conditional-statements.md

Title	Description	Subjects	Tags	CatalogContent
Conditional Statements	Allow a script to make decisions based on conditions.	Bash/Shell Computer Science	Bash/Shell Command Line Script Conditionals	learn-the-command-line paths/computer-science

Conditional statements in Bash allow a script to make decisions based on conditions. These statements help in controlling the flow of execution by performing different actions based on whether a condition evaluates to true or false. Bash supports several types of conditional checks, including comparisons between numbers, strings, and file conditions.

Syntax

Bash conditional statements are typically written using if, elif, else, and fi keywords. The basic syntax is:

if [ condition ]; then
  # Code to execute if condition is true
elif [ another_condition ]; then
  # Code to execute if another_condition is true
else
  # Code to execute if no conditions are met
fi

Basic Operators

The different operators that Bash provides can be classified into several categories based on the data type of the operands.

Numeric Operators:

Operator	Description
-eq	Equal to
-ne	Not equal to
-lt	Less than
-le	Less than or equal to
-gt	Greater than
-ge	Greater than or equal to

String Operators:

Operator	Description
=	Equal to
!=	Not equal to
-z	String is empty
-n	String is not empty

File Test Operators:

Operator	Description
-e	File exists
-f	File is a regular file
-d	File is a directory
-r	File is readable
-w	File is writable
-x	File is executable

Example

Here is an example that takes a number from the user and then uses conditional statements in Bash to check if the number is greater than, less than, or equal to 0:

#!/bin/bash

read -p "Enter a number: " num

if [ "$num" -gt 0 ]; then
  echo "The number is positive."
elif [ "$num" -lt 0 ]; then
  echo "The number is negative."
else
  echo "The number is zero."
fi

The above code produces the following output if the user inserts the number 5 when prompted:

Enter a number: 5
The number is positive.