regex validation

Question

I am trying to validate a string of 3 numbers followed by / then 5 more numbers I thought this would work

(/^([0-9]+[0-9]+[0-9]+/[0-9]+[0-9]+[0-9]+[0-9]+[0-9])/i)

but it doesn't, any ideas what i'm doing wrong

Answer 1

Try this

preg_match('@^\d{3}/\d{5}@', $string)

The reason yours is not working is due to the + symbols which match "one or more" of the nominated character or character class.

Also, when using forward-slash delimiters (the characters at the start and end of your expression), you need to escape any forward-slashes in the pattern by prefixing them with a backslash, eg

/foo\/bar/

PHP allows you to use alternate delimiters (as in my answer) which is handy if your expression contains many forward-slashes.

Answer 2

First of all, you're using / as the regexp delimiter, so you can't use it in the pattern without escaping it with a backslash. Otherwise, PHP will think that you're pattern ends at the / in the middle (you can see that even StackOverflow's syntax highlighting thinks so).

Second, the + is "greedy", and will match as many characters as it can, so the first [0-9]+ would match the first 3 numbers in one go, leaving nothing for the next two to match.

Third, there's no need to use i, since you're dealing with numbers which aren't upper- or lowercase, so case-sensitivity is a moot point.

Try this instead

/^\d{3}\/\d{5}$/

The \d is shorthand for writing [0-9], and the {3} and {5} means repeat 3 or 5 times, respectively.

(This pattern is anchored to the start and the end of the string. Your pattern was only anchored to the beginning, and if that was on purpose, the remove the $ from my pattern)

Answer 3

I recently found this site useful for debugging regexes: http://www.regextester.com/index2.html

It assumes use of /.../ (meaning you should not include those slashes in the regex you paste in).

So, after I put your regex ^([0-9]+[0-9]+[0-9]+/[0-9]+[0-9]+[0-9]+[0-9]+[0-9]) in the Regex box and 123/45678 in the Test box I see no match. When I put a backslash in front of the forward slash in the middle, then it recognizes the match. You can then try matching 1234/567890 and discover it still matches. Then you go through and remove all the plus signs and then it correctly stops matching.

What I particularly like about this particular site is the way it shows the partial matches in red, allowing you to see where your regex is working up to.