It sounds like you want to add STDIN to IO::Select. When STDIN is readable, it will run the callback which will read everything it can. I didn't write the following, fellow monk edan did, but I'll post it in case he is out golfing or something. :-)

#!/usr/bin/perl
use warnings;
use strict;
use IO::Select;

# by edan of perlmonks 
# I just remembered what select says about mixing  
# buffered reading and "select", so even though the
# code works, you might want to substitute  
# the read via <$fh> with: 
#    my $input; 
#    sysread( $fh, $input, 1024); 


# 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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