Regular expression "^[a-zA-Z]" or "[^a-zA-Z]"
Is there a difference between ^[a-zA-Z]
and [^a-zA-Z]
?
When I check in C#,
Regex.IsMatch("t", "^[a-zA-Z]") // Returns true (I think it's correct)
Regex.IsMatch("t", "[^a-zA-Z]") // Returns false
There are a lot of web sites using [^a-zA-Z]
for the alphabet. I'm not really sure which one is 开发者_如何学Gocorrect answer.
Yes, the first means "match all strings that start with a letter", the second means "match all strings that contain a non-letter". The caret ("^") is used in two different ways, one to signal the start of the text, one to negate a character match inside square brackets.
^[a-zA-Z]
means any a-z or A-Z at the start of a line
[^a-zA-Z]
means any character that IS NOT a-z OR A-Z
There is a difference.
When the ^
character appears outside of []
matches the beginning of the line (or string). When the ^
character appears inside the []
, it matches any character not appearing inside the []
.
^ outside of the character class ("[a-zA-Z]") notes that it is the "begins with" operator.
^ inside of the character negates the specified class.
So, "^[a-zA-Z]" translates to "begins with character from a-z or A-Z", and "[^a-zA-Z]" translates to "is not either a-z or A-Z"
Here's a quick reference: http://www.regular-expressions.info/reference.html
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