Regular Expression to match last word when string starts with pattern - regex

Question

I'm trying to create a regex to match the last word of a string, but only if the string starts with a certain pattern.
For example, I want to get the last word of a string only if the string starts with "The cat".
"The cat eats butter" -> would match "butter".
"The cat drinks milk"-> would match "milk"
"The dog eats beef" -> would find no match.
I know the following will give me the last word:
\s+\S*$
I also know that I can use a positive look behind to make sure a string starts with a certain pattern:
(?<=The cat )
But I can't figure out to combine them.
I'll be using this in c# and I know I could combine this with some string comparison operators but I'd like this all to be in one regex expression, as this is one of several regex pattern string that I'll be looping through.
Any ideas?

Answer 1

Use the following regex:
^The cat.*?\s+(\S+)$
Details:
^ - Start of the string.
The cat - The "starting" pattern.
.*? - A sequence of arbitrary chars, reluctant version.
\s+ - A sequence of "white" chars.
(\S+) - A capturing group - sequence of "non-white" chars,
this is what you want to capture.
$ - End of the string.
So the last word will be in the first capturing group.

Answer 2

What about this one?
^The\scat.*\s(\w+)$

Answer 3

My regex knowdlege is quite rusty, but couldn't you simply "add" the word you are looking for at the start of \s+\S*$, if you know that will return the last word?
Something like this then (the "\" is supposed to be the escape sign so it's read as the actual word):
\T\h\e\ \c\a\t\ \s+\S*$

Answer 4

Without Regex
No need for regex. Just use C#'s StartsWith with Linq's Split(' ').Last().
See code in use here
using System;
using System.Linq;
using System.Text.RegularExpressions;
class Example {
static void Main() {
string[] strings = {
"The cat eats butter",
"The cat drinks milk",
"The dog eats beef"
};
foreach(string s in strings) {
if(s.StartsWith("The cat")) {
Console.WriteLine(s.Split(' ').Last());
}
}
}
}
Result:
butter
milk
With Regex
If you prefer, however, a regex solution, you may use the following.
See code in use here
using System;
using System.Text.RegularExpressions;
class Example {
static void Main() {
string[] strings = {
"The cat eats butter",
"The cat drinks milk",
"The dog eats beef"
};
Regex regex = new Regex(#"(?<=^The cat.*)\b\w+$");
foreach(string s in strings) {
Match m = regex.Match(s);
if(m.Success) {
Console.WriteLine(m.Value);
}
}
}
}
Result:
butter
milk