defining a Command and Arguments for a Container 給容器定義一個命令和參數。
This page shows how to define commands and arguments when you run a container in a Kubernetes Pod. 這篇文章展示當運行kubernetes pod的時候，如何給容器定義命令和參數。
When you create a Pod, you can define a command and arguments for the containers that run in the Pod. To define a command, include the command field in the configuration file. To define arguments for the command, include the args field in the configuration file. The command and arguments that you define cannot be changed after the Pod is created. 當創建Pod的時候，我們可以給這個Pod中的容器定義命令和參數。 定義命令，需要在配置文件中加入command標簽。為這個命令定義參數，需要加入args標簽。當Pod創建好了以后，定義好的命令和參數不可以被變更和修改。
The command and arguments that you define in the configuration file override the default command and arguments PRovided by the container image. If you define args, but do not define a command, the default command is used with your new arguments. For more information, see Commands and Capabilities. 如果在容器的鏡像中定義了命令和參數，那么如果在配置文件中再次定義，則鏡像中定義的命令和參數會被覆蓋。如果只定義了參數，沒有定義命令，那么默認的命令會使用新定義的參數。更多的信息，查看Commands和Capabilities.
In this exercise, you create a Pod that runs one container. The configuration file for the Pod defines a command and two arguments: 在這個練習中，會創建一個運行了一個容器的Pod。在配置文件中配置的Pod定義了一個命令和兩個參數： commands.yaml
apiVersion: v1kind: Podmetadata: name: command-demo labels: purpose: demonstrate-commandspec: containers: - name: command-demo-container image: debian command: ["printenv"] args: ["HOSTNAME", "KUBERNETES_PORT"]Create a Pod based on the YAML configuration file:通過yaml配置文件創建Pod: kubectl create -f http://k8s.io/docs/tasks/configure-pod-container/commands.yamlList the running Pods:查看運行的Pods: kubectl get podsThe output shows that the container that ran in the command-demo Pod has completed.輸出可以查看到容器已經在command-demo pod中已經完成。To see the output of the command that ran in the container, view the logs from the Pod:查看容器的輸出結果，輸出Pod的日志： kubectl logs command-demoThe output shows the values of the HOSTNAME and KUBERNETES_PORT environment variables:輸出顯示出HOSTNAME和KUBERNETES_PORT兩個環境變量的值 command-demo tcp://10.3.240.1:443Using environment variables to define arguments 使用環境變量來定義參數 In the preceding example, you defined the arguments directly by providing strings. As an alternative to providing strings directly, you can define arguments by using environment variables:
env: - name: MESSAGE value: “hello world” command: [“/bin/echo”] args: [“$(MESSAGE)”]
This means you can define an argument for a Pod using any of the techniques available for defining environment variables, including ConfigMaps and Secrets.
NOTE: The environment variable appears in parentheses, “$(VAR)”. This is required for the variable to be expanded in the command or args field. Running a command in a shell
In some cases, you need your command to run in a shell. For example, your command might consist of several commands piped together, or it might be a shell script. To run your command in a shell, wrap it like this:
command: [“/bin/sh”] args: [“-c”, “while true; do echo hello; sleep 10;done”]
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