`$()` creates a subshell (a whole separate process) so is significantly slower than mere string manipulation. `$PWD` is always set accurately at startup (for b

`$()` creates a subshell (a whole separate process) so is significantly slower than mere string manipulation. `$PWD` is always set accurately at startup (for both interactive and non-interactive shells) in bash, dash, zsh, ksh93, mksh, and busybox ash. So I'm really not sure where this assumption can be violated.