dotnet中正则表达式之间的区别

Question

what is the difference between the two regex

new Regex(@"(([[[{""]))", RegexOptions.Compiled)

and

new Regex(@"(^[[[{""])", RegexOptions.Compiled) 

I've used the both regex but can't find the difference. it's almost match similar things.

Answer 1

The regex patterns are not well written because

1. There are duplicate characters in character classes (thus redundant)
2. The first regex contains duplicate capture group on the whole pattern.

The first regex - (([[[{""])) - matches 1 character, either a [ , a { , or a " , and captures it into Group 1 and Group 2. See demo . It is equal to

[[{"]

Demo

The second regex - (^[[[{""]) - only matches the same characters as the pattern above, but at the beginning of a string (if RegexOptions.Multiline is not set), or the beginning of a line (if that option is set). See demo . It is equal to

^[[{"]

See demo

You will access the matched characters using Regex.Match(s).Value .

More about anchors

Aslo see Caret ^: Beginning of String (or Line)