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

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北海茫月
北海茫月 2020-11-22 08:39

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] we

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  • 2020-11-22 09:16

    [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).

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  • 2020-11-22 09:20

    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.

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  • 2020-11-22 09:23

    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.

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  • 2020-11-22 09:23

    Take a look at the ASCII chart (which Java characters are based on): there are quite a few punctuation characters situated between Z and a, namely these:

    [\]^ _`
    
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  • 2020-11-22 09:31

    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.

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  • 2020-11-22 09:34

    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/

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