linux中设置环境变量Wondering how to set environment variables in Linux? This is exactly what we’ll be doing in this tutorial. Operating systems make use of environment variables to define system ...
linux中设置环境变量
Wondering how to set environment variables in Linux? This is exactly what we’ll be doing in this tutorial. Operating systems make use of environment variables to define system properties for the runtime environment.
Through this tutorial, we will help you understand how environment variables work. Further, we will see how to set environment variables in Linux or reset existing environment variables as per our needs.
When we start a session on our server through the shell, it has to create an environment for us. This is a mandatory step for us to interact with the server through the shell.
All variable names are case-sensitive. We provide all environment variables with an uppercase name by convention. 所有变量名称均区分大小写。 根据约定，我们为所有环境变量提供一个大写名称。
When assigning a value to our variable, we make sure there is no space around the assignment operator (=). 在为变量赋值时，请确保赋值运算符（=）周围没有空格。
If we need to assign multiple values to a single environment variable, we make use of a colon (:) to separate the different values. 如果需要为单个环境变量分配多个值，则可以使用冒号（:)分隔不同的值。
列出Linux中的现有环境变量 (List existing Environment Variables in Linux)
If we want to see the environment variables for our current session, we use the following command.
如果要查看当前会话的环境变量，请使用以下命令。
printenv
Print Environment Variables In Linux Systems
Linux系统中的打印环境变量
As seen in the screenshot above, this command will print all the variables for the current shell session. If we want a list of shell variables with environment variables, we use this command.
This will return a similar output displaying the shell variables for the current shell session.
这将返回一个类似的输出，显示当前shell会话的shell变量。
Below are some examples of environment variables with their importance.
以下是一些环境变量及其重要性的示例。
Type of Variable
Significance
SHELL
The shell which interprets all the commands entered by the user. Usually, this will be set to bash by default. But users can change it as per their to suit their needs.
USER
The username of the user currently logged on to the system.
LANG
The language and localization settings for the system currently in place, which includes character encoding.
TERM
The type of terminal which needs to be emulated when the shell is running. While this isn’t something you would need to usually worry about, there can be instances when your operating needs might require emulating a specific hardware terminal.
HOME
The home directory for the user currently logged on to the system.
PATH
The list of directories in which our system will check when a command is entered by the user. This search of directories is done to find the executable files associated with the command.
PWD
The current directory which the user is working with.
Now, if you run the printenv command with the variable name as shown below, you will not get any output since the variable is currently a shell variable
3.替代方案–结合两个步骤 (3. Alternative – Combining the two steps)
There is a more commonly used method when you want to set environment variables in Linux. We can use the below line to declare and export the variable at the same time.
要在Linux中设置环境变量时，有一种更常用的方法。 我们可以使用下面的行来同时声明和导出变量。
export NEWTESTVAR="This is a new test variable"
printenv NEWTESTVAR
One Line Set Environment Variables In Linux 1
Linux 1中的一个行集环境变量
Now when we use the printenv command for our new variable, we will see that it displays the environment variable right away.
现在，当我们对新变量使用printenv命令时，我们将看到它立即显示环境变量。
如何在Linux中删除环境变量 (How to delete environment variables in Linux)
Now that we know how to set environment variables in Linux, we need to learn how to remove them. Once we have no use for our created environment variables, it is advised to delete them.
This ensures that the environment variable isn’t called unintentionally.
这样可以确保不会意外调用环境变量。
1.使用导出命令 (1. Using the export Command)
export -n TESTVAR
printenv TESTVAR
Now, if we try using the printenv command to get the value of TESTVAR, we will get no output.
现在，如果尝试使用printenv命令获取TESTVAR的值，则不会获得任何输出。
This confirms that TESTVAR is no longer an environment variable.
这确认TESTVAR不再是环境变量。
2.使用unset命令 (2. Using the unset Command)
Alternatively, we can use the unset command. Using it will remove the variable completely so that it is neither an environment variable nor a shell variable.
Notice that nothing is returned even when we use the echo command. Thus, we know that the variable is unset.
请注意，即使使用echo命令，也不会返回任何内容。 因此，我们知道该变量未设置。
结论 (Conclusion)
With environment variables having so much control over how our shell session functions, it is important for any shell user to understand how to set environment variables in Linux.
su root vim /etc/sudoers.d/sfapp sfapp ALL=(ALL) ALLsfapp ALL=(ALL) NOPASSWD: ALL Defaults !env_reset :wq! 转载于:https://www.cnblogs.com/xinfang520/p/10298248.html
