Here is my non-regex solution. It's long, ugly and not very efficient but it works!

my ($page) = "12345abc67890";

print &get_page_chunk('12345','67890',$page);

sub get_page_chunk {
    
    my ($start_marker,$end_marker,$page) = @_;
    
    my ($x1,$x2) = -1;
    
    $x1 = index($page,$start_marker);
    
    if ($x1 != -1) {
        
        $x1 += length($start_marker);
        $x2  = index($page,$end_marker,$x1);
        
        if ($x2 != -1 && $x2 > $x1) {
            
            return(substr($page,$x1,$x2-$x1));
            
        };
        
    };

    return ('');
    
};
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