CODEWITHSUNDEEP
regex
Laoujin
Laoujin

Reputation: 10239

Match specific length x or y

I'd like a regex that is either X or Y characters long. For example, match a string that is either 8 or 11 characters long. I have currently implemented this like so: ^([0-9]{8}|[0-9]{11})$.

I could also implement it as: ^[0-9]{8}([0-9]{3})?$

My question is: Can I have this regex without duplicating the [0-9] part (which is more complex than this simple \d example)?

Upvotes: 49

Views: 41216

Answers (3)

Tim Pietzcker
Tim Pietzcker

Reputation: 336418

There is one way:

^(?=[0-9]*$)(?:.{8}|.{11})$

or alternatively, if you want to do the length check first,

^(?=(?:.{8}|.{11})$)[0-9]*$

That way, you have the complicated part only once and a generic . for the length check.

Explanation:

^        # Start of string
(?=      # Positive lookahead, assert that the following regex can be matched here:
  [0-9]* # any number of digits (and nothing but digits)
  $      # until end of string
)        # (End of lookahead)
(?:      # Non-capturing group, match either
  .{8}   # 8 characters
  |      # or
  .{11}  # 11 characters
)        # (End of alternation)
$        # End of string

Upvotes: 77

Toto
Toto

Reputation: 91508

With Perl, you could do:

my $re = qr/here_is_your_regex_part/;
my $full_regex = qr/$re{8}(?:$re{3})?$/

Upvotes: 2

Declan McKenna
Declan McKenna

Reputation: 4910

For those of us looking to capture different lengths of the same multiple try this.

^(?:[0-9]{32})+$

Where 32 is the multiple you want to capture all lengths for (32, 64, 96, ...).

Upvotes: 3

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