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This article focuses on "how to understand Shell script to define variables and reassign values", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "how to understand Shell scripts to define variables and reassign values".

Shell supports custom variables.

Define variable

When you define a variable, the variable name is not marked with a dollar sign ($), such as:

The code is as follows:

VariableName= "value"

Note that there can be no spaces between the variable name and the equal sign, which may be different from all the programming languages you are familiar with. At the same time, the naming of variable names must follow the following rules:

The first character must be a letter (a murz.Amurz).

There can be no spaces in the middle, you can use an underscore (_).

You cannot use punctuation.

You cannot use keywords in bash (you can view reserved keywords with the help command).

The curly braces outside the variable name are optional, whether to add them or not, and the curly braces are added to help the interpreter identify the boundaries of the variable, as in the following case:

The code is as follows:

For skill in Ada Coffe Action Java

Do

Echo "I am good at ${skill} Script"

Done

If you don't add curly braces to the skill variable and write it as echo "I am good at $skillScript", the interpreter will treat $skillScript as a variable (its value is empty), and the code execution result will not be what we expected.

It is recommended to add curly braces to all variables, which is a good programming habit.

Redefine variables

Defined variables can be redefined, such as:

The code is as follows:

Your_name= "tom"

Echo $your_name

Your_name= "alibaba"

Echo $your_name

It's legal to write this way, but note that you can't write $your_name= "alibaba" on the second assignment, but only add the dollar sign ($) when using variables.

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