Try this.

eval {

        local $SIG{'ALRM'} = sub { die "timed out\n" };

        alarm(10);
        system("sleep 30; echo 'I made it'") && die "system call faile
+d\n";
        alarm(0);

};
if ($@) {
        if ($@ eq "timed out\n") {
                print "I timed out\n";  
        }
        else {
                print "something else went boom\n";
        }
}
else {
        print "I didn't time out\n";
}
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In ten seconds you should get output that reads "I timed out". This is almost exactly the eval timeout out example from the 'perlfunc' perldoc page. I modified it a little to have print statements for what happened where.

/\/\averick

Updated:

bluto is quite right. here is my updated code. This seems to work fine under Linux. The only problem I have with Dominus solution is requiring the external program (you should be able to get it to work in one piece of code IMHO ;) )

-- first.pl -- 
#!/usr/bin/perl

use strict;

my $pid;
eval {

        local $SIG{'ALRM'} = sub { die "timed out\n" };

        alarm(10);

        $pid = fork;
        if ($pid == 0) {
                exec("./second.pl");
        }
        else {
                wait;
        }

        alarm(0);

};
if ($@) {
        if ($@ eq "timed out\n") {
                kill(15,$pid);
                print "I timed out\n";  
        }
        else {
                print "something else went boom\n";
        }
}
else {
        print "I didn't time out\n";
}

-- second.pl -- 
#!/usr/bin/perl

while(1) {
        print "alive\n";
        sleep(1);
}
[download]

This produces this output on my system.

darkstar:~>./first.pl 
alive
alive
alive
alive
alive
alive
alive
alive
alive
alive
I timed out
darkstar:~>
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