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How to use Regular Expression to check for minimum string length

Posted on 2004-10-07
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Last Modified: 2012-05-05

Hi,

How do I use a Regular Expression to find out  if a string is at least N characters?

Thanks.
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Question by:l_agmon
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8 Comments
 
LVL 16

Expert Comment

by:manav_mathur
ID: 12247276
/^.{5}$/

or

/^.....$/



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LVL 16

Expert Comment

by:manav_mathur
ID: 12247284
Sorry didnt read 'atleast'.

/^.{5}.*
/^......*$/    (remember to put 6 dots, * stands for any number of including 0)
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LVL 16

Expert Comment

by:manav_mathur
ID: 12247311
Im sorry, was in a bad state while replying, so assumed it as 5.

/^.{N}.*/   replace N with the number of characters. AFAIK, you cannot use a variable here in a $ format.

second option is
/^......*/  - but do remember to put N+1 dots. This is because * works on the last dot and it means, any number of any character including zero characters. . so N dots means N characters and follow it by a .* for any number of characters including zero. So the whole thing reads like, N characters followed by any number of characters.....

Cheers,
Manav
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LVL 6

Accepted Solution

by:
DominicCronin earned 125 total points
ID: 12260603
Of course, the correct answer to your question depends on which regex language you are using. It's not uncommon for a regex language to allow you to specify "both ends"  of an interval quantifier. Using several dots is one possibility, but let's assume Perl regexes for a moment. The interval quantifier allows you to say {n,m} meaning match n to m times. This means that

.{5,}

will match at least 5 characters. In perl this would look like:

/.{5,}/

Note that manav's use of anchors (^ and *) isn't necessary if all you want to do is check that the string is at least that long. Still - I suppose you want to make this part of some more complicated test. Using regexes just to check a string length is overkill. Most programming languages (all programming languages??) have simpler ways to get the length of a string.
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LVL 6

Expert Comment

by:DominicCronin
ID: 12477505
I think the correct answer is "you shouldn't". Anyway - sufficient good suggestions have been given to award the points and PAQ the question.
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