echo $$ vs echo $SHELL

"What's running vs. what's configured"

These two variables look similar but answer completely different questions.

echo $$ → “What process am I?”

It gives you the PID (Process ID) of the current shell — a number assigned by the OS to identify the running process. It changes every time a new shell is spawned.

zsh

echo $$     # → 4821

echo $SHELL → “What shell am I configured to use?”

It gives you the path to your login shell as set in /etc/passwd (or your system’s user config). It doesn’t tell you what’s running right now — just what your default is.

zsh

echo $SHELL   # → /bin/zsh

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“You are what you do, not what you say you’ll do.”

— Carl Jung

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