Why does this regex with no special character match a longer string?

Question

I am using this method to try find a match, in an example:

Regex.Match(\"A2-TS-OIL\", \"TS-OIL\", RegexOptions.IgnoreCase).Success;

I got a tru

Answer 1

TS-OIL is a substring in your A2-TS-OIL. So, it would generate a match. You have the simplest match possible - literal substring. If you want TS-OIL to not match, you could also try (?!^A2-)(TS-OIL), assuming that you don't want it to start with A2-, but other things might be desired.

Answer 2

There's an implicit .* at the beginning and end of the expression string. You need to use ^ and $ which represent the start and end of the string to override that.

Answer 3

A regex match doesn't have to start at begining of the input. You might want:

^TS-OIL

if you want to only match at the start. Or:

^TS-OIL$

to prevent it matching TS-OIL-123.

^ matches the start of the input, $ matches the end.

I believe there are some place where the ^ and $ get added automatically (like web validation controls) but they're the exception.

btw, you could use:

Regex.IsMatch(...)

in this case to save a few keystrokes.

Answer 4

If you only want a match if the test string starts with your regular expression, then you need to indicate as such:

Regex.Match("A2-TS-OIL", "^TS-OIL", RegexOptions.IgnoreCase).Success;

The ^ indicates that the match must start at the beginning of the string.