Replace a specified string within a string which matches the regex pattern c#

Question

I have a multiline text box which contains below string URLs:

http://foodfacts.ambigouos.com
http://articles.ambigouos.com
http://www.dirtshirt.org

I want to replace/update a string http to https from the above URLs which has ambigouos.com as a domain with Regex.

Expected output:

https://foodfacts.ambigouos.com
https://articles.ambigouos.com
http://www.dirtshirt.org

Below code tried but not working:

multilinebox.text = Regex.Replace(multilinebox.text, @"^http?://[a-zA-Z]*(\.ambigouos\.com)$", "$1", RegexOptions.IgnoreCase);

Thanks in advance.

Below code tried but not working How specifically is it not working? — mjwills
– mjwills, Commented Mar 6, 2018 at 11:21
You're aware that your regex matches http:// or htt://, right? — ProgrammingLlama
– ProgrammingLlama, Commented Mar 6, 2018 at 11:23
you might not need regexp, just check if line .Contains("ambigouos.com") and then do .Replace("http://", "https://") — trailmax
– trailmax, Commented Mar 6, 2018 at 11:25
@trailmax That is true if only OP does not want to make sure only an HTTP link is changed. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Mar 6, 2018 at 11:26

Wiktor Stribiżew · Accepted Answer · 2018-03-08 12:03:16Z

2

You may leverage the fact that the strings are at the start of a line (i.e. you should compile the regex with the RegexOptions.Multiline flag), you do not need to check the end of the string/line here. Also, you need to set the grouping construct around the whole non-fixed part of the string.

If you need to only handle matches at the start of a line use

Regex.Replace(multilinebox.text, @"^http://((?:[^/]*\.)?ambigouos\.com)", "https://$1", 
     RegexOptions.IgnoreCase | RegexOptions.Multiline);

If you want to handle matches anywhere inside a string remove ^ and | RegexOptions.Multiline use

Regex.Replace(multilinebox.text, 
          @"http://((?:[^/]*\.)?ambigouos\.com)", 
          "https://$1", 
          RegexOptions.IgnoreCase);

See the regex demo.

Detasils

^ - start of a line (since RegexOptions.Multiline is used)
http:// - a literal substring
((?:[^/]*\.)?ambigouos\.com) - Capturing group 1:
- (?:[^/]*\.)? - an optional sequence of any 0+ chars other than /, and then a .
- ambigouos\.com - a literal substring.

You may add \r\n to the negated character class to avoid overflowing across lines, i.e. [^/] => [^/\r\n].

edited Mar 8, 2018 at 12:03

answered Mar 6, 2018 at 11:23

Wiktor Stribiżew

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7 Comments

user7030548 Over a year ago

http://foodfacts.ambigouos.com/ is not matching with the above regex hence not replacing to https://foodfacts.ambigouos.com/ suggest!!

Wiktor Stribiżew Over a year ago

@PPB It does, look here. Here is a C# demo.

Wiktor Stribiżew Over a year ago

@PPB Do you mean to say you do not need to match these URLs at the start of a line but anywhere inside the string?

Wiktor Stribiżew Over a year ago

@PPB But that means you want to match http:// at the start of a line. There is no need removing ^ start-of-line anchor. Have you added the RegexOptions.Multiline option? Show the exact code you have at IDEONE.

user7030548 Over a year ago

Let us continue this discussion in chat.

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