LFCS Question #2: Real Exam Question with Answer & Explanation

Question

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

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.

Explanation

The special shell variable $$ expands to the process ID (PID) of the shell instance that is currently executing the command.

Common mistakes.

• A. The $$ variable does not represent the process ID of the echo command itself; echo runs as a child process and would have a different PID.
• C. The $$ variable specifically refers to the current shell's PID, not the PID of the last command executed, which would typically be a different value.
• D. The $$ variable refers to the current shell's PID, while the PID of the last command placed in the background is stored in the $! variable.

Concept tested. Shell special variable $$ (current shell PID)

Reference. https://www.gnu.org/software/bash/manual/bash.html#Special-Parameters

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