my $split_pattern = ' ';

##</code><code>##

my @x = split $split_pattern, $line;

##</code><code>##

my $split_pattern;
...
my @x = defined($split_pattern)
        ? split $split_pattern, $line
        : split ' ', $line;

##</code><code>##

my @x = split defined($split_pattern)?$split_pattern:' ', $line;