我需要命令 'env' 来设置临时环境变量吗？

Question

这两行命令有什么区别？

shy@nova:~/dev$ env TEST_VAR=demo mono test.exe
demo
shy@nova:~/dev$ TEST_VAR=demo mono test.exe
demo
shy@nova:~/dev$

test.exe 简单地写出 Environment.GetEnvironmentVariable("TEST_VAR") 的结果；到控制台。如您所见，无论有无 'env'，它都适用于两种情况。

这有什么解释吗？ 'env' 能否始终被省略，或者将其遗漏是一种不良行为？

Answer 1

来自Wikipedia's env lemma：

env is a shell command for Unix and Unix-like operating systems. It is used to either print a list of environment variables or run another utility in an altered environment without having to modify the currently existing environment.

[...]

To launch the X application xcalc and have it appear on a different display:

env DISPLAY=foo.bar:1.0 xcalc

Note that this use of env is often unnecessary since most shells support setting environment variables in front of a command:

DISPLAY=foo.bar:1.0 xcalc

所以，不，如果你的 shell 是“最 shell”之一。

Answer 2

试试这个来源 https://www.mkssoftware.com/docs/man1/env.1.asp.

据我所知，大多数 shell 不需要 env，除非您想显式设置或更改环境变量。