How can I craft a regular expression to match a comma delimited list with a maximum of 5 items in the list?

Question

Examples that should match the regex:

• green, yellow-3, 12345, hello, world
• blue, red, teal, orange
• green,12345, world
• hello, there
• green

I want to create a regular expression that matches a comma-delimited list with these rules:

• The list can contain 1, 2, 3, 4, or 5 items.
• The items must not contain white space except for an optional space after each comma.
• The last item must not have a trailing comma.
• Each item must be between 2 and 30 characters.

What I have so far (doesn't work):

/^([a-z0-9]{2,30}, ?)?[a-z0-9]{2, 30}$/i

Answer 1

Try out this:

/^[a-z0-9-]{2,30}(,\s?[a-z0-9-]{2,30}){0,4}$/i

Break up:

/^
   [a-z0-9-]{2,30}   # One item for sure
   (                 # A capture group. You can make it non-capture if not required
      ,\s?              # Comma followed by optional space
      [a-z0-9-]{2,30}   # Another item
   ){0,4}            # 0 to 4 repetition.
$/ix 

You can even shorten your regex by using \w, which is equivalent to - [0-9a-zA-Z_], after your updated comment, where you said you can accept _ also. So, just use this:

/^[\w-]{2,30}(, ?[\w-]{2,30}){0,4}$/

Answer 2

Something like this should work:

/^([a-z0-9-]{2,30}, ?){0,4}[a-z0-9-]{2,30}$/i

This will match a 2 to 30 Latin letters or decimal digits or hyphens, followed by a comma and an optional space, all repeated 0 to 4 times, followed by 2 to 30 Latin letters or decimal digits or hyphens.

You can test it out here.

Answer 3

/^[^,]{2,30}(, ?[^,]{2,30}){0,4}$/

The [^,] are used because you didn't specify allowed characters so I assume that only comma is not allowed. You could of course use [a-zA-Z0-9_-], \w, or any other restrictions on that character class.