Need a regex that validates a string with varying size

I need regex that validates a string that:

• has 4 or 5 letters
• then o开发者_StackOverflow社区ne underscore
• then either an I or O (only one of them)
• then one underscore
• then 4 numeric digits

Now here where it complicates further. After all that it may have:

• another underscore
• then 4 numeric digits.

In the end all these must be valid:

ASDF_I_0002

ASDFG_O_0003_0324

ASDF_O_0001

ASDF_I_0001_0001

Thank you.

• has 4 or 5 letters (A-Z)

  [A-Z]{4,5}
  

• then one underscore

  [A-Z]{4,5}_
  

• then either an I or O (only one of them)

  [A-Z]{4,5}_[IO]
  

• then one underscore

  [A-Z]{4,5}_[IO]_
  

• then 4 numeric digits

  [A-Z]{4,5}_[IO]_[0-9]{4}
  

After all that it may have:

    [A-Z]{4,5}_[IO]_[0-9]{4}()?

• another underscore

  [A-Z]{4,5}_[IO]_[0-9]{4}(_)?
  

• then 4 numeric digits.

  [A-Z]{4,5}_[IO]_[0-9]{4}(_[0-9]{4})?
  

You've lined out your requirements so nicely, I wonder where the problem was to make a regex from them. ;)

Try this one

^\w{4,5}_(I|O)_\d{4}(_\d{4})?$

EDIT: Compared to other solutions it evaluates ;-)

^\w{4,5}_[IO](_\d{4}){1,2}$

has 4 or 5 letters

• \w{4-5}

then one underscore

• _

then either an I or O (only one of them)

• [IO]

then one underscore

• _

then 4 numeric digits

• \d{4}

Put it all together

\w{4-5}_[IO]_\d{4}

Although to match all your test cases you need to extend this

\w{4-5}_[IO](_\d{4}){1,2}