Shell base-bash variable-user-defined variable

Variable setting rules:

Variable names can consist of letters, underscores, and numbers, but cannot start with a number.

The default type of a variable in bash is a string type, and if a numeric operation is required, specify the variable type as numeric. The variable is linked with an equal sign and cannot have spaces on either side. If a space is required, enclose it in single or double quotation marks.

The "\" in the bash variable is the escape character.

The value of the variable can be superimposed, but the variable needs to include the "$ variable name" or the ${variable name} in double quotation marks.

　　　　

If you assign the result of the command as a variable value, you need to use the inverse quotation mark ' or $ () to include the command

　　

Shell base-bash variable-user-defined variable