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Match multiple number

by IB2017 (Pilgrim)
on Aug 17, 2018 at 18:37 UTC ( #1220530=perlquestion: print w/replies, xml ) Need Help??

IB2017 has asked for the wisdom of the Perl Monks concerning the following question:

Dear monks

How can I write the following regex so that it matches ad infinitum all numbers that are x=x+5? In my regex I stopped at 25.

if ($Number=~/0|5|10|15|20|25/){ ... }

Replies are listed 'Best First'.
Re: Match multiple number
by tobyink (Canon) on Aug 17, 2018 at 18:45 UTC

    Use modulo arithmetic.

    if ($Number % 5 == 0){ ...; }

    Alternatively, as all multiples of five end in a 5 or a 0, you can do something like this:

    if ($Number =~ /^-?[0-9]*[05]$/){ ...; }

    In both these cases, I'm allowing negative values, like -5 and -10. If you prefer to only allow non-negative values:

    if ($Number % 5 == 0 and $Number >= 0){ ...; }
    if ($Number =~ /^[0-9]*[05]$/){ ...; }

      Thank you very much. I like these solutions.

Re: Match multiple number
by davido (Cardinal) on Aug 17, 2018 at 22:21 UTC

    Totally useless but a little bit of fun with a silly mathematical property:

    #!/usr/bin/env perl + + use strict; + use warnings; + use List::Util qw(sum); + + # For each $n, convert $n to hex digits, add the digits together. If t +he # result has more than one hex digit, repeat this process adding the + # digits together. When there is only one hex digit remaining, if the + # digit is a '5', an 'a', or an 'f', the original number was divisible + # by 5. + + for my $n (1..100) { + my $h = sprintf '%x', $n; + while(length($h) > 1) { + $h = sprintf '%x', sum(map {hex $_} split //, $h); } + print "$n is a multiple of 5\n" if $h =~ m/^[5af]$/; + }

    Output:

    5 is a multiple of 5 10 is a multiple of 5 15 is a multiple of 5 20 is a multiple of 5 25 is a multiple of 5 30 is a multiple of 5 35 is a multiple of 5 40 is a multiple of 5 45 is a multiple of 5 50 is a multiple of 5 55 is a multiple of 5 60 is a multiple of 5 65 is a multiple of 5 70 is a multiple of 5 75 is a multiple of 5 80 is a multiple of 5 85 is a multiple of 5 90 is a multiple of 5 95 is a multiple of 5 100 is a multiple of 5

    Dave

      Interesting. I guess this works for the same reason it does with 3 in decimals.

Re: Match multiple number
by jwkrahn (Monsignor) on Aug 17, 2018 at 18:47 UTC
      my $Number = '!56'; if ( $Number =~ /\d*[05]/ ) { say "$Number is divisible by 5."; warn 'Really?'; }

      A dollar sign missing somewhere at least.

      ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord }map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
Re: Match multiple number
by dbuckhal (Hermit) on Aug 19, 2018 at 00:06 UTC

    Another similar solution:

    $ perl -e ' for (0..1000) { my $n = int(rand(10000)); print $n, "\n" if $n =~ /\d{0,}[05]\z/ } ' __sample_output__ 7495 8120 8340 9540 7370 4455 310 7540 35 7085 7235 5355 9190 6790 1360 820 1900 1945 1630 9895
        yeah, but it satisfies the OP's implied set of integer values given by x=x+5 | {0, 5, 10, 15, 20, 25, ...}

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