Alarm has only recently been implemented on Win32, and it still seems to have some limitations.

Here's another way of achieving this that should be portable back to at least 5.6.1.

#! perl -slw
use strict;

sub systemWithTimeout {
    my( $timeout, $command ) = @_;
    my $pid = open my $in, "$command |" or die $!;
    my $endtime = time() + $timeout;
    Win32::Sleep 100 while time() < $endtime and kill 0, $pid;
    Win32::Sleep 0; ## Give the other process a timeslot to go away
    my $wasKilled = kill 9, $pid if kill 0, $pid;
    return wantarray ? ( $wasKilled , <$in> ): $wasKilled;
}

for ( 4 .. 6 ) {
    print "5 second timeout on a process that runs for $_ seconds";
    my( $timeout, @results ) = systemWithTimeout 5,
        qq[ perl -wle" sleep $_; print $$, ' ', scalar localtime;" ];

    printf "The process %s timeout\n", $timeout ? 'did' : 'did not';
    print "it returned\n @results" if @results;
}

print "\nscalar context";
if( systemWithTimeout 5, qq[ perl -wle" sleep 3; print for 1 .. 100" ]
+ ) {
    print "command timed out";
}
else {
    print "command completed";
}

if( systemWithTimeout 5, qq[ perl -wle" sleep 7; print for 1 .. 100" ]
+ ) {
    print "command timed out";
}
else {
    print "command completed";
}

__END__
C:\test>539889
5 second timeout on a process that runs for 4 seconds
The process did not timeout
it returned
 1896 Wed Mar 29 11:50:25 2006

5 second timeout on a process that runs for 5 seconds
The process did not timeout
it returned
 1896 Wed Mar 29 11:50:31 2006

5 second timeout on a process that runs for 6 seconds
The process did timeout

scalar context
command completed
command timed out
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