Difference between regex [A-z] and [a-zA-Z]

Question

I am using a regex to program an input validator for a text box where I only want alphabetical characters. I was wondering if [A-z] and [a-zA-Z] were equivalent or if there were differences performance wise.

I keep reading [a-zA-Z] on my searches and no mention of [A-z].

I am using java's String.matches(regex).

Answer 1

[A-z] will match ASCII characters in the range from A to z, while [a-zA-Z] will match ASCII characters in the range from A to Z and in the range from a to z. At first glance, this might seem equivalent -- however, if you look at this table of ASCII characters, you'll see that A-z includes several other characters. Specifically, they are [, \, ], ^, _, and ` (which you clearly don't want).

Answer 2

When you take a look at the ASCII table, you will see following:

A = 65 Z = 90 a = 97 z = 122 

So, [A-z] will match every char from 65 to 122. This includes these characters (91 -> 96) as well:

[\]^_` 

This means [A-Za-z] will match only the alphabet, without the extra characters above.