Yashwanth Aluru Yashwanth Aluru - 1 year ago 56
Perl Question

What does $$ in perl actually return?

I'm new to Perl, learning from the beginning. I've read that


The pid of the Perl process running this script.

as per below link,


I've the following Perl Script which is being executed on a Windows machine,

sub test
my ($surrogate_name) = @_;
if((defined $surrogate_name) && ($surrogate_name == 1))
print "Done!"."\n";
return $surrogate_name;

sub t
my ($surrogate_name) = @_;
my $record;
my $surrogate_value;
$record = &test($surrogate_name);
print $record."\n";
if ($record)
print "B"."\n";
$surrogate_value = $$record{$surrogate_name};
print $surrogate_value."\n";
print "A"."\n";
return $surrogate_value;


In this code, I observed everything is printed except the value of

Please clarify me what does
actually mean and why it's not returning anything in my script.

Thanks in advance...

Answer Source

Yes $$ returns the process id of currently running script.

but in your case $surrogate_value = $$record{$surrogate_name} which is completely different concept that is a dereferencing.

for example $$ used along with a variable name to dereference it.

my $a = 10; #declaring and initializing a variable.
my $b = \$a; #taking scalar value reference
print $$b;  #now we are dereferencing it using $$ since it is scalar reference it will print 10

my %hashNew = ("1" => "USA", "2" => "INDIA"); #declaring a hash
my $ref = \%hashNew; #taking reference to hash
print $$ref{2}; #this will print INDIA we derefer to hash here

For more understanding read referencing and dereferencing in perl.

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