$_
nvm.sh
nvm.sh uses `NVM_SCRIPT_SOURCE="$_"` to detect its source location. Adding `: nvm.sh` before each source line ensures `$_` is set correctly, preventing breakage when the previous command (e.g., `set -ex`) overwrites it.
This restriction prevents subcommands from producing colors and passing them up the tree to the actual TTY.
nvm_ensure_default_set