Your expectation does not meet the specification, unless you are using the heptadecimal notation.

You can use index to find a substring in a string. Its third argument tells Perl where to start searching.

#!/usr/bin/perl
use warnings;
use strict;

my $input = "471234973798375754773971832374974447889743725345932";
my $pos   = 0;
while (-1 != ($pos = index $input, '47', $pos)) {
    print substr($input, $pos++, 10), "\n";
}
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