my $pid = fork;
die "can't fork: $!" if ! defined $pid;
if ( $pid ) {
    # parent
}
else {
    # child
}

##</code><code>##

use 5.010;

my $pid = fork // die "Can't fork: $!";
if ...

##</code><code>##

use 5.010;

given ( fork ) {
    when ( undef ) {
        die "Can't fork: $!";
    }
    when ( !$_ ) {
        # child
    }
    default {
        # parent
        my $child_pid = $_;
    }
}

##</code><code>##

use 5.010;

given ( wantarray ) {
    when ( undef ) {
        return;           # void context
    }
    when ( !$_ ) {
        return 'scalar context';
    }
    default {
        return qw( list context );
    }
}

##</code><code>##

return         wantarray ? qw( list context ) :
       defined wantarray ? 'scalar context';

##</code><code>##

return tfu( wantarray,
            true  => sub { 'true' },
            false => sub { 'false' },
            undef => sub { 'undef' }, );

sub tfu {
    my $value = shift @_;
    my %todo_for = @_;

    return         $value ? $todo_for{ true }->()  :
           defined $value ? $todo_for{ false }->() :
                            $todo_for{ undef }->();
}