在bash一行程序中为多个命令设置环境变量

Let's say I have following command

假设我有如下命令

$> MYENVVAR=myfolder echo $MYENVVAR && MYENVVAR=myfolder ls $MYENVVAR

$> MYENVVAR= MYENVVAR=myfolder echo $MYENVVAR && MYENVVAR=myfolder ls $MYENVVAR

I mean that MYENVVAR=myfolder repeats

MYENVVAR=重复文件夹

Is it possible to set it once for both "&&" separated commands while keeping the command on one line?

是否可以对“&&”两个分开的命令设置一次，同时将命令保持在一行?

3 个解决方案

#1

Assuming you actually need it as an environment variable (even though the example code does not really need an environment variable; some shell variables are not environment variables):

假设您实际上需要它作为环境变量(即使示例代码实际上并不需要环境变量;有些壳变量不是环境变量):

(export MYENVVAR=myfolder; echo $MYENVVAR && ls $MYENVVAR)

If you don't need it as an environment variable, then:

如果您不需要它作为环境变量，则:

(MYENVVAR=myfolder; echo $MYENVVAR && ls $MYENVVAR)

The parentheses create a sub-shell; environment variables (and plain variables) set in the sub-shell do not affect the parent shell. In both commands shown, the variable is set once and then used twice, once by each of the two commands.

圆括号创建子shell;子shell中设置的环境变量(和普通变量)不会影响父shell。在显示的两个命令中，变量被设置一次，然后被两个命令分别使用两次。

#2

Parentheses spawn new proces, where you can set its own variables:

圆括号产生了新的过程，在这里你可以设置自己的变量:

( MYENVVAR=myfolder; echo  1: $MYENVVAR; ); echo  2: $MYENVVAR;
1: myfolder
2:

#3

Did you consider using export like

你考虑过使用export like吗

export MYENVVAR=myfolder

then type your commands like echo $MYENVVAR (that would work even in sub-shells) etc

然后输入您的命令，如echo $MYENVVAR(即使在子shell中也可以)等

#1