setenv (添加或更改環境變量的值)

瑞茲發表于 2020-11-30 09:03

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命令行 Unix&Linux命令 setenv

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在運行C shell類的Unix操作系統上，setenv內置命令會添加或更改環境變量的值。

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1 setenv 運行系統環境

2 setenv 語法

3 setenv 例子

setenv 運行系統環境

Unix&Linux

setenv 語法

setenv VAR [ VALUE ]

爭論

VAR	要設置的變量的名稱。
VALUE	變量的值，可以是單個單詞，也可以是帶引號的字符串。

描述

setenv是C shell（csh）的內置函數。它用于定義環境變量的值。

如果沒有給setenv參數，它將顯示所有環境變量及其值。如果僅指定VAR，則它將該名稱的環境變量設置為空（null）值。如果兩個VAR和VALUE是指定的，它集命名變量VAR的值VALUE。setenv類似于set命令，該命令還設置環境變量的值。但是，與set不同，setenv還將此環境變量“導出”到任何子shell。這樣，它等效于bash命令出口。

例如，如果您在c shell中，則使用setenv設置以下變量：

setenv MYVAR myvalue

然后，我們可以使用echo命令查看該變量的值：

echo"$MYVAR"

myvalue

我們的值“ myvalue ”被返回。現在讓我們將bash作為子shell運行：

bash

并查看它是否知道變量MYVAR的值：

echo"$MYVAR"

myvalue

如您所見，MYVAR的值傳遞給bash。

現在，讓我們看看set有何不同。讓我們退出bash子外殼，回到csh：

exit

...并使用set設置另一個環境變量MYVAR2：

set MYVAR2 = myvalue2

（如您所見，set的語法略有不同。它使用等號分配值。）現在，讓我們檢查MYVAR2的值：

echo"$MYVAR2"

myvalue2

現在讓我們回到bash：

bash

...并檢查MYVAR2的值：

echo"$MYVAR2"

這次，沒有報告任何值，因為該變量未“導出”到子shell。因此，當您使用csh時，如果您希望環境變量僅在當前外殼程序中保持局部狀態，請使用set。如果您還希望它們繼承到子shell，請使用setenv。

setenv VAR [VALUE]

Arguments

VAR	The name of the variable to be set.
VALUE	The value of the variable, as either a single word or a quoted string.

Description

setenv is a built-in function of the C shell (csh). It is used to define the value of environment variables.

If setenv is given no arguments, it displays all environment variables and their values. If only VAR is specified, it sets an environment variable of that name to an empty (null) value. If both VAR and VALUE are specified, it sets the variable named VAR to the value VALUE. setenv is similar to the set command, which also sets an environment variable's value. However, unlike set, setenv also "exports" this environment variable to any subshells. In this way, it is the equivalent of the bash command export.

For instance, if you are inside the c shell, and you use setenv to set the following variable:

setenv MYVAR myvalue

We can then use the echo command to view the value of that variable:

echo "$MYVAR"

myvalue

Our value, "myvalue", was returned. Now let's run bash as a subshell:

bash

and see if it knows the value of our variable MYVAR:

echo "$MYVAR"

myvalue

As you can see, the value of MYVAR was passed on to bash.

Now, let's see how set is different. Let's go back to csh by exiting the bash subshell:

exit

...and use set to set another environment variable, MYVAR2:

set MYVAR2=myvalue2

(The syntax of set, as you can see, is slightly different. It uses an equals sign to assign a value.) Now let's check the value of MYVAR2:

echo "$MYVAR2"

myvalue2

And now let's go back to bash:

bash

...and check the value of MYVAR2:

echo "$MYVAR2"

This time, no value is reported, because the variable was not "exported" to the subshell. So, when you are using csh, if you want environment variables to remain local to only the current shell, use set. If you want them to carry over to subshells as well, use setenv.

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setenv 例子

setenv PATH "/bin:/usr/bin:/usr/sbin:/usr/local/bin"

設置環境變量PATH。PATH是用冒號（“：”）分隔的路徑名列表，這些是調用命令時搜索可執行文件的默認路徑。將PATH設置為上述值后，shell將按順序在路徑/bin、/usr/bin、/usr/sbin和/usr/local/bin中查找您運行的任何后續命令的可執行文件。

setenv PATH "/bin:/usr/bin:/usr/sbin:/usr/local/bin"

Sets the environment variable PATH. PATH is a list of path names separated by colons (":"), which are the default paths to search for executable files when a command is called. After you set PATH to the above value, the shell will look in the paths /bin, /usr/bin, /usr/sbin, and /usr/local/bin, in that order, for the executable files of any subsequent commands that you run.

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