Regex validation of filename failing

Question

I'm trying to validate a filename having letters "CAT" or "DOG" followed by 8 numerics, and ending in ".TXT".

Examples:

CAT20000101.TXT
DOG20031212.TXT

This would NOT match:

ATA12330000.TXT
CAT200T0101.TXT
DOG20031212.TX1

Here's the regex I am trying to make work:

(([A-Z]{3})([0-9]{8})([\.TXT]))\w+

Why is the last section (.TXT) failing against non-matching file extensions?

See example: http://regexr.com/3a7fo

Answer 1

Inside character class there is no regex grouping hence [\\.TXT] is not right.

You can use this regex:

^[A-Z]{3}[0-9]{8}\.TXT$

For only matching CAT and DOG use:

^(CAT|DOG)[0-9]{8}\.TXT$

Answer 2

1. lose the unnecessary parentheses

[AZ]{3}[0-9]{8}[\\.TXT]\\w+

2. lose the unnecessary/pattern-breaking character class [] around \\.TXT

[AZ]{3}[0-9]{8}\\.TXT\\w+

3. lose the \\w+ at the end

[AZ]{3}[0-9]{8}\\.TXT

4. change [AZ]{3} to (?:CAT|DOG) .

(?:CAT|DOG)[0-9]{8}\\.TXT

voilà.

Answer 3

It's failing because \\.TXT is in square brackets, which matches only one of those four characters. Just use (\\.TXT) .

Answer 4

删除[.TXT]到.TXT周围的方括号您的示例已修改http://regexr.com/3a7fu