Regular Expressions and Square Brackets
Square brackets ( [ and ] ) in regular expressions can be confusing if you don't understand how they work as reserved characters. They are reserved characters twice, in two completely different ways:
1) As a set of characters to match, as in [A-Za-z] matches all upper and lower case characters a-z
2) Used for negation, as in [^x] matches NOT x. The carrot, ^, in square brackets, means "not".
This is what makes questions like this tricky:
Since square brackets are reserved for these purposes, you'll need to escape them. Note that this can vary from regexp engine to regexp engine. In C# try this.
Let's translate the regular expression \[(?<myMatch>([^\]])*)\]
First, the Groups syntax. In C# regular expressions, you can give your matches a name. This is a .NET regex thing, so don't expect it if you're using other regex engines. You "name" your regexps like this:
(?<variableName>(REGEX GOES HERE))
You don't have to do it this way, and you can just group your regular expressions with ( ) and index into them. Your pick.
- We start matching at a square bracket. Because square brackets are reserved characters (see #1 and #2 above), we'll escape it with back slash to say "No really, I mean a square bracket, not a reserved character. Look, I'm escaping it to say I mean it!" This is the beginning "\[".
- Next, we use the (?<myMatch> syntax as a convenience.
- Now we get to the heart of it: ([^\]])*). This says: keep going until you hit a closing square bracket. This is use of square brackets #2 above: negation. The * means "any number of those". For example, if you have the regexp [^a]* and the string "bobcat" you'd get "bobc". Make sense? I think of it as "everything up to, but not including".
- Finally, end the madness with a square bracket. Again: no, really, I'm escapging it with a "\" to say I REALLY DO mean the character "]"
1) As a set of characters to match, as in [A-Za-z] matches all upper and lower case characters a-z
2) Used for negation, as in [^x] matches NOT x. The carrot, ^, in square brackets, means "not".
This is what makes questions like this tricky:
Here's the answer:Hi guys,
Hoping someone can help me out with this
I have a string "Setup.exe [sometext] [someOtherText]"
I need to be able to extract the the text between the [ and ]
Would anyone be able to help me out with this?
Also I'm never going to know how many " [ ] " Im going to have
Thanks in advance
Since square brackets are reserved for these purposes, you'll need to escape them. Note that this can vary from regexp engine to regexp engine. In C# try this.
using System;
using System.Text.RegularExpressions;
class Test{
public static void Main(){
string s = "Setup.exe [sometext] [someothertext] [and more text here]";
string pattern = @"\[(?<myMatch>([^\]])*)\]";
Regex r = new Regex(pattern);
MatchCollection m = r.Matches(s);
foreach(Match match in m){
Console.WriteLine(match.Groups["myMatch"]);
}
}
}
Let's translate the regular expression \[(?<myMatch>([^\]])*)\]
First, the Groups syntax. In C# regular expressions, you can give your matches a name. This is a .NET regex thing, so don't expect it if you're using other regex engines. You "name" your regexps like this:
(?<variableName>(REGEX GOES HERE))
You don't have to do it this way, and you can just group your regular expressions with ( ) and index into them. Your pick.
- We start matching at a square bracket. Because square brackets are reserved characters (see #1 and #2 above), we'll escape it with back slash to say "No really, I mean a square bracket, not a reserved character. Look, I'm escaping it to say I mean it!" This is the beginning "\[".
- Next, we use the (?<myMatch> syntax as a convenience.
- Now we get to the heart of it: ([^\]])*). This says: keep going until you hit a closing square bracket. This is use of square brackets #2 above: negation. The * means "any number of those". For example, if you have the regexp [^a]* and the string "bobcat" you'd get "bobc". Make sense? I think of it as "everything up to, but not including".
- Finally, end the madness with a square bracket. Again: no, really, I'm escapging it with a "\" to say I REALLY DO mean the character "]"
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