Signal handling varies greatly from OS to OS, and you don't mention what you're running on, but I'll take a stab at it.

The problem is that you're trying to call the routine from the signal handler. In turn, that routine expects to continue to receive SIGALRM, although in most cases, the signal won't be delivered while you're in the handler (otherwise the handler might get called recursively).

A better strategy would be to let the handler throw an exception, and then let the outer loop control the logic. Here's a modification of your program that does what (I think ;-) you want.

#!/usr/bin/perl -w
$SIG{ALRM} = sub { die "timeout"; };

while (1) {
    eval { command(); };

    if ($@) {
         if ($@ =~ /timeout/) {
             redo;
         } else {
             alarm(0);
             die;
         }
   }
   else {
        last;
   }
}

print "Done\n";

sub command {
        my $date = `date`;
        chomp($date);
        alarm(5);
        print "\n";
        print "prompt $date > ";
        <>;
        alarm(0);
}
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HTH. The usual disclaimers apply: I'm not sure exactly what behavior you wanted, nor what OS you're on, yada, yada, yada.

But note that for Win32 IO::Select won't work for STDIN. ;-/

#!/usr/bin/perl
use strict;
use warnings;
use Term::ReadKey;

sub timed_input {
   my $end_time = time + shift;
   my $string;
   do {
       my $key = ReadKey(1);
       $string .= $key if defined $key;
   } while (time < $end_time);
   return $string
};

my @words = split ' ', timed_input(10);
print "@words\n";
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I am trying zentaras snippet, and failing...

my perl script got started as a child process, so the parent communicates via STDIN to my script. There is no real keyboard involved. Unfortunately I'm not really up to speed on terminals and tty. I'm wondering if Term::ReadKey should work in that case.

This is a win32 application

sub get_stdin_w_timeout {
  ######!/usr/bin/perl
  #got from zentara on perl monks in response to Timeout on STDIN
  #modifying to use ReadKey to get first key and then <STDIN> to get t
+he rest of the line
  #this function assumes that once there is some input on stdin,
  #the rest of the line is available too
  use strict;
  use warnings;
  use Term::ReadKey;
  my $timeout_in_sec=shift;
  my $end_time = time + $timeout_in_sec;
  my $key="";
  do {
    my $key = ReadKey(1);
    if (defined $key) {
      #not sure if I need to concatenate $key on the front of <STDIN>
      return $key. <STDIN>;
    }
    
  } while (time < $end_time );
  return "!ERROR!:Timed out waiting on input after ${timeout_in_sec}s\
+n";

}
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when i run this like this

    $plibMsg=&get_stdin_w_timeout(5);#<STDIN>;
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I always get the Timed out message

No experience of my own, but the reply to Problems with Term::ReadKey suggests that you might have to set

$| = 1;
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for STDIN.