Bash Negate If

In bash scripting, the "if" statement is used to evaluate a condition and perform certain actions based on whether the condition is true or false. Sometimes, you may need to negate the condition, i.e., perform actions when the condition is false. This guide will explain how to negate an "if" statement in Bash.

Syntax of "if" statement

The syntax of the "if" statement in Bash is as follows:

if [ condition ]
then
    # code to be executed if condition is true
else
    # code to be executed if condition is false
fi

Negating the "if" condition

To negate the "if" condition, the logical operator ! (NOT) is used. It reverses the logical state of the condition. Here's an example:

if ! [ condition ]
then
    # code to be executed if condition is false
fi

Alternatively, you can also use the [[ keyword instead of [ for a more flexible and safer test command.

Example

Let's say we have a variable num containing a number, and we want to check if it is not equal to 10. We can use the negation operator as shown below:

num=5

if ! [ $num -eq 10 ]
then
    echo "The number is not equal to 10."
fi

In the above example, the code inside the "if" block will be executed because the condition ! [ $num -eq 10 ] evaluates to true. The string "The number is not equal to 10." will be printed.

Conclusion

In this guide, you learned how to negate an "if" condition in Bash using the ! (NOT) operator. Remember to use appropriate tests like -eq, -ne, etc., based on your condition. Negating conditions can be useful when you want to perform certain actions when the opposite condition is met.

Note: This introduction is written in markdown format.