Hi, I am trying to come up with PHP regular expression for our local vehicle registration plate numbers, our number plate is like B123ABC

Let’s look at your example:

/B+[101-999].{3,3}+[a-zA-Z].{3,3}/i

B+ here should just be B, because you always want just exactly one. B+ means "one or more of B."

[101-999] doesn’t do what you think, it does not provide an integer range. You can only supply single character ranges. Which means you’ll want to handle each digit individually, so the first digit could be 1-9, the second could be 0-9, and the third could be 1-9:

[1-9][0-9][1-9]

Then you want exactly three letters from A to Z. One letter from A to Z is [A-Z], and then to make that happen exactly three times, you’d follow it with {3, 3} but note there’s a shortcut. If both numbers are the same, you only have to provide it once like {3}. So this part becomes [A-Z]{3}.

Overall, you’ll have:

/B[1-9][0-9][1-9][A-Z]{3}/

Then, if you want lowercase to work as well, add your i at the end:

/B[1-9][0-9][1-9][A-Z]{3}/i

This will match all plate numbers in a string, even if there are more than one. If you want to test a string to see if it contains only a single valid plate number, then you can use the start ^ and end $ anchors to mark the start and end of the string:

/^B[1-9][0-9][1-9][A-Z]{3}$/

So this means:

• the start of the string
• exactly one B
• one digit from 1 to 9
• one digit from 0 to 9
• one digit from 1 to 9
• one letter from A to Z, three times
• the end of the string
• and I don’t care about letter casing

Note if you have [A-Za-z] then you don’t also need /i at the end, they do they same thing.