What is the meaning of $$ in Ruby?

irb(main):002:0> $$
=> 5052

What is the meaning of `$$` in Ruby and How/Where to use it?

[This][1] seems like a good reference for stuff like this...has a lot of symboly goodness.

[1]:

[To see links please register here]

`$$` is the [process ID](

[To see links please register here]

). It's named that way to follow Perl, which in turn followed the Bourne shell; both of them also use `$$` in the same way.

pipe = IO.popen("")
if pipe
STDERR.puts "In parent, child pid is #{pipe.pid}"
else
STDERR.puts "In child, pid is #{$$}"
end

This example shows how the process ID can be used. Process ID is part of 'Execution Environment Variables' (part of predifined variables).

It's the process ID of the current Ruby process. Read-only

It's the process ID of the Ruby interpreter. $ is a prefix for global variables, see [here][1] for a list.


[1]:

[To see links please register here]