perldoc -f alarm

#!/usr/bin/perl
$lines=0;
eval {
  local $SIG{ALRM} = sub { die "timeout\n" };
  alarm( 5 );
  while (<>) {
    $lines++;
    if ( $lines > 2 ) {
      alarm( 0 );
      last;
    }
  }
};
if ( $@ =~ /timeout/ ) {
  print "timed out with $lines lines\n";
}
elsif ( $@ ) {
  print "died from some other random reason: $@";
}
else {
  print "didn't timeout with $lines lines\n";
}
[download]

$ ( sleep 10 ) | perl 409100.pl 
timed out with 0 lines

$ ( echo one; sleep 10 ) | perl 409100.pl 
timed out with 1 lines

$ ( echo one; echo two; sleep 10 ) | perl 409100.pl 
timed out with 2 lines

$ ( echo one; echo two; echo three; sleep 10 ) | perl 409100.pl 
didn't timeout with 3 lines
[download]