x-prefix in comparisons no longer serves a purpose

do

@@ -1,8 +1,10 @@
 #!/bin/sh
-export PATH=$HOME/.cargo/bin:$PATH
-CARGO=$(command -v cargo)
+
 set -e
-if test "x$CARGO" = "x"; then
+export PATH="$HOME/.cargo/bin:$PATH"
+CARGO="$(command -v cargo)"
+
+if [ -z "$CARGO" ]; then
     printf "Rust & Cargo are required in order to build cjdns\n"
     printf "See https://rustup.rs/ for install instructions\n"
     exit 1
@@ -14,6 +16,9 @@ if echo "$@" | grep -q '\-\-debug'; then
     path="debug"
 fi 
 RUSTFLAGS="$RUSTFLAGS -g" $CARGO build $release
-RUST_BACKTRACE=1 ./target/$path/testcjdroute all >/dev/null
-mv ./target/$path/cjdroute ./target/$path/cjdnstool ./
+RUST_BACKTRACE=1 "./target/$path/testcjdroute" all >/dev/null
+if ! mv -- "./target/$path/cjdroute" "./target/$path/cjdnstool" ./; then
+  printf "Cannot find executables at %s\n" "./target/$path"
+  exit 1
+fi
 printf "\x1b[1;32mBuild completed successfully, type ./cjdroute to begin setup.\x1b[0m\n"