bash 在bash one-liner中为多个命令设置环境变量
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Setting environment variables for multiple commands in bash one-liner
提问by Pavel K.
Let's say I have following command
假设我有以下命令
$> MYENVVAR=myfolder echo $MYENVVAR && MYENVVAR=myfolder ls $MYENVVAR
$> MYENVVAR=myfolder echo $MYENVVAR && MYENVVAR=myfolder ls $MYENVVAR
I mean that MYENVVAR=myfolder repeats
我的意思是 MYENVVAR=myfolder 重复
Is it possible to set it once for both "&&" separated commands while keeping the command on one line?
是否可以在将命令保留在一行的同时为两个“&&”分隔的命令设置一次？
回答by Jonathan Leffler
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（即使示例代码并不真正需要环境变量；一些 shell 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.
括号创建一个子壳；在子 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，变量设置一次，然后使用两次，两个命令中的每一个都使用一次。
回答by Leonid Volnitsky
Parentheses spawn new proces, where you can set its own variables:
括号产生新的过程，您可以在其中设置自己的变量：
( MYENVVAR=myfolder; echo 1: $MYENVVAR; ); echo 2: $MYENVVAR;
1: myfolder
2:
