问题描述
什么是命令的shell形式和exec形式？
我仔细阅读了几个文档，以清楚地了解shell形式和exec形式。但是所有人都对我感到困惑。任何人都可以帮助找出这两种形式之间的区别吗？
PS ：尽管我在查阅docker文件说明时遇到了这些术语（例如：RUN，CMD，ENTRYPOINT ），我想知道它们之间的一般区别，而不是在Docker上下文中。
What are shell form and exec form of commands?
I have gone through several documents to get a clear idea of shell form and exec form. But all looked confusing to me. Can anyone help to figure out what are the difference between these two form?
PS: Although I came across these terms while I was going through the docker file instructions(ex: RUN, CMD, ENTRYPOINT), I want to know the difference between them in general, not in docker context.
推荐答案
docker shell语法（只是 RUN ， ENTRYPOINT 和 CMD ）将运行该字符串作为 / bin / sh -c 的参数。这使您可以使用Shell来扩展变量，子命令，管道输出，链接命令以及其他Shell便利。
The docker shell syntax (which is just a string as the RUN, ENTRYPOINT, and CMD) will run that string as the parameter to /bin/sh -c. This gives you a shell to expand variables, sub commands, piping output, chaining commands together, and other shell conveniences.
RUN ls * | grep $trigger_filename || echo file missing && exit 1
exec语法只是运行包含的args提供的二进制文件，但是没有任何功能外壳解析。在docker中，您可以使用json格式的数组来表明这一点。
The exec syntax simply runs the binary you provide with the args you include, but without any features of the shell parsing. In docker, you indicate this with a json formatted array.
RUN ["/bin/app", "arg1", "arg2"]
exec语法的优点是从启动的进程中删除了shell，这可能会抑制信号处理。在shell语法中使用 / bin / sh -c 重新格式化命令可能还会破坏入口点和cmd的串联。
The advantage of the exec syntax is removing the shell from the launched process, which may inhibit signal processing. The reformatting of the command with /bin/sh -c in the shell syntax may also break concatenation of your entrypoint and cmd together.
做得很好，涵盖了各种场景并对此进行详细说明。
The entrypoint documentation does a good job covering the various scenarios and explaining this in more detail.
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