Add string after a specified string

Question

Say I have the following HTML string

<head>

</head>

<body>
<img src="stickman.gif" width="24" height="39" alt="Stickman">
<a href="http://www.w3schools.com">W3Schools</a>
</body>

I want to add a string in between the <head> tags. So the final HTML string become

<head>
<base href="http://www.w3schools.com/images/">
</head>

<body>
<img src="stickman.gif" width="24" height="39" alt="Stickman">
<a href="http://www.w3schools.com">W3Schools</a>
</body>

So I have to search for the first occurrence of the <head> string then insert <base href="http://www.w3schools.com/images/"> right after.

How do I do this in C#.

You can do this in more ways then one: -Regular Expressions -Splitting your text by a certain character and writing the data you have gotten with the line you need to add -Using an XMLreader/writer — Ken de Jong
– Ken de Jong, Commented May 13, 2013 at 8:10
Regex is really overkill for what you want to do here. Simple .NET string manipulation is good enough and a lot less complex. — pyrocumulus
– pyrocumulus, Commented May 13, 2013 at 8:18
Don't use RegEx when manipulating HTML/XML, because HTML is not regular, and RegEx is for manipulating Regular Expressions. — abelenky
– abelenky, Commented May 13, 2013 at 8:25
@abelenky: Since when is RegEx for manipulating Regular Expressions? — Mesh
– Mesh, Commented May 13, 2013 at 8:39

dav_i · Accepted Answer · 2013-05-13 08:14:49Z

7

So why not just do something easy like

myHtmlString.Replace("<head>", "<head><base href=\"http://www.w3schools.com/images/\">");

Not the most elegant or expandable, but satisfies the conditions of your question.

answered May 13, 2013 at 8:14

dav_i

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4 Comments

PutraKg Over a year ago

For some reason it does not found the `<head>' tag if there's some other string before it

dav_i Over a year ago

The above doesn't care if there is something before or after it. There must be something else going on if it's not working.

Jodrell Over a year ago

@PutraKg, your question doesn't have any text before the head tag. Is this question about all html? stackoverflow.com/a/1732454/659190

PutraKg Over a year ago

The question showed is just one example. I am testing the answer against real websites too. Sorry for not mentioning that as I forgot to consider against doctype etc when writing the question.

gzaxx · Accepted Answer · 2013-05-13 08:15:45Z

5

Another way of doing this:

string html = "<head></head><body><img src=\"stickman.gif\" width=\"24\" height=\"39\" alt=\"Stickman\"><a href=\"http://www.w3schools.com\">W3Schools</a></body>";
var index = html.IndexOf("<head>");

if (index >= 0)
{
     html = html.Insert(index + "<head>".Length, "<base href=\"http://www.w3schools.com/images/\">");
}

answered May 13, 2013 at 8:15

gzaxx

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Comments

Draykos · Accepted Answer · 2013-05-13 08:22:05Z

2

This is how can it be done with Regex, if you prefer to use it

public string ReplaceHead(string html)
{
    string rx = "<head[^>]*>((.|\n)*?)head>";
    Regex r = new Regex(rx);
    MatchCollection matches = r.Matches(html);
    string s1, s2;
    Match m = matches[0];
    s1 = m.Value;
    s2 = "<base href="http://www.w3schools.com/images/">" + s1;
    html = html.Replace(s1, s2);
    return html;
}

answered May 13, 2013 at 8:22

Draykos

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4 Comments

Draykos Over a year ago

no, it's not. Question was not: "which is the easier way to do it", but "how can it be done with regex" (but now it has been edited) Anyway can be useful to check what you have inside the tag before doing the replace, that's why I uses a similar solution in a project of mine

PutraKg Over a year ago

I would use this but some people suggested that in my situation regex would probably be over-killed. So I edited my question and remove the regex preference. Anyway, I appreciate your answer.

Draykos Over a year ago

It's overkill if you are sure to have only 1 <head> tag, and you are sure the string you'll add it's not already inside the tag. With my solution you can check if "w3schools.com/images" etc is already inside before doing replace. Of course this is silly in the example, but it can be different for a real case

Draykos Over a year ago

As one of the answer of the thread Jodrell has linked: "I like to parse HTML with regular expressions. I don't attempt to parse idiot HTML that is deliberately broken."

Mesh · Accepted Answer · 2013-05-13 10:53:09Z

1

Just replace the HEAD's tail, in HTML there should only be one:

"<head></head>".Replace( "</head>" , "<a href=\"http://www.w3fools.com\">W3Fools</a>" + "</head>" );

You can flip this around to and replace the HEAD's open, to insert a tag at the beginning.

If you need anything more complex then you should look into using parsed HTML.

edited May 13, 2013 at 10:53

answered May 13, 2013 at 8:15

Mesh

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1 Comment

Jodrell Over a year ago

What do you mean by proper html? I agree with the last part.

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