a variable
variable name = variable value
E.g:
x=5
name="jie cao"
Notice:
1. Variables cannot start with a number
2. There are spaces at both ends of the equal sign
3. If the variable has spaces, use double quotes
two-variable call
echo $variablename
E.g:
echo $x
echo $name
three-variable superposition
x=123
x=“$x”456
x=${x}789
Four variable view
set
Options:
-u: If this option is set, an error will be reported when calling an undeclared variable. (No error is reported by default)
Five variable deletion
unset variable name