$ cat scoping.pl 
#!/usr/bin/env perl 
use strict;
use warnings;


my $data = <<'EOD';

<stlib:mem_bit>72</stlib:mem_bit>
EOD

open my $fh, '<', \$data;

while (my $line = <$fh>) {
    

while ( $line =~ /.*st_mem_bit.*(\d+)/g ) {
    my $num= $1;
    

}
}
print $num;
close $fh;

$ ./scoping.pl 
Global symbol "$num" requires explicit package name at ./scoping.pl line 22.
Execution of ./scoping.pl aborted due to compilation errors.
$