UNIX Shell basic operator

Shell basic operator

Each shell supports a wide variety of operators. Our tutorial is based on the default Shell (Bourne), so all the important Bourne Shell operators are covered in our tutorial.

Here are the operators we'll discuss:

• Arithmetic operator.
• The relationship operator.
• Boolean operator.
• String operator.
• The file test operator.

The original Bourne Shell did not have any mechanism to perform simple arithmetic operations, it used an external program awk or the simplest program expr.

Let's illustrate with a simple example that the two numbers add up:

    #!/bin/sh

    val=`expr 2 + 2`
    echo "Total value : $val"

This results in the following:

    Total value : 4

Note the following:

• There must be a space between the operator and the expression, such as 2 plus 2 is incorrect, and should be written here as 2 plus 2.
• The complete expression should be enclosed between two single quotes ''.

Arithmetic operator

The arithmetic operators supported by Bourne Shell are listed below.

Suppose variable a is assigned 10 and variable b is assigned 20:

It is important to note here that all conditional expressions and operators must be separated by spaces, for example, $a $b is correct, and $a is not. $b. is incorrect.

All arithmetic calculations are performed for long integers.

The relationship operator

Bourne Shell supports the following relationship operators, which are specific to numeric data. They do not work on string values unless their values are numeric data.

For example, the following operator examines the relationship between 10 and 20 and the relationship between "10" and "20", but cannot be used to determine the relationship between "ten" and "twenty".

Suppose variable a is assigned 10 and variable b is assigned 20:

It is important to note here that all conditional expressions and operators must be separated by spaces, for example, the $a $b is correct, and the $a $b is not correct.

Boolean operator

Bourne Shell supports the following Boolean operators.

Suppose variable a is assigned 10 and variable b is assigned 20:

String operator:

Bourne Shell supports the following string operators.

Suppose variable a is assigned "abc" and variable b is assigned "efg":

Example description

File test operator:

The following operators are used to test the various properties associated with the Unix file.

Suppose a file variable file contains a file name "test" with a file size of 100 bytes with read, write, and execute permissions:

Example description