When the command echo $$ outputs 12942, what is the meaning of 12942?

Question

Options

• AIt is the process ID of the echo command.
• BIt is the process ID of the current shell.
• CIt is the process ID of the last command executed.
• DIt is the process ID of the last command which has been placed in the background.

• A
  7% (4)
• B
  79% (44)
• C
  13% (7)
• D
  2% (1)

Explanation

$$ is a special shell variable that always holds the process ID (PID) of the current shell itself - so 12942 is the PID of the running shell session that executed the command.

Why the distractors are wrong:

• A is wrong because echo runs as a child process with its own distinct PID; $$ is evaluated by the shell before echo even spawns.
• C is wrong - that's $?, which holds the exit status (not PID) of the last command; there is no built-in variable for the PID of the last foreground command.
• D is wrong - $! holds the PID of the most recently backgrounded job, not $$.

Memory tip: Think of $$ as the shell asking "who am I?" - the double dollar sign refers to itself. Pair it with $! ("last background job") and $? ("last exit status") as the three most common special variables to know.

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