regex to extract number from a chain type "height/width/lenght: 12.5/15.4/14"

What programming language or text editor are you using? In its most simplistic form, this may suffice:

(\d+(\.\d+)?)/(\d+(\.\d+)?)/(\d+(\.\d+)?)

Select allOpen in new window

Inspect capture groups 1, 3, & 5.

Depending on what regex engine you have available to you, you can get more elaborate:

(\d+(?:\.\d+)?)/(\d+(?:\.\d+)?)/(\d+(?:\.\d+)?)

Select allOpen in new window

Inspect capture groups 1, 2, & 3.

(?<height>\d+(?:\.\d+)?)/(?<width>\d+(?:\.\d+)?)/(?<length>\d+(?:\.\d+)?)

Select allOpen in new window

Inspect capture groups "height", "width" and "length".

I'm glad you answered as far I can see, you are the "best".

I'm using c# and inspecting a RichTextBox on a Windows Forms app.
I already understand that I was not clear enough. Sorry! I will try explain better.

height, width and lenght were just examples.

Imagine
                 xxx/aaa/bbb: 12.4/25/23.5
                 aaa/bbb/xxx: 25/23.5/12.4
                 aaa/bbb/xxx/yyy: 25/23.5/12.4/30

I'm looping for each string so, if i'm working with xxx I need to have always 12.5 . What I want is the number in same relative position. Hope it is clear now!
thks kaufmed foy your availability

If you can have an arbitrary number of items, then I don't think regex is a good choice. A couple of Splits should suffice.

e.g.

static string GetValueByKey(string key, string keyValues)
{
    string[] keysAndValues = keyValues.Split(':');
    string keys = keysAndValues[0];
    string values = keysAndValues[1];
    int targetIndex = -1;

    foreach (string availableKey in keys.Split('/'))
    {
        targetIndex++;

        if (string.Equals(key, availableKey.Trim(), StringComparison.OrdinalIgnoreCase))
        {
            break;
        }
    }

    if (targetIndex < 0)
    {
        throw new ApplicationException("Key not found!");
    }

    string[] availableKeys = values.Split('/');

    if (targetIndex >= availableKeys.Length)
    {
        throw new ApplicationException("Not enough values supplied!");
    }

    return availableKeys[targetIndex].Trim();
}

Select allOpen in new window

Usage

string keyValues = "xxx/aaa/bbb: 12.4/25/23.5";
//string keyValues = "aaa/bbb/xxx: 25/23.5/12.4";
//string keyValues = "aaa/bbb/xxx/yyy: 25/23.5/12.4/30";
string value = GetValueByKey("xxx", keyValues);

Select allOpen in new window

There's minimal error handling in the above function. You'll need to add in whatever you think you might encounter in production.

that's perfect for my example!
I was looking for regex once there are guys that are using " " instead  the ":" And this is just an example!
I talk about emails from hundreds/thousands guys about a specific theme, so the main keywords are known! Terrible to get the good numbers, sometimes! As an example, if I have someone writing "width" instead "width", or "tmw" instead "twm", how can I guess?
Thks very much for your help, but I see (magical) regex cannot help me always!