Use a dispatch table, a hash with your commands as keys and code references as values,

my %dispatch = (
    start => sub {
        my @args = @_;
        # . . .
    },
    # . . .
);

while (<STDIN>) {
    my ($cmd, @args) = split;
    exists $dispatch{$cmd}
        or warn 'Unknown command: ', $cmd and next;
    $dispatch{$cmd}(@args);
}
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