Help needed for Regular expression.

Question

I have a string like:

[a b="c" d="e"]Some multi line text[/a]

Now the part d="e" is optional. I want to convert such type of string into:

<a b="c" d="e">Some multi line text</a>

The values of a b and d are constant, so I don't need to catch them. I just need the values of c, e and the text between the tags and create an equivalent xml based expression. So how to do that, because there is some optional part also.

Answer 1

If you are actually thinking of processing (pseudo)-HTML using regexes,

don't

SO is filled with posts where regexes are proposed for HTML/XML and answers pointing out why this is a bad idea.

Suppose your multiline text ("which can be anything") contains

[a b="foo" [a b="bar"]]

a regex cannot detect this.

See the classic answer in: http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags

which has:

I think it's time for me to quit the post of Assistant Don't Parse HTML With Regex Officer. No matter how many times we say it, they won't stop coming every day... every hour even. It is a lost cause, which someone else can fight for a bit. So go on, parse HTML with regex, if you must. It's only broken code, not life and death. – bobince

Seriously. Find an XML or HTML DOM and populate it with your data. Then serialize it. That will take care of all the problems you don't even know you have got.

Answer 2

Would some multiline text include [ and ]? If not, you can just replace [ with < and ] with > using string.replace - no need of regex.

Update: If it can be anything but [/a], you can replace

^\[a([^\]]+)](.*?)\[/a]$

with

<a$1>$2</a>

I haven't escaped ] and / in the regex - escape them if necessary to get

^\[a([^\]]+)\](.*?)\[\/a\]$

Answer 3

Hi

For HTML tags, please use HTML parser.

For [a][/a], you can do like following

Match m=Regex.Match(@"[a b=""c"" d=""e""]Some multi line text[/a]", 
                    @"\[a b=""([^""]+)"" d=""([^""]+)""\](.*?)\[/a\]",
                    RegexOptions.Multiline);

m.Groups[1].Value
"c"
m.Groups[2].Value
"e"
m.Groups[3].Value
"Some multi line text"

Here is Regex.Replace (I am not that prefer though)

string inputStr = @"[a b=""[[[[c]]]]"" d=""e[]""]Some multi line text[/a]";
string resultStr=Regex.Replace(inputStr,
                            @"\[a( b=""[^""]+"")( d=""[^""]+"")?\](.*?)\[/a\]",
                            @"<a$1$2>$3</a>", 
                            RegexOptions.Multiline);