variables in shell script is not calculated correctly

Question

What is the mistake in my below shell script:

#!/bin/bash

total=0

for i in 1 2 3 4
do
    echo -n "Enter Passenger Name: "
    read pname
    
    echo -n "Enter Car Number: "
    read ncar

    echo -n "Enter Amount: "
    read amount

    echo -n "Enter Distance Travelled: "
    read dtravelled

    total=$((total + dtravelled))

    average=$(echo "$total 4" | awk '{print $1/$2}')

    if test $dtravelled -gt 10000 -a $dtravelled -le 7000
    then
        bpassenger=$((business_pass + 1))
    elif test $dtravelled -gt 7000 -a $dtravelled -le 5000
    then
        lpassenger=$((leisure_pass + 1))
    else
        opassenger=$((other_pass + 1))
    fi

    if test $i -eq 1
    then
        lname=$pname
        low=$dtravelled
    fi

    if test $dtravelled -lt $low
    then
        lname=$pname
        low=$dtravelled
    fi
    
    echo
done

echo "Total of distance travelled by the passengers: $total"
echo "Average distance travelled by the passengers: $average"
echo "Number of business passengers: $bpassenger"
echo "Number of leisure passengers: $lpassenger"
echo "Number of other passengers: $opassenger"
echo "lowest distance travelled is $low by $lname."

***the below block is not calculated *** I always get empty output on this calculation

if test $dtravelled -gt 10000 -a $dtravelled -le 7000
        then
            bpassenger=$((business_pass + 1))
        elif test $dtravelled -gt 7000 -a $dtravelled -le 5000
        then
            lpassenger=$((leisure_pass + 1))
        else
            opassenger=$((other_pass + 1))
        fi

output:

bash mySript.sh

Enter Passenger Name: ahmad
Enter Car Number: 9889
Enter Amount: 20
Enter Distance Travelled: 1100

Enter Passenger Name: sara
Enter Car Number: 5214
Enter Amount: 300
Enter Distance Travelled: 1120

Enter Passenger Name: mohammad
Enter Car Number: 9713
Enter Amount: 6
Enter Distance Travelled: 500

Enter Passenger Name: nora
Enter Car Number: 98765
Enter Amount: 41
Enter Distance Travelled: 7500

Total of distance travelled by the passengers: 10220
Average distance travelled by the passengers: 2555
***Number of business passengers:*** 
***Number of leisure passengers:*** 
Number of other passengers: 1
lowest distance travelled is 500 by mohammad.

This statement: if test $dtravelled -gt 10000 -a $dtravelled -le 7000 says "if the dtravelled variable is both greater than 10,000 and less than 7,000"... i.e. it will always evaluate to false, as there's no value that fits both, contrary conditions. — JohnLBevan
– JohnLBevan, Commented Dec 7, 2022 at 8:17

Socowi · Accepted Answer · 2022-12-08 09:44:39Z

2

When writing test $dtravelled -gt 10000 -a $dtravelled -le 7000 in normal mathematical notation, you see that it can never be true:

dtravelled > 10000 and dtravelled < 7000
⇔ 10000 < dtravelled < 7000
⇒ 10000 < 7000
⇒ False

Same for the other test with 7000 and 5000.

Adapt your logic. If you run into problems again, add set -x to the beginning of your script or execute it with bash -x scriptFile.sh. This will print the executed statements and variable contents, which will make debugging easier.

edited Dec 8, 2022 at 9:44

answered Dec 7, 2022 at 8:16

Socowi

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Comments

Dominique · Accepted Answer · 2022-12-08 10:08:46Z

0

I believe you can find everything in this line of code:

total=$((total + dtravelled))

... which should become:

total=$(($total + $dtravelled))

When you assign a variable, then you just put the name of the variable at the left side of the equal-sign:

var=...

When you use the value of a variable, which you do a the right side of the equal-sign, you must add a dollarsign:

...=...$var...

answered Dec 8, 2022 at 10:08

Dominique

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