perl - Perl $$(双美元)符号-它取消引用什么？

Question

我看到了关于Perl $$var -- two dollar signs as a sigil?的问题，该双美元符号用于取消引用

我有这个Perl代码

sub sock_initialize {

    my $sock  = q{};
    my $port  = q{};

    # $name running
    my $max_count   = 250;
    my $timeout     = 5;
    my $max_retries = 36;

    # Get a port for our server.
    $sock = IO::Socket::INET->new(
        Listen    => SOMAXCONN,    # listen queue depth
        LocalPort => 0,
        Reuse     => 1
    );

    die "Unable to bind a port: $!" if !$sock;

    $port      = $sock->sockport();
    my $ip = inet_ntoa( scalar gethostbyname( $HOST ));
    my $uid = (getpwuid( $> ))[2];
    my $queue = join(":", $ip, $port, $$, $uid);

    print sprintf("started on port $port ($$), SOMAXCONN=%d\n", SOMAXCONN);

    return $sock;
} ## end sub sock_initialize

从上面的代码中，双美元符号解引用了什么？ my $queue = join(":", $ip, $port, $$, $uid);

Answer 1

简单地

像bash和其他POSIX下的shell一样: $$是当前进程ID(PID)

对于man perlvar:

  $PROCESS_ID
  $PID
  $$      The process number of the Perl running this script.  Though you can
          set this variable, doing so is generally discouraged, although it can
          be invaluable for some testing purposes.  It will be reset
          automatically across "fork()" calls.

注意:来自 man perl

Reference Manual
        perlsyn             Perl syntax
        perldata            Perl data structures
        ...
        perldebug           Perl debugging
        perlvar             Perl predefined variables
        ...

并从 man POSIX ...

   "getpid"
          Returns the process identifier.  Identical to Perl's builtin
          variable $$, see "$PID" in perlvar.