如何从变量运行脚本命令? [英] How to run script commands from variables?

问题描述

我尝试使用管道运行命令.

I tried to run commands using pipes.

基本:

single="ls -l"
$single

可以正常工作

管道:

multi="ls -l | grep e"
$multi
ls: |: No such file or directory
ls: grep: No such file or directory
ls: e: No such file or directory

...不足为奇

bash < $multi

$multi: ambiguous redirect

下次尝试

bash $multi
/bin/ls: /bin/ls: cannot execute binary file

仅

echo $multi > tmp.sh
bash tmp.sh

工作.

是否可以在不创建执行脚本的情况下执行更复杂的命令?

Is there a way to execute more complex commands without creating a script for execution?

推荐答案

您正在演示Shell与内核之间的区别.

You're demonstrating the difference between the shell and the kernel.

"ls -l"可通过系统execve()调用执行.您可以man execve获取详细信息，但这可能对您来说太多了.

"ls -l" is executable by the system execve() call. You can man execve for details, but that's probably too much detail for you.

"ls -l | grep e"需要shell解释才能设置管道.在不使用外壳的情况下，"|"字符只是作为ls的参数传递到execve()中.这就是为什么您看到没有这样的文件或目录"错误的原因.

"ls -l | grep e" needs shell interpretation to set up the pipe. Without using a shell, the '|' character is just passed into execve() as an argument to ls. This is why you see the "No such file or directory" errors.

解决方案:

cmd="ls -l | grep e"
bash -c "$cmd"

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