I wrote a regular expression test a certain type of string It works well but some part of me says I am not sure if there are exception that invalidates it.

type of string I need to validate are these.

'GX2480', 'H03667', 'HQ2999'

regular expression I wrote is "^[A-Z]{0,1}[A-Z0-9]{0,1}[0-9]{0,4}$"

Here is the JSBin in case anyone wants to experiment.

https://jsbin.com/yikuqonepu/edit?html,js,console

CodePudding user response：

You can test your regular expression online. The following link is one of the examples.

• https://www.regextester.com

And your regex accepts string like '', '0', 'H0' because you accept the {0} number of characters and numbers. I would change the regex into this:

"^[A-Z]{1}[A-Z0-9]{1}[0-9]{4}$"

CodePudding user response：

"^[A-Z]{0,1}[A-Z0-9]{0,1}[0-9]{0,4}$" would also match an input of only numbers or an empty input since everything is optional.

If you want to force your input to start with a letter, don't make it optional: "^[A-Z][A-Z0-9]?[0-9]{0,4}$"

Valid inputs:

• "A"
• "AB"
• "A1"
• "AB1"
• "AB1234"
• "A12345"

Invalid inputs:

• ""
• "ABC"
• "AB12345"
• "AB12C"
• "1"
• "123"

If the real question is how to match input strings of exactly length 6, the first character always being a letter, the last 4 characters always digits and the second character lettor or digit, then the regex would be:

^[A-Z][A-Z0-9][0-9]{4}$

Valid inputs:

• "AB1234"
• "A12345"

Invalid inputs:

• "A"
• "AB"
• "A1"
• "AB1"
• ""
• "ABC"
• "AB12345"
• "AB12C"
• "AB123C"
• "ABC123"
• "1"
• "123"

Alternatively, it could be formulated as follows, perhaps this is more explicit of the two different forms of inputs you allow:

^([A-Z]{2}[0-9]{4}|[A-Z][0-9]{5})$