emichswimr has asked for the wisdom of the Perl Monks concerning the following question:

I want to specify a certain number of digits to match. ex. a zip code has 5 digits, 48197 $zip =~ /\d{5}/ while this will make sure that there is 5 digits it will also accept 6 digits. Suggestions?

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Re: specific numbers of digits
by pg (Canon) on Mar 19, 2003 at 05:07 UTC
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Re: specific numbers of digits
by Limbic~Region (Chancellor) on Mar 19, 2003 at 19:05 UTC
    emichswimr,
    If you know that your input string will only be a sequence of digits, then use pg's solution of anchoring with ^ and $. If you need to match within a string, then one of these may help. 

    /\b\d{5}\b/;
or
/\D\d{5}\D/;
or
/\s+\d{5}\s+/;

    [download]
  • The first one breaks on word boundaries (any character not in \w)
  • The second one breaks on any non digit
  • The third one breaks on white spaces

    Cheers - L~R

    Update: Changed introduction to explain why these solutions may be more flexible then the ones that anchor with ^ and $

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Re: specific numbers of digits
by pfaut (Priest) on Mar 19, 2003 at 12:28 UTC

    Add a negative lookahead assertion to make sure the next character is not a digit: /\d{5}(?!\d)/ 

    ---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';

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      That will still match 6 digits, it'll just match the last 5 rather than the first 5. To match only 5 digits you need an assertion at both ends:

        m{
    (?>! \d)  # not after a digit
    \d(5}
    (?! \d)   # not before a digit
  }x;

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      Hugo
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Re: specific numbers of digits
by lacertus (Monk) on Mar 19, 2003 at 04:33 UTC
    Put an upper limit on that match, say you want between 5 and 7 digits: 
    my $ID = 0123456;
if ($ID =~ /\d{5,7}/ {
    do this...
}

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    So for your case, perhaps /\d{5,5}/
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      This does not meet his requirement, as your regexp still matches 6-digit strings i.e. your regexp still matches strings like "123456".

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Re: specific numbers of digits
by MZSanford (Curate) on Mar 19, 2003 at 14:11 UTC
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      Sorry to point this out, but..

      $x = "123456";
if ( $x =~ /\d{5,5}/ ) {
   print "wrong";
   }

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      Still matches 123456

      This will do the trick

      $x = "123456";
if ( $x =~ /^\d{5}$/ ) {
   print "right";
   }

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