Simple regex validation - regex

Question

I want to implement the following validation. Match at least 5 digits and also some other characters between(for example letters and slashes). For example 12345, 1A/2345, B22226, 21113C are all valid combinations. But 1234, AA1234 are not. I know that {5,} gives minimum number of occurrences, but I don't know how to cope with the other characters. I mean [0-9A-Z/]{5,} won't work:(. I just don't know where to put the other characters in the regex expression.
Thanks in advance!
Best regards,
Petar

Answer 1

Using the simplest regex features since you haven't specified which engine you're using, you can try:
.*([0-9].*){5}
|/|\ /|/| |
| | \ / | | +--> exactly five occurrences of the group
| | | | +----> end group
| | | +------> zero or more of any character
| | +---------> any digit
| +------------> begin group
+--------------> zero or more of any character
This gives you any number (including zero) of characters, followed by a group consisting of a single digit and any number of characters again. That group is repeated exactly five times.
That'll match any string with five or more digits in it, along with anything else.
If you want to limit what the other characters can be, use something other than .. For example, alphas only would be:
[A-Za-z]*([0-9][A-Za-z]*){5}

Answer 2

EDIT: I'm picking up your suggestion from a comment to paxdiablo's answer: This regex now implements an upper bound of five for the number of "other" characters:
^(?=(?:[A-Z/]*\d){5})(?!(?:\d*[A-Z/]){6})[\dA-Z/]*$
will match and return a string that has at least five digits and zero or more of the "other" allowed characters A-Z or /. No other characters are allowed.
Explanation:
^ # Start of string
(?= # Assert that it's possible to match the following:
(?: # Match this group:
[A-Z/]* # zero or more non-digits, but allowed characters
\d # exactly one digit
){5} # five times
) # End of lookahead assertion.
(?! # Now assert that it's impossible to match the following:
(?: # Match this group:
\d* # zero or more digits
[A-Z/] # exactly one "other" character
){6} # six times (change this number to "upper bound + 1")
) # End of assertion.
[\dA-Z/]* # Now match the actual string, allowing only these characters.
$ # Anchor the match at the end of the string.

Answer 3

You may want to try counting the digits instead. I feel its much cleaner than writing a complex regex.
>> "ABC12345".gsub(/[^0-9]/,"").size >= 5
=> true
the above says substitute all things not numbers, and then finding the length of those remaining. You can do the same thing using your own choice of language. The most fundamental way would be to iterate the string you have, counting each character which is a digit until it reaches 5 (or not) and doing stuff accordingly.