I think you mean that you want to loop "non-blocking", meaning that you want to continue processing even if there is no user input. To do that, one usually uses 4-arg select, or the OO-wrapper interface IO::Select. Here's a trivial example to get you started.

use IO::Select;

# loop every 1 second
my $timeout = 1;

my $s = IO::Select->new();
$s->add(\*STDIN);

while ( 1 )
{
    if ( my @ready = $s->can_read($timeout) )
    {
        # we got input

        for my $fh ( @ready )
        {
            my $input = <$fh>;
            print "got: $input";
        }
    }
    else
    {
        # no input
    }

    # just to show that we're looping
    print scalar localtime;
}
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Update: I just remembered what select says about mixing buffered reading and "select", so even though the above code works, you might want to substitute the read via <$fh> with:

my $input;
sysread( $fh, $input, 1024);
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