Regular expression for specific file mask - regex

Question

I want to have 2 regex patterns that checks files after specific file mask. The way I like to do it is written below.
Pattern 1:
check if the left side of _ has 7 digits.
checks if the right side of _ is numeric.
checks for the specified extension is there.
the input will look like this : 1234567_1.jpg
Pattern 2:
check if there is 10 digits to the left of a "Space" char
check if there is 4 digits to the right of a "Space" char
check to the right side of _ is numeric
check for the specified extension is there.
The input will look like this: 1234567891 1234_1.png
As stated above this is to be used to check for a specific file mask.
i have been playing around with ideas like : ^[0-9][0-9].jpg$
and ^[0-9] [0-9][0-9].jpg$ is my first tries.
i do apologies for not providing my tries.

Answer 1

I suggest combining patterns with | (or):
string pattern = string.Join("|",
#"(^[0-9]{7}_[0-9]+\.jpg$)", // 1st possibility
#"(^[0-9]{10} [0-9]{4}_[0-9]+\.png$)"); // 2nd one
....
string fileName = #"c:\myFiles\1234567_1.jpg";
// RegexOptions.IgnoreCase - let's accept ".JPG" or ".Jpg" files
if (Regex.IsMatch(Path.GetFileName(fileName), pattern, RegexOptions.IgnoreCase)) {
...
}
Let's explain the second pattern: (^[0-9]{10} [0-9]{4}_[0-9]+\.jpg$)
^ - anchor (string start)
[0-9]{10} - 10 digits - 0-9
- single space
[0-9]{4} - 4 digits
_ - single underscope
[0-9]+ - one or more digits
\.png - .png (. is escaped)
$ - anchor (string end)

Answer 2

This should work for first regex:
\d{7}_\d*.(jpg|png)
This should work for second regex:
\d{10}\s\d{4}_\d*.(jpg|png)
If you want to use them together just do it like below:
(\d{7}_\d*.(jpg|png)|\d{10}\s\d{4}_\d*.(jpg|png))
In this group (jpg|png) you can just add another extensions by separating them with | (or).
You can check if it works for you at: https://regex101.com/
Cheers!