Greetings, I have file with the following strings:
string.Format("{0},{1}", "Having \"Two\" On The Same Line".Localize(), "Is Tricky For regex".Localize());
my goal is to get a match set with the two strings:
Having \"Two\" On The Same Line
Is Tricky For regex
My current regex looks like this:
private Regex CSharpShortRegex = new Regex("\"(?<constant>[^\"]+?)\".Localize\\(\\)");
My problem is with the escaped quotes in the first line I end up stopping at the quote and I get:
On The Same Line
Is Tricky For This Style Too
however attempting to ignore the escaped quotes is not working out because it makes the Regex greedy and I get
Having \"Two\" On The Same Line".Localize(), "Is Tricky For regex"
We seem to be caught between maximum and minimum munge. Is there any hope? I have some backup plans. Can you Regex backwards? that would make it easier because I can start with the "()ezilacoL."
EDIT:
To clarify. This is my lone edge case. Most of the time the string sits alone like:
var myString = "Hot Patootie".Localize()
This one works for me:
\"((?:[^\\"]|(?:\\\"))*)\"\.Localize\(\)
Tested on http://www.regexplanet.com/simple/index.html against a number of strings with various escaped quotes.
Looks like most of us who answered this one had the same rough idea, so let me explain the approach (comments after #s):
\" # We're looking for a string delimited by quotation marks
( # Capture the contents of the quotation marks
(?: # Start a non-capturing group
[^\\"] # Either read a character that isn't a quote or a slash
|(?:\\\") # Or read in a slash followed by a quote.
)* # Keep reading
) # End the capturing group
\" # The string literal ends in a quotation mark
\.Localize\(\) # and ends with the literal '.Localize()', escaping ., ( and )
For C# you'll need to escape the slashes twice (messy):
\"((?:[^\\\\\"]|(?:\\\\\"))*)\"\\.Localize\\(\\)
Mark correctly points out that this one doesn't match escaped characters other than quotation marks. So here's a better version:
\"((?:[^\\"]|(?:\\")|(?:\\.))*)\"\.Localize\(\)
And its slashed-up equivalent:
\"((?:[^\\\\\"]|(?:\\\\\")|(?:\\\\.))*)\"\\.Localize\\(\\)
Works the same way, except it has a special case that if encounters a slash but it can't match \", it just consumes the slash and the following character and moves on.
Thinking about it, it's better to just consume two characters at every slash, which is effectively Mark's answer so I won't repeat it.
Here's the regular expression you need:
#"""(?<constant>(\\.|[^""])*)""\.Localize\(\)"
A test program:
using System;
using System.Text.RegularExpressions;
using System.IO;
class Program
{
static void Main()
{
Regex CSharpShortRegex =
new Regex(#"""(?<constant>(\\.|[^""])*)""\.Localize\(\)");
foreach (string line in File.ReadAllLines("input.txt"))
foreach (Match match in CSharpShortRegex.Matches(line))
Console.WriteLine(match.Groups["constant"].Value);
}
}
Output:
Having \"Two\" On The Same Line
Is Tricky For regex
Hot Patootie
Notice that I have used #"..." to avoid having to escape backslashes inside the regular expression. I think this makes it easier to read.
Update:
My original answer (below the horizontal rule) has a bug: regular-expression matchers attempt alternatives in left-to-right order. Having [^"] as the first alternative allows it to consume the backslash, but then the next character to be matched is a quote, which prevents the match from proceeding.
Incompatibility note: Given the pattern below, perl backtracks to the other alternative (the escaped quote) and successfully finds a match for the Having \"Two\" On The Same Line case.
The fix is to try an escaped quote first and then a non-quote:
var CSharpShortRegex =
new Regex("\"(?<constant>(\\\\\"|[^\"])*)\"\\.Localize\\(\\)");
or if you prefer the at-string form:
var CSharpShortRegex =
new Regex(#"""(?<constant>(\\""|[^""])*)""\.Localize\(\)");
Allow for escapes:
private Regex CSharpShortRegex =
new Regex("\"(?<constant>([^\"]|\\\\\")*)\"\\.Localize\\(\\)");
Applying one level of escaping to make the pattern easier to read, we get
"(?<constant>([^"]|\\")*)"\.Localize\(\)
That is, a string starts and ends with " characters, and everything between is either a non-quote or an escaped quote.
Looks like you're trying to parse code so one approach might be to evaluate the code on the fly:
var cr = new CSharpCodeProvider().CompileAssemblyFromSource(
new CompilerParameters { GenerateInMemory = true },
"class x { public static string e() { return " + input + "}}");
var result = cr.CompiledAssembly.GetType("x")
.GetMethod("e").Invoke(null, null) as string;
This way you could handle all kinds of other special cases (e.g. concatenated or verbatim strings) that would be extremely difficult to handle with regex.
new Regex(#"((([^#]|^|\n)""(?<constant>((\\.)|[^""])*)"")|(#""(?<constant>(""""|[^""])*)""))\s*\.\s*Localize\s*\(\s*\)", RegexOptions.Compiled);
takes care of both simple and #"" strings. It also takes into account escape sequences.
