RegEx match exactly 4 digits

Ok, i have a regex pattern like this /^([SW])w+([0-9]{4})$/

This pattern should match a string like SW0001 with SW-Prefix and 4 digits.

I thougth [0-9]{4} would do the job, but it also matches strings with 5 digits and so on.

Any suggestions on how to get this to work to only match strings with SW and 4 digits?

Answer

Let’s see what the regex /^([SW])w+([0-9]{4})$/ match

1. Start with S or W since character class is used
2. One or more alphanumeric character or underscore(w = [a-zA-Z0-9_])
3. Four digits

This match more than just SW0001.

Use the below regex.

/^SWd{4}$/

This regex will match string that starts with SW followed by exactly four digits.