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How to use Shell variable in Linux, for this problem, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and easy way.

I. the use of local variables

Local variables, like local variables, only work in this SHELL. It does not affect variables in other SHELL.

one. Display the value of the variable

You can use the echo command. It is important to note that when using a variable, you must precede the variable name with a $symbol.

two. Clear variabl

Use the unset command to clear the command.

three. Show all local Linux Shell variables

Some environment variables are predefined in SHELL. To display these commands, you can use the set command.

In addition, local variables that have been defined by the user themselves are also displayed.

four. Test whether the variable has been assigned

${variable:-value}

If the variable is already assigned, the variable value is used. If the variable is empty, value is used. It is important to note that value is not assigned to variable.

${variable:=value}

The difference in this expression is that if variable is empty, value is assigned to variable.

If you need to verify that the variable is empty, and if so, display a system error message, use the following expression:

${variable:?}

If you need to display the information you define, it is as follows:

${variable:? "customed message"}

five. Set read-only variables

Using readonly, you can define variables as read-only.

Readonly variable

Execute readonly alone to display all read-only variables.

Second, environmental variables

Environment variables are used for all user processes. In Linux, the login process is called the parent process, and the user programs executed in shell are called child processes.

Environment variables can be set on the command line, but these values are lost when the user logs out. So * * is defined in .profile in the $HOME/ directory.

Traditionally, environment variables are capitalized. Environment variables must be exported with the export command before they can be applied to the user process. The setting method is the same as the local variable setting method.

one. Show environment variables

Use the env command to view all environment variables

two. Sneak into the SHELL variable

EXINIT saves initialization options using the vi editor. For example, to display a line number, it would be as follows:

EXINIT='set nu';export EXINIT

HOME: the home directory used to record users

IFS: used as the default domain delimiter specified by shell.

PATH: saves the order of directories for command or script lookups. It can be set in .profile.

three. Export variables to child processes

Use the export command in the parent script to export the variable so that the script knows the value of the variable. 54com.cn

Third, position variable parameters

You can use this location variable to get parameters when passing parameters to the script.

They are:

$0: script name. This variable contains the address, and you can use basename $0 to get the script name.

$1 virtual parameters *

$2, 3, 4, 4, 5... An analogy.

IV. Specific variable parameters

Some control information about script running

$# number of parameters passed to the script

$* display all parameters passed to the script in a single string

$the ID number under which the script is run

$! The ID number of a process running in the background

$@ is the same as $#, but use it in quotation marks and return each parameter in quotation marks.

$- displays the current options used by shell.

$? Displays the launch status of the * command. 0 means there are no errors.

This is the answer to the question about how to use Shell variables in Linux. I hope the above content can be of some help to you. If you still have a lot of doubts to solve, you can follow the industry information channel to learn more about it.

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