为什么不“回声"?出现在"ps"中? [英] Why doesn't "echo" show up in "ps"?

问题描述

我很难理解ps命令中显示的内容.为了测试我的理解，我在虚拟脚本下创建了

I am having great difficulty in understanding what shows up on ps command. To test my understanding I created below dummy script

 #!/bin/bash
 for i in {1..100000}
 do
  date -u
  date -u
  date -u
 done

运行此脚本时，我打开了一个新终端并重复执行

while running this script I opened a new terminal and executed repeatedly

ps -eaf | grep date | grep -v grep

并且我能够在输出中确定过程的日期.

and I was able to date process in the output.

我后来通过将 date -u 替换为 echo正在发生什么事情"

     #!/bin/bash
     for i in {1..100000}
     do
      echo "What is going on"
      echo "What is going on"
      echo "What is going on"
     done

在运行更新的虚拟脚本时，我打开了一个新终端并重复执行

while running the updated dummy script, I opened a new terminal and executed repeatedly

ps -eaf | grep echo | grep -v grep

，并且在输出中从未显示回声.为什么是这样?我怀疑原因是该脚本是bash脚本，可能是由于使用内置回显，因此未在ps输出中显示.我对么?我在这里想念什么?

and echo was never shown in output. Why is this? I suspect the reason is the script being a bash script, may be it is using builtin echo therefore it was not displayed in ps output. Am I correct? What am I missing here?

推荐答案

echo 是bash内置的:

$ type echo
echo is a shell builtin

这意味着在运行 echo 时不会创建新进程.所有的工作都由 bash 进程完成，效率更高.

That means that a new process is not created when echo is run. All the work is done by the bash process instead, which is way more efficient.

您可以显式运行非内置的 echo :

You can run the non-builtin echo explicitly:

command echo "What is going on"

而是分叉并执行/bin/echo ，并使其显示在 ps 中.

This forks and execs /bin/echo instead, letting it show up in ps.

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