csh 中“setenv”的范围与 bash 中的“export”
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Scope of "setenv" in csh Versus "export" in bash
提问by Dao Lam
From what I've read, setenvin csh and exportin bash are equivalent. However, I found some strange issues while working with the two.
从我读过的内容来看，setenv在 csh 和exportbash 中是等效的。但是，在与两者合作时，我发现了一些奇怪的问题。
When I open putty and start typing:
当我打开腻子并开始输入时：
setenv TEMP yes
echo $TEMP //this give me "yes"
then I go to bash and type
然后我去 bash 并输入
echo $TEMP //this give me "yes" as well
However, if I do it in the opposite order, it wouldn't give the same results. Specifically, when I go to bash first and type
但是，如果我以相反的顺序执行此操作，则不会给出相同的结果。具体来说，当我先去 bash 并输入
export TEMP=no
echo $TEMP //this give me "no"
then I go back to csh and type
然后我回到 csh 并输入
echo $TEMP // this give me "Undefined Variable"
Shouldn't it give me "no" as well? Am I missing something?
它不应该也给我“不”吗？我错过了什么吗？
Thank you!
谢谢！
回答by rici
Exporting a variable means that a copy of that variable is placed into the environment of any newly created child processes. It is a copy of the variable; if the child process modifies the variable, the parent does not see the modification. Moreover, if a child exports a variable, it does not become visible in the parent.
导出变量意味着将该变量的副本放入任何新创建的子进程的环境中。它是变量的副本；如果子进程修改了变量，则父进程看不到修改。此外，如果子项导出变量，它在父项中是不可见的。
Hence, your two cases are asymmetrical. When you start in csh, export a variable, and then start bash, bash sees the exported variable. When you then export a new variable in bash and exit from bash to go back to csh, all of the variables created in the bash session disappear.
因此，您的两个案例是不对称的。当你在csh中启动，导出一个变量，然后启动bash，bash看到的是导出的变量。当您随后在 bash 中导出一个新变量并从 bash 退出以返回到 csh 时，在 bash 会话中创建的所有变量都将消失。
If you were to export a variable in bash and then start up a child csh (by typing csh), you would almost certainly see the exported variable.
如果您要在 bash 中导出一个变量，然后启动一个子 csh（通过键入csh），您几乎肯定会看到导出的变量。
