What Are the Operators Used in Shell Scripting?


Scott Campbell

Shell scripting is a powerful tool for automating tasks in the command line interface of a Unix-like operating system. To create effective shell scripts, it is important to understand the various operators that can be used to manipulate and compare data. These operators allow you to perform actions such as arithmetic calculations, string manipulations, logical evaluations, and more.

Arithmetic Operators

Arithmetic operators are used to perform calculations on numerical values. The following table lists the commonly used arithmetic operators:

  • Addition (+): Adds two numbers together.
  • Subtraction (-): Subtracts one number from another.
  • Multiplication (*): Multiplies two numbers together.
  • Division (/): Divides one number by another.
  • Modulo (%): Returns the remainder of division between two numbers.
  • Note: Arithmetic operations can also be performed using the expr command or double parentheses (( )).

String Operators

In shell scripting, you can also manipulate strings using different operators. The following table shows the commonly used string operators:

  • Concatenation (+= or .): Combines two strings together.
  • Length (#): Returns the length of a string.
  • Note: String manipulations can be done using commands like sed, awk, or by manipulating variables directly.

Comparison Operators

To evaluate conditions and make decisions in shell scripts, comparison operators are used. These operators compare values and return a Boolean result (true or false). The following table lists the commonly used comparison operators:

  • Equal (==): Checks if two values are equal.
  • Not equal (!=): Checks if two values are not equal.
  • Greater than (>), Greater than or equal to (>=): Checks if one value is greater than another.
  • Less than (<), Less than or equal to (<=): Checks if one value is less than another.

Logical Operators

In shell scripting, logical operators allow you to combine multiple conditions and perform logical evaluations. The following table shows the commonly used logical operators:

  • AND (&&): Returns true if both conditions are true.
  • OR (||): Returns true if either condition is true.
  • NOT (!): Reverses the result of a condition.

Assignment Operators

The assignment operator (=) is used to assign a value to a variable in shell scripting. Additionally, there are compound assignment operators that combine arithmetic or string operations with assignment. Some examples include:

  • x += y: Equivalent to x = x + y
  • x -= y: Equivalent to x = x - y
  • x *= y: Equivalent to x = x * y

These are just a few examples of the operators commonly used in shell scripting. By understanding and utilizing these operators effectively, you can create powerful and efficient shell scripts to automate various tasks in your Unix-like operating system.

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