^\r\n]+"
The [^\r\n]+ will match one or more chars other than CR/LF.
What you have is good. The only thing you're missing is that . doesn't match newline characters, even with the multiline option. You can get around this in two different ways.
The easiest is to use the RegexOptions.Singleline flag which cause newlines to be treated as characters. That way, ^ still matches the start of the string, $ matches the end of the string and . matches everything including newlines.
The other way to fix this (although I wouldn't recomend it for your use case) is to modify your regex to explicitly allow newlines. To do this you can just replace any . with (?:.|\n) which means either anycharacter or a newline. For your example, you would end up with ^(#+)(?:.|\n)+$. If you want to ensure that there's a non-linebreak character first, add an extra dot: ^(#+).(?:.|\n)+$
I have this string
string s = "<textarea>\r\n</textarea>";
And I want to replace the textarea content dynamically, trying it like this:
Regex regex = new Regex("(<textarea.*?>)(.*)(</textarea>)");
string a = regex.Replace(s, "$1new value$3");
Yet this does not procedure the output I want, which should be: <textarea>new value</textarea>. It just produces
<textarea>
</textarea>
How can I fix it?
Use RegexOptions.SingleLine mode. Otherwise . does not match newlines.
According to the documentation:
Singleline Specifies single-line mode. Changes the meaning of the dot
(.) so it matches every character (instead of every character except
\n).
.* will stop when it encounters a \n.
So use RegexOptions.MultiLine option.
Or just change your regex to:
(?m)(<textarea.*?>)(.*)(</textarea>)
(?m) is inline multiline modifier.
Edit:
Sorry It should've been RegexOptions.SingleLine. I was confused since I use regex only in javascript on a large basis.
How would a regex pattern to match each line of a given text be?
I'm trying ^(.+)$ but it includes crlf...
Just use RegexOptions.Multiline.
Multiline mode. Changes the meaning of
^ and $ so they match at the beginning
and end, respectively, of any line,
and not just the beginning and end of
the entire string.
Example:
var lineMatches = Regex.Matches("Multi\r\nlines", "^(.+)$", RegexOptions.Multiline);
I'm not sure what you mean by "match each line of a given text" means, but you can use a character class to exclude the CR and LF characters:
[^\r\n]+
The wording of your question seems a little unclear, but it sounds like you want RegexOptions.Multiline (in the System.Text.RegularExpressions namespace). It's an option you have to set on your RegEx object. That should make ^ and $ match the beginning and end of a line rather than the entire string.
For example:
Regex re = new Regex("^(.+)$", RegexOptions.Compiled | RegexOptions.Multiline);
Have you tried:
^(.+)\r?\n$
That way the match group includes everything except the CRLF, and requires that a new line be present (Unix default), but accepts the carriage return in front (Windows default).
I assume you're using the Multiline option? In that case you'll want to match the newline explicitly with "\n". (substitute "\r\n" as appropriate.)
If I use this
string showPattern = #"return new_lightox\(this\);"">[a-zA-Z0-9(\s),!\?\-:'&%]+</a>";
MatchCollection showMatches = Regex.Matches(pageSource, showPattern);
I get some matches but I want to get rid of [a-zA-Z0-9(\s),!\?\-:'&%]+and use any char .+
but if do this I get no match at all.
What am I doing wrong?
By default "." does not match newlines, but the class \s does.
To let . match newline, turn on SingleLine/DOTALL mode - either using a flag in the function call (as Abel's answer shows), or using the inline modifier (?s), like this for the whole expression:
"(?s)return new_lightox\(this\);"">.+</a>"
Or for just the specific part of it:
"return new_lightox\(this\);"">(?s:.+)</a>"
It might be better to take that a step further and do this:
"return new_lightox\(this\);"">(?s:(?!</?a).+)</a>"
Which should prevent the closing </a> from belonging to a different link.
However, you need to be very wary here - it's not clear what you're doing overall, but regex is not a good tool for parsing HTML with, and can cause all sorts of problems. Look at using a HTML DOM parser instead, such as HtmlAgilityPack.
You're matching a tag, so you probably want something along these lines, instead of .+:
string showPattern = #"return new_lightox\(this\);"">[^<]+</a>";
The reason that the match doesn't hit is possibly because you are missing the multiline/singleline flag and the closing tag is on the next line. In other words, this should work too:
// SingleLine option changes the dot (.) to match newlines too
MatchCollection showMatches = Regex.Matches(
pageSource,
showPattern,
RegexOptions.SingleLine);
I am trying to make a regex that matches all occurrences of words that are at the start of a line and begin with #.
For example in:
#region #like
#hey
It would match #region and #hey.
This is what I have right now:
^#\w*
I apologize for posting this question. I'm sure it has a very simple answer, but I have been unable to find it. I admit that I am a regex noob.
What you've got should work, depending on what flags you pass for RegexOptions. You need to make sure you pass RegexOptions.Multiline:
var matches = Regex.Matches(input, #"^#\w*", RegexOptions.Multiline);
See the documentation I linked to above:
Multiline Multiline mode. Changes the meaning of ^ and $ so they match at the beginning and end, respectively, of any line, and not just the beginning and end of the entire string.
The regex looks fine, make sure you're using a verbatim string literal (# prefix) to define your regex, i.e. #"^#\w*" otherwise the backslash will be treated as an escape sequence.
Use this regex
^#.+?\b
.+ will ensure at least one character after # and \b indicates word boundry. ? adds non-greediness to the + operator so as to avoid matching whole string #region #like