External command vs built-in

External command new process · shell unchanged

~/project

❯

v24.13.0

~/project

Shell zsh · pid 501

cwd ~/project

built-in?

$PATH

fork + exec

Kernel processes

501 zsh running

502 node running

Built-in command no new process · shell changed

~/project

❯

~/project/src

❯

Shell zsh · pid 501

cwd ~/project

built-in?

$PATH

chdir("src")

Kernel processes

501 zsh running

no new process

A child process can't reach back into its parent — so anything that changes the shell has to run inside it. illustrative pids