Related
I'm having a hard time with this one. First off, here is the difficult part of the string I'm matching against:
"a \"b\" c"
What I want to extract from this is the following:
a \"b\" c
Of course, this is just a substring from a larger string, but everything else works as expected. The problem is making the regex ignore the quotes that are escaped with a backslash.
I've looked into various ways of doing it, but nothing has gotten me the correct results. My most recent attempt looks like this:
"((\"|[^"])+?)"
In various test online, this works the way it should - but when I build my ASP.NET page, it cuts off at the first ", leaving me with just the a-letter, white space and a backslash.
The logic behind the pattern above is to capture all instances of \" or something that is not ". I was hoping this would search for \", making sure to find those first - but I got the feeling that this is overridden by the second part of the expression, which is only 1 single character. A single backslash does not match 2 characters (\"), but it will match as a non-". And from there, the next character will be a single ", and the matching is completed. (This is just my hypothesis on why my pattern is failing.)
Any pointers on this one? I have tried various combinations with "look"-methods in regex, but I didn't really get anywhere. I also get the feeling that is what I need.
ORIGINAL ANSWER
To match a string like a \"b\" c, you need to use following regex declaration:
(?:\\"|[^"])+
var rx = Regex(#"(?:\\""|[^""])+");
See RegexStorm demo
Here is an IDEONE demo:
var str = "a \\\"b\\\" c";
Console.WriteLine(str);
var rx = new Regex(#"(?:\\""|[^""])+");
Console.WriteLine(rx.Match(str).Value);
Please note the # in front of the string literal that lets us use verbatim string literals where we have to double quotes to match literal quotes and use single escape slashes instead of double. This makes regexps easier to read and maintain.
If you want to match any escaped entities in your input string, you can use:
var rx = new Regex(#"[^""\\]*(?:\\.[^""\\]*)*");
See demo on RegexStorm
UPDATE
To match the quoted strings, just add quotes around the pattern:
var rx = new Regex(#"""(?<res>[^""\\]*(?:\\.[^""\\]*)*)""");
This pattern yields much better performance than Tim Long's suggested regex, see RegexHero test resuls:
The following expression worked for me:
"(?<Result>(\\"|.)*)"
The expression matches as follows:
An opening quote (literal ")
A named capture (?<name>pattern) consisting of:
Zero or more occurences * of literal \" or (|) any single character (.)
A final closing quote (literal ")
Note that the * (zero or more) quantifier is non-greedy so the final quote is matched by the literal " and not the "any single character" . part.
I used ReSharper 9's built-in Regular Expression validator to develop the expression and verify the results:
I have used the "Explicit Capture" option to reduce cruft in the output (RegexOptions.ExplicitCapture).
One thing to note is that I am matching the whole string, but I am only capturing the substring, using a named capture. Using named captures is a really useful way to get at the results you want. In code, it might look something like this:
static string MatchQuotedString(string input)
{
const string pattern = #"""(?<Result>(\\""|.)*)""";
const RegexOptions options = RegexOptions.ExplicitCapture;
Regex regex = new Regex(pattern, options);
var matches = regex.Match(input);
var substring = matches.Groups["Result"].Value;
return substring;
}
Optimization: If you are planning on using the regex a lot, you could factor it out into a field and use the RegexOptions.Compiled option, this pre-compiles the expression and gives you faster throughput at the expense of longer initialization.
I'm trying to write a string 'clean-up' function that allows only alphanumeric characters, plus a few others, such as the underscore, period and the minus (dash) character.
Currently our function uses straight char iteration of the source string, but I'm trying to convert it to RegEx because from what I've been reading, it is much cleaner and more performant (which seems backwards to me over a straight iteration, but I can't profile it until I get a working RegEx.)
The problem is two-fold for me. One, I know the following regex...
[a-zA-Z0-9]
...matches a range of alphanumeric characters, but how do I also include the underscore, period and the minus character? Do you simply escape them with the '\' character and put them between the brackets with the rest?
Second, for any character that isn't part of the match (i.e. other punctuation like '?') we would like it replaced with an underscore.
My thinking is to instead match on a range of desired characters, we match on a single character that's not in the desired range, then replace that. I think the RegEx for that is to include the carat as the first character between the brackets like this...
[^a-zA-Z0-9]
Is that the correct approach?
