There's two ways I can think of to do it - one is via threading your perl, to make your 'reading STDIN' run in parallel. Something like:

#!/usr/bin/perl

use strict;
use warnings;

use threads;

use Thread::Queue;

my $input_q = Thread::Queue -> new();

sub stdin_reader
{
  while ( my $line = <STDIN> ) 
  {
    if ( defined $input_q -> pending() )
    {
      $input_q -> enqueue ( $line );
    }
    else
    {
      last;
    }
  }
}

sub doing_stuff_thread
{ 
  my $count = 0;
  while ( $count < 10 )
  {
    my $item = $input_q -> dequeue_nb();
    if ( defined $item )
    {
      print "Got: $item";
      $count++;
    }
    else
    {
      print "Doing something else, because nothing on STDIN\n";
      print "Pending items:", $input_q -> pending(), "\n";
      sleep 1;
    }
  }
  $input_q -> end(); 
}

threads -> create ( \&stdin_reader );
threads -> create ( \&doing_stuff_thread );

foreach my $thr ( threads -> list() )
{
  print "Waiting for ",$thr -> tid()," to join\n";
  $thr -> join();
}
[download]

That works, although bear in mind that 'STDIN' is being read line by line, so you need to put carriage returns in. (you can't do 'readkey' style). (And also - you may find 'Thread::Queue' isn't 'standard', but I'm sure you can figure out how to do something useful with thread::shared and lock instead.

The other way I can think of involves using IO::Select. Or perhaps like this node: Here

#!/usr/bin/perl

use strict;
use warnings;

use IO::Handle;
use IO::Select;

my $nb_stdin = new IO::Select( *STDIN );

while ( 1 )
{
  if ( $nb_stdin -> can_read(0) )
  {
    my $line = <STDIN>;
    print "Got: ", $line,"\n";
  }
  else
  {
    print "Nothing on STDIN, doing something else\n";
    sleep 1;
  }
}
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This doesn't seem to work properly on Win32/Activestate though - I believe I've seen something to the effect that IO::Select doesn't work on non-sockets on W32. YMMV