I have a Regex that I now need to moved into C#. I'm getting errors like this
Unrecognized escape sequence
I am using Regex.Escape -- but obviously incorrectly.
string pattern = Regex.Escape("^.*(?=.{7,})(?=.*[a-zA-Z])(?=.*(\d|[!##$%\?\(\)\*\&\^\-\+\=_])).*$");
hiddenRegex.Attributes.Add("value", pattern);
How is this correctly done?
The error you're getting is coming at compile time correct? That means C# compiler is not able to make sense of your string. Prepend # sign before the string and you should be fine. You don't need Regex.Escape.
See What's the # in front of a string in C#?
var pattern = new Regex(#"^.*(?=.{7,})(?=.*[a-zA-Z])(?=.*(\d|[!##$%\?\(\)\*\&\^\-\+\=_])).*$");
pattern.IsMatch("Your input string to test the pattern against");
The error you are getting is due to the fact that your string contains invalid escape sequences (e.g. \d). To fix this, either escape the backslashes manually or write a verbatim string literal instead:
string pattern = #"^.*(?=.{7,})(?=.*[a-zA-Z])(?=.*(\d|[!##$%\?\(\)\*\&\^\-\+\=_])).*$";
Regex.Escape would be used when you want to embed dynamic content to a regular expression, not when you want to construct a fixed regex. For example, you would use it here:
string name = "this comes from user input";
string pattern = string.Format("^{0}$", Regex.Escape(name));
You do this because name could very well include characters that have special meaning in a regex, such as dots or parentheses. When name is hardcoded (as in your example) you can escape those characters manually.
Related
I'm writing a program in C# using Microsoft Visual Studio, i need the program to match the vertical bar, but when I try to escape it like this "\|" it gives me an unrecognized escape sequence error. What am I doing wrong?
In C#
string test = "\|";
Is going to fail because this is a C# string escape sequence, and no such escape exists. Because you are trying to include a backslash in the string, you need to escape the slash so the string actually contains a slash:
string test = "\\|";
What will actually be stored in this string is \|
The reason you get an unrecognized escape sequence is that backslash is used as an escape character in C# string literals as well as in regex.
You have several choices to fix this:
Use verbatim literals, i.e. #"\|", or
Use a second escape inside a regular literal, i.e. "\\|", or
Use a character class, i.e. [|]
The third one is my personal favorite, because it does not require counting backslashes.
The string is treating "\|" as an escaped pipe in C#. Try "\|" to escape the \ so that the regex actually sees the \| you want.
I am trying to search a for a specific string in an HTML file. The string I am looking for is
HHA_HG
If I use notepad I can see that the string only exists once in the file.
However
MatchCollection matches = Regex.Matches(inputString, "HHA_HG");
Returns no matches. I verify the inputString contains the string I want.
The weird thing is if I remove all the lines apart from the line containing HHA_HG I can get a match. If I just search for HHA_ in the full file I can get matches although none of the matches are HHA_HG.
Does the underscore mean something special?
No, it does not. That should be fine. Possible explanation: is there an invisible unicode character in either the source or regex pattern? Or alternative "looks like an A but isn't an A" unicode characters? Basically, what are the actual char values in both the regex pattern and the file (at the appropriate location)? Is the HHA_HG in the file actually in a RTL block, and is actually GH_AHH ?
I have following Regex on C# and its causing Error: C# Unrecognized escape sequence on \w \. \/ .
string reg = "<a href=\"[\w\.\/:]+\" target=\"_blank\">.?<img src=\"(?<imgurl>\w\.\/:])+\"";
Regex regex = new Regex(reg);
I also tried
string reg = #"<a href="[w./:]+" target=\"_blank\">.?<img src="(?<imgurl>w./:])+"";
But this way the string "ends" at href=" "-char
Can anyone help me please?
Use "" to escape quotations when using the # literal.
There are two escaping mechanisms at work here, and they interfere. For example, you use \" to tell C# to escape the following double quote, but you also use \w to tell the regular expression parser to treat the following W special. But C# thinks \w is meant for C#, doesn't understand it, and you get a compiler error.
For example take this example text:
<a href="file://C:\Test\Test2\[\w\.\/:]+">
There are two ways to escape it such that C# accepts it.