Probably the most efficient way to do this is to set up a static Regex that describes the characters that you want to replace.
public static class StringCleaner
{
public static Regex invalidChars = new Regex(#"[^A-Z0-9._\-]", RegexOptions.Compiled | RegexOptions.IgnoreCase);
public static string ReplaceInvalidChars(string input)
{
return invalidChars.Replace(input, "_");
}
}
However, if you don't want the Regex to replace line ends and whitespace (like spaces and tabs) you'll need to use a slightly different expression.
public static Regex invalidChars = new Regex(#"[^A-Z0-9._\-\s]", RegexOptions.Compiled | RegexOptions.IgnoreCase);
Also, here are the rules for what you must escape to match the literal character:
Inside a set denoted by square brackets you must escape these characters -#]\ anywhere they occur and ^ only if it appears in the first position of the set to match the literal characters. Outside of a set you must escape these characters: .$^|{}[]()+?# to match the literal character.
See the following documentation for more information:
.NET Framework Regular Expressions
Regex Class
RegexOptions Enumeration
If you are trying to remove characters that you don't want, you'd be better served by Regex.Replace:
string cleaned = Regex.Replace(input, "[^a-zA-Z0-9_.]|-", "_");
To include the '-' character you can just use the Regex OR to include that character, although there probably is a way to include it in the character class, it's escaping me at the moment.
Edit: You don't actually need to explicitly include the hyphen, because it doesn't match the class anyway. That is, if you want to replace hyphen with underscore, just use [^a-zA-Z0-9_.] as your class... anything that doesn't match those classes will get replaced. But the correct way to include a hyphen in a class is to escape it with backslash (\-) or you can put it at the begging of the class list: [^-a-zA-Z0-9_.].
I think it would be perfect to use the Replace method of the string.
public string StringClean(string source, char replacement, char[] targets)
{
foreach(char c in targets)
{
//...
}
}
(Not in VS so maybe not perfect code)
If you need to replace all characters that are not on your described pattern with an underscore do this:
string result = Regex.Replace(YourOriginalString, "[^a-zA-Z0-9_.-]", "_");
I have some 100 files in which I need to replace:
Eval("something") with Eval("something").ToEncodedString()
Eval("something").ToString() with Eval("something").ToEncodedString()
I'm writing a small C# application that can automate this. But unable to form the regular expression. Would somebody help me please?
You can use this pattern: #"\bEval\(""(?<Value>.+?)""\)(?:\.ToString\(\))?"
Breakdown:
\bEval: match a word-boundary to ensure we match "Eval" as a whole word and not as part of another word
\("": literal opening parenthesis and double quotes (the double quotes appear twice since that's how they're escaped when using a verbatim string literal, i.e., the # symbol preceding the string)
(?<Value>.+?): named capture group of "Value" which is a non-greedy match of any character (will stop at double quotes)
""\): closing double quotes and closing parenthesis
(?:\.ToString\(\))?: the (?:...) bit is a non-capturing group, then we match .ToString() literally with appropriate escaping, and the final ? makes this group optional
The replacement pattern is #"Eval(""${Value}"").ToEncodedString()", which is easy to understand. The important part is that the named capture group, "Value," is referenced by using ${Value}.
Example code:
string[] inputs =
{
#"Eval(""something"")",
#"Eval(""hello"").ToString()"
};
string pattern = #"\bEval\(""(?<Value>.+?)""\)(?:\.ToString\(\))?";
string replacement = #"Eval(""${Value}"").ToEncodedString()";
foreach (var input in inputs)
{
Console.WriteLine(Regex.Replace(input, pattern, replacement));
}
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
I'm trying to write a regular expression that finds C#-style unescaped strings, such as
string x = #"hello
world";
The problem I'm having is how to write a rule that handles double quotes within the string correctly, like in this example
string x = #"before quote ""junk"" after quote";
This should be an easy one, right?
Try this one:
#".*?(""|[^"])"([^"]|$)
The first parantheses mean 'If there is an " before the finishing quote, it better be two of them', the second parantheses mean 'After the finishing quote, there sould ether be not a quote, or the end of the line'.
How 'bout the regex #\"([^\"]|\"\")*\"(?=[^\"])
Due to greedy matching, the final lookahead clause is likely not to be needed in your regex engine, although it is more specific.
If I remember correctly, you have to use \"" - the double-double quotes to hash it for C# and the backslash to hash it for regex.
Try this:
#"[^"]*?(""[^"]*?)*";
It looks for the starting characters #", for the ending characters "; (you can leave the semicolon out if you need to) and in between it can have any characters except quotes, or if there are quotes they have to be doubled.
#"(?:""|[^"])*"(?!")
is the right regex for this job. It matches the #, a quote, then either two quotes in a row or any non-quote character, repeating this up unto the next quote (that isn't doubled).
"^#(""|[^"])*$" is the regex you want, looking for first an at-sign and a double-quote, then a sequence of any characters (except double-quotes) or double double-quotes, and finally a double-quote.
As a string literal in C#, you'd have to write it string regex = "^#\"(\"\"|[^\"])*\"$"; or string regex = #"^#""(""""|[^""])*""$";. Choose your poison.