Re: regex not working

[jwkrahn]

Well let's see what your program does:

$ perl -le'
use warnings;
use strict;

print "Enter number : ";
chomp( my $num = <STDIN> );
print "\$num = $num";

my @nums = split /(?<=[\d])/, $num;
print "\@nums = @nums";

my $i = 0;
for ( @nums ) {
    my $regex = qr/[$i]{$_}/;
    print "\$regex = $regex";
    print $num =~ $regex ? "true" : "false";
    $i++;
    }
'
Enter number : 
2020
$num = 2020
@nums = 2 0 2 0
$regex = (?-xism:[0]{2})
false
$regex = (?-xism:[1]{0})
true
$regex = (?-xism:[2]{2})
false
$regex = (?-xism:[3]{0})
true

On the first pass you are trying to match '2020' with /[0]{2}/, or in other words with /00/.    Since '2020' does not contain the string '00' the program prints false.

On the second pass you are trying to match '2020' with /[1]{0}/, or in other words with //.    Since '2020' contains five places that will match the program prints true.

$ perl -le'$x = () = "2020" =~ /[1]{0}/g; print $x'
5

The next two follow the same pattern as the first two.