Logical OR Operator in Bash Script

1. Logical OR Operator (||) in Bash
2. Logical OR Operator (||) With Non-Boolean Values
3. Use Logical OR Operator (||) in Bash Scripting

We will explain the logical OR operator (||) and how it works throughout this article. We will also give examples of how it can be used in Bash scripting.

Logical OR Operator (||) in Bash

The logical OR operator || processes multiple values. It is usually used with boolean values and returns a boolean value. It returns true if at least one of the operands is true. Returns false if all values are false.

Let’s give a few examples.

True  || False --> True
False || True  --> True
True  || True  --> True
False || False --> False

Logical OR Operator (||) With Non-Boolean Values

The return value will not be a boolean if the logical OR operator (||) is used with non-boolean values like strings and numbers. Consider the example below.

param1 || param2 || param3

If the boolean value of param1 is true, it returns the value of this operand, and the other operands are ignored. Otherwise, param2 is checked.

If its boolean value is true, the result is the value of param2, and the rest of the operands are ignored. This process continues until the last operand.

If the boolean value of the last operand is also not true, the result is the last operand’s value.

The boolean value of the following expressions is false. The rest is true.

• 0
• NaN
• null
• undefined
• "", '' (Empty string)

Let’s give examples for non-boolean values.

1   || 0   --> 1
""  || 1   --> 1
""  || 0   --> 0
1   || "x" --> 1
"x" || 1   --> "x"

Use Logical OR Operator (||) in Bash Scripting

The logical OR operator (||) is the same in Bash scripting. Now, we will examine the example with Bash scripting syntax.

if [ 1 -eq 2 ] || [ 1 -eq 1 ]; then
        echo "The result of the operation is true"
else
        echo "The result of the operation is false"
fi

In the above if block, the operands are given to the logical OR operator (||). The result is false in the first comparison because 1 and 2 are not equal.

Since the two values are the same in the second comparison, they are equal, resulting in true. So, our process becomes false || true. This operation returns true, and the first echo command runs as we explained above.

We can also use the -o flag for this operation.

if [ 1 -eq 2 -o 3 -eq 4 ]; then
        echo "The result of the operation is true"
else
        echo "The result of the operation is false"
fi

The logic of this code is the same as the first one. But this time, the result of the operation will be false as both comparisons are false. So, the echo command inside the else block runs.