Use of expr in the shell

The expr command takes an arithmetic expression as a parameter, usually in the following form:

expr [number] [operator] [number]

Because the shell stores variables as characters, the user must ensure that the operand that participates in the arithmetic operation must be numeric. The following are valid arithmetic operators:

+ two integers added

-first number minus second number

* Multiply two integers

/First integer divided by second integer

% two integers divide, take remainder

For example:

[Root@mail root]# expr 2 + 1

Results showed: 3

[Root@mail root]# expr 5-3

Results showed: 2

If one of the arguments to expr is a variable, replace the variable name with the variable value before the expression evaluates.

[Root@mail root]# int=3

[Root@mail root]# expr $int + 4

Results showed: 7

Users can not simply use "*" to do multiplication, if input:

[Root@mail root]# expr 4*5

The system will get an error, because the shell will see "*" to replace the file name first. The correct form is:

[[email protected] root]# Expr 4 \* 5

Results showed: 20

Multiple arithmetic expressions can be grouped together, for example:

[[email protected] root]# Expr 5 + 7/3

Results showed: 7

The order of operations is preceded by multiplication, and to change the order of operations, the "'" number must be used, such as:

[[email protected] root]# int= ' expr 5 + 7 '

[[email protected] root]# expr $int/3

Results showed: 4

Or:

[[email protected] root]# expr ' expr 5+7 '/3

Results showed: 4

Use of expr in the shell