What jethro said: Only fork if you need to do something in both processes.

If that's the case, here is a working example:

#!/usr/bin/env perl

use 5.014;
use strict;
use warnings;

my $pid = fork;

if (!defined $pid) {
    die "Cannot fork: $!";
}
elsif ($pid == 0) {
    # client process
    say "Client starting...";
    sleep 10; # do something useful instead!
    say "Client terminating";
    exit 0;
}
else {
    # parent process
    say "Parent process, waiting for child...";
    # do something useful here!
    waitpid $pid, 0;
}
say "Parent process after child has finished";
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One thing to note is that fork returns undef on failure, and undef == 0 compares as true, so your error handling wouldn't work. To easily test the error case, start a new bash and set ulimit -u $number_of_allowed_processes, then start the perl script.