docker - 'set -x' 在 Dockerfile 中有什么作用？

Question

我正在从现有的 Dockerfile 中学习，开始创建自己的 Dockerfile。我注意到大多数时候，命令都以任一开头

RUN set -x ...

或

RUN set -ex; ...

为什么这样做，为什么这是必要的？有必要吗？

Answer 1

-e 使命令在出现任何错误时停止。更典型的语法是用 && 分隔命令以在任何错误时停止。

-x 使shell 输出正在运行的每个命令。这对于调试脚本很有用。

来自 set 下的 bash 手册页:

-e Exit immediately if a pipeline (which may consist of a single simple command), a list, or a compound command (see SHELL GRAMMAR above), exits with a non-zero status. The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test following the if or elif reserved words, part of any com‐ mand executed in a && or || list except the command following the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted with !. If a compound command other than a subshell returns a non-zero status because a command failed while -e was being ignored, the shell does not exit. A trap on ERR, if set, is executed before the shell exits. This option applies to the shell environment and each subshell envi‐ ronment separately (see COMMAND EXECUTION ENVIRONMENT above), and may cause subshells to exit before executing all the commands in the subshell.

If a compound command or shell function executes in a context where -e is being ignored, none of the commands executed within the compound command or function body will be affected by the -e setting, even if -e is set and a command returns a failure status. If a compound command or shell function sets -e while executing in a context where -e is ignored, that setting will not have any effect until the compound command or the command containing the function call completes.

...

-x After expanding each simple command, for command, case command, select command, or arithmetic for command, display the expanded value of PS4, followed by the command and its expanded arguments or associated word list.