Shell Scripting Conditional statements

In shell scripting, conditional statements are used to perform different actions based on the outcome of a comparison or test. There are several types of conditional statements that can be used, including if, if-else, if-elif-else, and case.

1. if statement: The if statement is used to perform an action if a certain condition is true. For example:

if [ "$x" -gt "0" ]; then
    echo "x is greater than 0."
fi

2. if-else statement: The if-else statement is used to perform one action if a condition is true and another action if the condition is false. For example:

if [ "$x" -gt "0" ]; then
    echo "x is greater than 0."
else
    echo "x is not greater than 0."
fi

3. if-elif-else statement: The if-elif-else the statement is used to perform different actions based on multiple conditions. For example:

if [ "$x" -gt "0" ]; then
    echo "x is greater than 0."
elif [ "$x" -eq "0" ]; then
    echo "x is equal to 0."
else
    echo "x is less than 0."
fi

4. case statement: The case statement is used to perform different actions based on a single variable. For example:

case $x in
    1) echo "x is 1.";;
    2) echo "x is 2.";;
    *) echo "x is not 1 or 2.";;
esac

It’s important to note that the test conditions used in the if, if-else, if-elif-else and case statements are enclosed in square brackets ([]) and not paranthesis (()) as used in other programming languages. Also, it’s good practice to use double paranthesis ([[ ]]) instead of single paranthesis ([]) for more advanced tests, as it provides additional functionality.

It’s also good practice to use quotes around variables in the test conditions to prevent errors caused by spaces or special characters in the variable’s value.