Conditionals

Conditionals are used to make decisions in the script, and the if, elif (else if), and else statements are used to accomplish this. Here are some examples:

1. Condition tests

if [ "$variable" -lt 10 ]
then
    echo "Variable is less than 10."
elif [ "$variable" -eq 10 ]
then
    echo "Variable is equal to 10."
else
    echo "Variable is greater than 10."
fi

In this script, -lt stands for “less than”, -eq for “equal to”. These are condition tests. If the condition after if is true, the commands between then and elif (or else if there’s no elif) get executed. If the condition is false, we move to the next condition (elif or else).

2. String comparisons:

if [[ "$str1" == "$str2" ]]; then
    echo "Strings are equal."
else
    echo "Strings are not equal."
fi

3. Checking if a file exists:

if [[ -e filename ]]; then
    echo "File exists."
fi

4. Using logical operators (&& for “and”, || for “or”):

if [[ "$str1" == "value1" && "$str2" == "value2" ]]; then
    echo "Both conditions are true."
fi

5. Case statements

Bash supports case statements, which can simplify complex conditional logic. Here’s an example:

case "$variable" in
pattern1)
    echo "Pattern 1"
    ;;
pattern2)
    echo "Pattern 2"
    ;;
*)
    echo "Default case"
    ;;
esac

The * serves as the default case if no other patterns match. Each case ends with ;;.