error $GOPATH: no library found in $GOPATH: rdkafka

安装confluent-kafka-go出错时，请使用brew安装pkg-config，手动go get安装的pkg-config还不行。。。

错误提示：

go get -u github.com/confluentinc/confluent-kafka-go/kafka


# pkg-config --cflags  -- rdkafka
error $GOPATH: no library found in $GOPATH: rdkafka
error github.com: PKG_CONDIF_GITHUB not exported, skipping github.com lookup
error $PKG_CONFIG_PATH: open rdkafka.pc: no such file or directory
error <autogenerated>: no library found in $GOPATH: rdkafka
pkg-config: exit status 1

解决：

brew install pkg-config