When writing Zsh scripts on Linux, conditionals play a crucial role in controlling the flow of your script based on certain conditions. In this blog post, we will explore the different types of conditionals available in Zsh and how to use them effectively.

If Statements

The most basic form of a conditional statement in Zsh is the if statement. This statement allows you to execute a block of code only if a particular condition is true. Here’s the syntax for an if statement in Zsh:

if [[ condition ]]; then
    # Code to be executed if the condition is true
else
    # Code to be executed if the condition is false
fi

You can replace condition with any valid expression that evaluates to either true or false. Some examples of conditions in Zsh include:

• String comparison: [[ $var == "text" ]]
• Numeric comparison: [[ $num -eq 10 ]]
• File existence: [[ -a $file ]]
• Variable is set: [[ -n $var ]]

Remember, when using variables in conditions, it’s recommended to enclose them in double quotes to handle cases where the variable contains spaces or special characters.

Case Statements

A case statement in Zsh allows you to perform different actions based on the value of a variable. It’s similar to the switch statement in other programming languages. Here’s the syntax for a case statement in Zsh:

case $var in
    pattern1)
        # Code to be executed if var matches pattern1
        ;;
    pattern2)
        # Code to be executed if var matches pattern2
        ;;
    pattern3)
        # Code to be executed if var matches pattern3
        ;;
    *)
        # Code to be executed if no pattern matches
        ;;
esac

Each pattern can be a string or a wildcard expression (e.g., * for any characters). You can also specify multiple patterns using | as a separator.

Logical Operators

Zsh provides several logical operators to combine conditions and create complex expressions. These operators include:

• AND (&&): Executes the following command only if the previous command succeeds. Example: [[ $var -gt 10 && $var -lt 20 ]]
• OR (||): Executes the following command only if the previous command fails. Example: [[ $var == "text" || $var == "word" ]]
• NOT (!): Negates the result of a condition. Example: [[ ! -d $dir ]]

By combining these operators with conditionals, you can create powerful and flexible scripts in Zsh.

Conclusion

Understanding and effectively using Zsh script conditionals is essential when writing scripts on Linux. Whether it’s controlling the flow of your script with if statements or handling different cases with case statements, conditionals allow you to make your scripts more dynamic and responsive. Remember to practice and experiment with different types of conditions and logical operators to become comfortable with using them in your scripts.