I have a very simple regex task that has left me confused (and just when I thought I was starting to get the hang of them too). I just want to check that a string consists of 11 digits. The regex I have used for this is /\\d{11}/
. My understanding is that this will give a match if there are exactly (no more and no less than) 11 numeric characters (but clearly my understanding is wrong).
Here is what happens in irb:
ruby-1.9.2-p136 :018 > "33333333333" =~ /\d{11}/
=> 0
ruby-1.9.2-p136 :019 > "3333333333" =~ /\d{11}/
=> nil
ruby-1.9.2-p136 :020 > "333333333333" =~ /\d{11}/
=> 0
So while I get an appropriate match for an 11 digit string and an appropriate no-match for a 10 digit string, I am getting a match on a 12 digit string! I would have thought /\\d{11,}/
would be the regex to do this.
Can anyone explain my misunderstanding?
Without anchors , the assumption "no more, no less" is incorrect.
/\d{5}/
matches
foo12345bar
^
+---here
and
s123456yargh13337
^^ ^
|+---here |
+----here |
here--+
So, instead use:
/^\d{5}$/
The 12 digit string contains the substring that matches your regexp. If you want an exact match, write the regexp like this: /^\\d{11}$/
.
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