The awk expression `$0 ~ "regex"` as a bare statement in the action block evaluates the match but doesn't affect the exit code.
awk always prints the line and exits 0, making the validation a no-op.
Bug introduced in b1fa143dd8.
nvm.sh uses `NVM_SCRIPT_SOURCE="$_"` 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.
