use strict;
use warnings;
use 5.010;

eval {
    local $SIG{ALRM} = sub {die "my timeout"};  
    #execute this sub when ALRM signal received

    alarm 3;  
    #sends ALRM signal to this process in 3 secs, which causes sub 
    #to execute

    $| = 1;   
    #turn off buffering to STDOUT, otherwise all output will come at
    #program termination when STDOUT's buffer is automatically 
    #flushed

    while (1) {
      say 'hi';
      sleep 1;
    }
};  #<-- don't forget that semi-colon

--output:--
hi
hi
hi