Question

I need to write a regular expression to verify if a file input follows a rule:

A111B2_3_C.exe

in which:

• A: compulsory, it must be a’A’
• 111: compulsory, it is a natural number
• B: compulsory, it must be a’B’
• 2: compulsory, it is in range from 1->6
• _: compulsory, it must be ‘_’
• 3: compulsory, it must be a nature number
• _: optional if C followed, it must be ‘_’
• C: optional, C is a natural number
• .exe: is the end extension of the file

It should be accepted this one: A111B2_3_.exe as well. but A111B2_3_0.exe is not accepted. the number after 3_ must be greater than 0.

Thanks in advance.

Answer 1

It’s a bit hard to understand your requirements, but here’s a regex that should do what you want:

A\d+B[1-6]_\d+(_\d+)?\.exe

Explanation:

1. A — The letter ‘A’
2. \d+ — 1 or more numbers
3. B — The letter ‘B’
4. [1-6] — A single number: 1, 2, 3, 4, 5, or 6
5. _ — An underscore
6. \d+ — 1 or more numbers
7. (_\d+)? — Optionally, an underscore followed by 1 or more numbers
8. \. — A period
9. exe — The letters ‘exe’

Edit: In response to your comments, here is a regex that will also accept A111B2_3_.exe:

A\d+B[1-6]_\d+(_\d*)?\.exe

I changed the last \d+ (one or more numbers) to \d* (zero or more numbers).

Edit 2: Now I’ve changed \d* to ([1-9]\d*)?. What that means is left as an exercise to the reader.

A\d+B[1-6]_\d+(_([1-9]\d*)?)?\.exe