前缀变量分配不适用于echo [英] Prefixing variable assignment doesn't work with echo

问题描述

据我所知，如果为bash命令添加变量分配前缀，则该变量将立即生效.而且只会在该命令中生效.

As far as I know, if you prefix a bash command with variable assignment the variable will take effect immediately. And it will only have effect within that command.

我在bash中尝试了此命令:

I tried this command in bash:

V=1 echo $V

但是终端中没有打印出1，这不是我期望的.那么为什么它不起作用?

However 1 is not printed out in the terminal which is not what I expected. So why it doesn't work?

推荐答案

变量将在紧随其后的命令环境中传递，而不是在评估(扩展)命令时传递.任何变量扩展都将由Shell提前完成.

The variable will be passed in the environment of the command following it, not when the command is being evaluated (expanded). Any variable expansion will be done earlier by shell.

$ V=1 env | grep V=
V=1

要使其正常工作:

$ V=1; echo $V
1

这篇关于前缀变量分配不适用于echo的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！