Question

I would like to validate a user’s input of indexing tags for posts by running them through a regular expression in Codeigniter’s validation library.

Ideally, the regex would have the following conditions:

1. allow only letters and numbers
2. tags will be considered unique entities if separated by space (any number) or comma (any number)
3. there should be a limit to the number of tags (for ex in this case 6)

There are a few partial solutions to this here on SO:

• For alphanumeric tags separated by commas?
• Regex for comma separated text

but they do not fully resolve my issue.

Any suggestions?

Answer 1

If all you want is validating, then this should do:

^[a-zA-Z0-9]+(?:[ ,]+[a-zA-Z0-9]+){0,5}$

Same regex, but with comments and whitespace:

^ #beginning of string
[a-zA-Z0-9]+ #any sequence of alphanumeric letters
(?: #start of non capturing group
    [\ ,]+ #between 1 and int delimiting chars
    [a-zA-Z0-9]+ #again, any sequence of alphanumeric letters
) #end of non capturing group
{0,5} #allow between 0 and n-1 occurrences of preceding group
$ #end of string

To allow input with leading/trailing spaces/commas, change regex to this:

^[ ,]*[a-zA-Z0-9]+(?:[ ,]+[a-zA-Z0-9]+){0,5}[ ,]*$

and to further allow input with zero tags, change regex to this:

^[ ,]*(?:[a-zA-Z0-9]+(?:[ ,]+[a-zA-Z0-9]+){0,5})?[ ,]*$