Bash Function: Unary Operator Expected error

Question

I am learning bash scripting and currently having trouble with an if statement inside a function. The following code returns two errors; both of which reference the if and elif conditions and say [: 12000: unary operator expected.

function calculateBonus {
    # If the sales figure is greater than 1 million, bonus is £1500
    if [ $1 >= 1000000 ]
    then
        bonus=1500
    # If greater than 100000, bonus is £750
    elif [ $1 >= 100000 ]
    then
        bonus=750
    else
        bonus=0
    fi

    # Return the bonus figure
    return $bonus
}

read sales
bonus=$(calculateBonus $sales)

I have tried using double square brackets, but I'm given a syntax error for some reason. Could someone explain the reason for the error above and for the syntax error when I use [[ some_condition ]] instead of [ some_condition ].

IIRC the operators for greater equal aren't >= but -ge. Look into man test (test should be the same as [) — Daniel Jour
– Daniel Jour, Commented Feb 14, 2016 at 19:06

e0k · Accepted Answer · 2016-02-14 19:21:00Z

2

Try this:

function calculateBonus() {
    if (( $1 >= 1000000 )); then
        bonus=1500
    elif (( $1 >= 100000 )); then
        bonus=750
    else
        bonus=0
    fi
}

read sales
calculateBonus "$sales"
echo "Bonus is $bonus"

The (()) is arithmetic evaluation. The function sets the variable bonus which can be used after the function is called. The return in a function does not do what you might think it does (it's an exit code). See also this article about returning values from a function.

This article has a nice discussion on the various test constructs, with examples.

answered Feb 14, 2016 at 19:21

e0k

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1 Comment

ryansin Over a year ago

Thanks e0k, very comprehensive and answered another question I had

riteshtch · Accepted Answer · 2016-02-14 19:22:05Z

1

function calculateBonus {
# If the sales figure is greater than 1 million, bonus is £1500
if [ $1 -ge 1000000 ]
then
    bonus=1500
# If greater than 100000, bonus is £750
elif [ $1 -ge 100000 ]
then
    bonus=750
else
    bonus=0
fi

}

read sales
calculateBonus $sales
echo $bonus

-ge=>greater than or equal to

see man test which is same as [, help [ directs you to man test

<, > are used for string comparison in bash(dictionary/lexicographical order)

Note: bash also has an advanced if condition operator [[ that has all features of test or [ plus more, see help [[

edited Feb 14, 2016 at 19:22

answered Feb 14, 2016 at 19:17

riteshtch

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2 Comments

ryansin Over a year ago

Ah I see, thanks a lot that's sorted it. Separately from this; when I echo $bonus, it doesn't echo anything. Why is the return value from calculateBonus not assigned to $bonus?

ryansin Over a year ago

In this instance yeah I can. But if I need to return a value to a variable instead of just echoing it, why would the above not work?

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