One way is to escape all characters that are special to C#. In this case the " is used to denote the end of the string, and \ denotes a C# escape sequence. Both need to be prefixed with a C# escape \ to escape them:
string s = "<a href=\"file://C:\\Test\\Test2\\[\\w\\.\\/:]+\">";
But this often leads to ugly strings, especially when used with paths or regular expressions.
The other way is to prefix the string with # and escape only the " by replacing them with "":
string s = #"<a href=""file://C:\Test\Test2\[\w\.\/:]+"">";
The # will prevent C# from trying to interpret the \ in the string as escape characters, but since \" will not be recognized then either, they invented the "" to escape the double quote.
Here's a better regex, yours is filled with problems:
string reg = #"<a href=""[\w./:]+"" target=""_blank"">.?<img src=""(?<imgurl>[\w./:]+)""";
Regex regex = new Regex(reg);
var m = regex.Match(#"http://www.yahoo.com""
target=""_blank"">http://flickr.com/something.jpg""");
Catches <a href="http://www.yahoo.com" target="_blank"><img src="http://flickr.com/something.jpg".
Problems with yours: Forward slashes don't need to be escaped, missing the [ bracket in the img part, putting the ) in the right position in the closing of the group.
However, as has been said many times, HTML is not structured enough to be caught by regex. But if you need to get something quick and dirty done, it will do.
Here's the deal. C# Strings recognize certain character combinations as specific special characters to manipulate strings. Maybe you are familiar with inserting a \n in a string to work as and End of Line character, for example?
When you put a single \ in a string, it will try to verify it, along with the next character, as one of these special commands, and will throw an error when its not a valid combination.
Fortunately, that does not prevent you from using backslashes, as one of those sequences, \\, works for that purpose, being interpreted as a single backslash.
So, in practice, if you substitute every backslash in your string for a double backslash, it should work properly.
I was using Regex and I tried to write:
Regex RegObj2 = new Regex("\w[a][b][(c|d)][(c|d)].\w");
Gives me this error twice, one for each appearance of \w:
unrecognized escape sequence
What am I doing wrong?
You are not escaping the \s in a non-verbatim string literal.
Solution: put a # in front of the string or double the backslashes, as per the C# rules for string literals.
Try to escape the escape ;)
Regex RegObj2 = new Regex("\\w[a][b][(c|d)][(c|d)].\\w");
or add a # (as #Dominic Kexel suggested)
There are two levels of potential escaping required when writing a regular expression:
The regular expression escaping (e.g. escaping brackets, or in this case specifying a character class)
The C# string literal escaping
In this case, it's the latter which is tripping you up. Either escape the \ so that it becomes part of the string, or use a verbatim string literal (with an # prefix) so that \ doesn't have its normal escaping meaning. So either of these:
Regex regex1 = new Regex(#"\w[a][b][(c|d)][(c|d)].\w");
Regex regex2 = new Regex("\\w[a][b][(c|d)][(c|d)].\\w");
The two approaches are absolutely equivalent at execution time. In both cases you're trying to create a string constant with the value
\w[a][b][(c|d)][(c|d)].\w
The two forms are just different ways of expressing this in C# source code.
The backslashes are not being escaped e.g. \\ or
new Regex(#"\w[a][b][(c|d)][(c|d)].\w");
How i can use "/show_name=(.?)&show_name_exact=true\">(.?)
Match m = Regex.Match(input, "/show_name=(.*?)&show_name_exact=true\">(.*?)</i", RegexOptions.IgnoreCase);
// Check Match instance
if (m.Success)
{
// Get Group value
string key = m.Groups[1].Value;
Console.WriteLine(key);
// alternate-1
}
Error, Unterminated string literal(CS1039)]
Error, Newline in constant(CS1010)]
What I am doing wrong?
I think you're mixing up .NET's regex syntax with PHP's. PHP requires you to use a regex delimiter in addition to the quotes that are required by the C# string literal. For instance, if you want to match "foo" case-insensitively in PHP you would use something like this:
'/foo/i'
...but C# doesn't require the extra regex delimiters, which means it doesn't support the /i style for adding match modifiers (that would have been redundant anyway, since you're also using the RegexOptions.IgnoreCase flag). I think this is what you're looking for:
#"show_name=(.*?)&show_name_exact=true"">(.*?)<"
Note also how I escaped the internal quotation mark using another quotation mark instead of a backslash. You have to do it that way whether you use the old-fashioned string literal syntax or C#'s verbatim strings with the leading '#' (which is highly recommended for writing regexes). That's why you were getting the unterminated string error.