Question

Having trouble determining if a file name conforms to a specific convention as follows. Using regular expression in C# .Net 4.0.

Valid Format: xxxxT_SSS_sss[i]_t#y.png
where

// x = Any single character.
// T = Digit: 1 to 7 inclusive.
// _SSS = Positive Integer: 000 to 999 inclusive. Always padded with leading zeros.
// _sss = Positive Integer: 000 to 999 inclusive. Always padded with leading zeros.
// i = Random text of any length including any characters. Will always be enclosed in square [] brackets. Optional.
// _t = Positive Integer: 0 to 999 inclusive. Not padded. Optional.
// #y = Positive Integer: 0 to 999 inclusive. Not padded. Optional.


UPDATE

Valid file names:

File1_000_000.png
File1_000_000_1.png
File1_000_000#2.png
File1_000_000_1#2.png
File1_000_000[text].png
File1_000_000[text]_1.png
File1_000_000[text]#2.png
File1_000_000[text]_1#2.png


The regex I’ve been trying is:

^(.{4}\\d_\\d{3}_\\d{3}(\\[\\w\\s]+\\])?(_\\d{1,3})?(\\#\\d{1,3})?)


This returns true for all the sample file names BUT, if I change File1_000_000[text]_1#2.png to File1_000_000[text]_#2.png by deleting the digit 1, it still returns true. The underscore is a part of the _t.

Answer 1

A question on regex that doesn’t involve HTML parsing, is a rarity!

Try the following:

@"^.{4}[2-7](_\d{3}){2}(\[.*?\])?(_\d{1,3})?(#\d{1,3})?\.png$"

This breaks down into:

^             Start of string
.{4}          Any character, exactly 4 times
[2-7]         A number in the range 2 - 7 once
(_\d{3}){2}   An underscore followed by 3 numbers, twice
(\[.*?\])?    An opening square bracket followed by any number of characters and closed by a square bracket 0 or 1 times
(_\d{1,3})?   An underscore followed by at least 1 and up to 3 numbers 0 or 1 times
(#\d{1,3})?   A pound (#) followed by at least 1 and up to 3 numbers 0 or 1 times
\.png$        Ending in .png