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

[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).

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.

The a-z matchs 'a' to 'z' A-Z matchs 'A' to 'Z' A-z matches all these as well as the characters between the 'Z' and 'a' which are [ ] ^ / _ `

Refer to http://www.asciitable.com/

Take a look at ASCII table. You'll see that there are some characters between Z and a, so you will match more than you intented to.

The square brackets create a character class and the hyphen is a shorthand for adding every character between the two provided characters. i.e. [A-F] can be written [ABCDEF].

The character class [A-z] will match every character between those characters, which in ASCII includes some other characters such as '[', '\' and ']'.

An alternative to specifying both cases would be to set the regular expression to be case-insensitive, by using the /i modifier.