You want an alarm, however with backticks this does leave the process hanging and there's no easy way to get its pid, but it is your child so you can do things to your process group to take it down, perhaps an END that sigkills the process group?

eval {
    local $SIG{ALRM} = sub { die "Alarma" };

    alarm 10;
    `perl -e 'while(1) {};'`;
    alarm 0;
};

if ($@ eq 'Alarma') {
    warn "alarm'd";
} elsif ($@) {
    die $@;
}
[download]

Thanks guys. Now I'm noticing though that when I do this, the process continues running. How can I be sure to terminate this process?



> cat perl.pl
#!/usr/bin/perl

eval {
  $SIG{ALRM} = sub { die "Timed out\n"; };
  alarm(5);
  `perl -e 'while(1){sleep 1;}'`;
  alarm(0);
};
print "Died with: $@\n";

> ./perl.pl
Died with: Timed out

> ps
  PID TTY          TIME CMD
11551 pts/0    00:00:00 bash
11648 pts/0    00:00:00 perl
11651 pts/0    00:00:00 ps
[download]

You're probably better off using piped open (see perlopentut) in this case, since that will give you the process id of the spawned process:

# set up alarm...
my $pid;
$SIG{ALRM} = sub { kill $pid; die "Timed out" };
alarm(5);
$pid = open PROG,"/some program|" or die "Can't fork: $!";
my $input = join('',<PROG>);
alarm(0);
close PROG;
[download]

Note; code is untested.

update: added alarm() calls.

"What should it profit a man, if he should win a flame war, yet lose his cool?"

use strict;
use warnings;
 
my $timeout = 3;

eval {
    local $SIG{ALRM} = sub { die "alarm\n" };
    alarm $timeout;
    `perl -e "while(1) { }"`;
    alarm 0;
};

if ($@) {
   die "DID timeout after $timeout second(s)\n";
}

print "never see this text\n";
[download]

No simple portable way. I've done this on both Unix and Windows and chose a different technique on each. Reading the responses to Threads or no Threads should prove useful: there are a couple of nice ideas from ikegami along with links to the Unix and Windows solutions I wrote.