What is the meaning of $$1 in bash?

Solution 1:

$$ is the PID (process id) of the current process.

$$1 is the above PID followed by the literal string 1.

So it is telling you that your bash is the process with PID 1930.

But... free trick:

show() { eval echo \$$1; }
show PATH
/home/romano/bin:/usr/local/bin:/bin:/usr/bin

(quite convoluted, ain't it?)

More info in TLDP.

Solution 2:

• $$ - pid of the current shell (not subshell) - see What are the special dollar sign shell variables?

• $$1 - pid of the current shell (not subshell) followed by 1.

• $$2 - pid of the current shell (not subshell) followed by 2.

• $$a - pid of the current shell (not subshell) followed by a character.

• And so on...

See the output of echo $$1.

And you get the error command not found because you are trying to execute a string composed of digits which obviously is not a command.

Solution 3:

You have concatenated $$ and 1 together to get the PID of the current shell and 1, i.e. $$ stands for the PID of the currently running shell and 1 is just a character, you could do $$a, $$@ to get the PID concatenated with the following character.